The Diagnostic Process: Strategy-Based Diagnosis

chapter 1 THE DIAGNOSTIC PROCESS After studying this chapter, the reader should be able to: 1. List the steps of the diagnostic process. 2. Discuss the type of scan tools that are used to assess vehicle components. 3. Describe how to retrieve diagnostic information from a vehicle. 4. Explain the troubleshooting procedures to follow if a diagnostic trouble code has been set. 5. Describe diagnostic trouble code retrieval, diagnosis, and testing for OBD-II vehicles. 6. Explain the troubleshooting procedures to follow if no diagnostic trouble code has been set. 7. List the steps in most manufacturers' diagnostic routines. 8. Describe how to verify the repair and conduct a universal drive cycle. 9. Describe how to run OBD-II monitors on a light duty diesel vehicle. LEARNING OBJECTIVES 1 Data link connector (DLC) 7 Drive cycle 20 Flash code retrieval 11 No-code diagnosis 17 Paper test 5 Pending code 6 Smoke machine 5 Strategy-based diagnosis 2 Technical service bulletin (TSB) 7 Trip 16 KEY TERMS 2 chapter 1 STRATEGY-BASED DIAGNOSIS Successful diagnose depends on using the same process for all problems and customer concerns to arrive at the root cause of the problem. The process is called strategy-based diagnosis. Many different things can cause an engine performance problem or concern. The service technician has to narrow the possibilities to find the cause of the problem and correct it. A funnel is a way of visualizing a diagnostic procedure. ● SEE FIGURE 1–1. At the wide top are the symptoms of the prob-lem; the funnel narrows as possible causes are eliminated until the root cause is found and corrected at the bottom of the funnel. All problem diagnosis deals with symptoms that could be the result of many different causes. The wide range of pos-sible solutions must be narrowed to the most likely and these must eventually be further narrowed to the actual cause. The following section describes eight steps the service technician can take to narrow the possibilities to one cause. STEP 1 VERIFY THE PROBLEM (CONCERN) Before a minute is spent on diagnosis, be certain that a problem exists. THE EIGHT-STEP DIAGNOSTIC PROCEDURE If the problem cannot be verified, it cannot be solved or tested to verify that the repair was complete. ● SEE FIGURE 1–2. The driver of the vehicle knows much about the vehicle and how it is driven. Before diagnosis, always ask the following questions: ■ ■Is the malfunction indicator light (check engine) on? ■ ■What was the temperature outside? ■ ■Was the engine warm or cold? ■ ■Was the problem during starting, acceleration, cruise, or some other condition? ■ ■How far had the vehicle been driven? ■ ■Were any dash warning lights on? If so, which one(s)? ● SEE FIGURE 1–3. ■ ■Has there been any service or repair work performed on the vehicle lately? NOTE: This last question is very important. Many engine performance faults are often the result of something being knocked loose or a hose falling off during repair work. Knowing that the vehicle was just serviced before the problem began may be an indicator as to where to look for the solution to a problem. After the nature and scope of the problem are determined, the complaint should be verified before further diagnostic tests are performed. A sample form that customers could fill out with details of the problem is shown in ● FIGURE 1–4. CUSTOMER SATISFACTION CODES CLEARED REPAIR CONFIRMED REPAIRS COMPLETED DIAGNOSTIC STEPS TO LOCATE ROOT CAUSE OF PROBLEM CUSTOMER CONCERN FIGURE 1–1 A funnel is one way to visualize the diagnostic process. The purpose is to narrow the possible causes of a concern until the root cause is determined and corrected. CUSTOMER SATISFACTION FIGURE 1–2 Step #1 is to verify the customer concern or problem. If the problem cannot be verified, then the repair cannot be verified. THE DIAGNOSTIC PROCESS 3 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 1. Anit-Lock Brake System Warning 2. Gas Cap Loose 3. Low Coolant Level Detected 4. Low Fuel 5. Malfunction Indicator Lamp (MIL) 6. Reduced Power 7. Service Required 8. Theft Deterrent 9. Time for Maintenance Indicator 10. Transmission Warning 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 1. Battery/Alternator Warning 2. Catalytic Converter Warning 3. Electronic Throttle Control 4. Ignition Switch Warning 5. Low Coolant Level Warning 6. Oil Level Low 7. Oil Pressure Low 8. Temperature Warning 9. Theft Deterrent Fault 10. Transmission Fault - Do Not Shift 11. Transmission Fluid Temp Warning FIGURE 1–3 The amber dash warning symbols indicate that a fault has been detected. A red dash warning light indicates that a major fault has been detected requiring action by the driver as soon as possible. NOTE: Because drivers differ, it is sometimes the best policy to take the customer on the test-drive to verify the concern. STEP 2 PERFORM A THOROUGH VISUAL INSPECTION AND BASIC TESTS The visual inspection is the most important aspect of diagnosis! Most experts agree that between 10% and 30% of all engine performance problems can be found simply by performing a thorough visual inspection. The inspection should include the following: ■ ■Check for obvious problems (basics, basics, basics). Fuel leaks Vacuum hoses that are disconnected or split Corroded connectors Unusual noises, smoke, or smell Check the air cleaner and air duct (squirrels and other small animals can build nests or store dog food in them). ● SEE FIGURE 1–5. ■ ■Check everything that does and does not work. This step involves turning things on and observing that every-thing is working properly. ■ ■Look for evidence of previous repairs. Any time work is performed on a vehicle, there is always a risk that something will be disturbed, knocked off, or left disconnected. ■ ■Check oil level and condition. Another area for visual inspection is oil level and condition. Oil level. Oil should be to the proper level. Oil condition. Using a match or lighter, try to light the oil on the dipstick; if the oil flames up, gasoline is present 4 chapter 1 FIGURE 1–4 A form that the customer should fill out if there is a driveability concern to help the service technician more quickly find the root cause. THE DIAGNOSTIC PROCESS 5 FIGURE 1–5 This is what was found when removing an air filter from a vehicle that had a lack-of-power concern. Obviously the nuts were deposited by squirrels or some other animal, blocking a lot of the airflow into the engine. YELLOW PLASTIC CAP LEAK AT GASKET FIGURE 1–6 Using a bright light makes seeing where the smoke is coming from easier. In this case, smoke was added to the intake manifold with the inlet blocked with a yellow plastic cap and smoke was seen escaping past a gasket at the idle air control. in the engine oil. Drip some engine oil from the dip-stick onto the hot exhaust manifold. If the oil bubbles or boils, coolant (water) is present in the oil. Check for grittiness by rubbing the oil between your fingers. NOTE: Gasoline in the oil will cause the engine to run rich by drawing fuel through the positive crank-case ventilation (PCV) system. ■ ■Check coolant level and condition. Many mechanical engine problems are caused by overheating. The proper operation of the cooling system is critical to the life of any engine. NOTE: Check the coolant level in the radiator only if the radiator is cool. If the radiator is hot and the radiator cap is removed, the drop in pressure above the coolant will cause the coolant to boil immedi-ately, which can cause severe burns because the coolant expands explosively upward and outward from the radiator opening. ■ ■Use the paper test. even and steady exhaust flow at the tailpipe when running. For the paper test, hold a piece of paper (even a dollar bill works) or a 3-by-5-inch card within 1 inch (2.5 m) of the tailpipe with the engine running at idle. The paper should blow evenly away from the end of the tailpipe without “puffing” or being drawn inward toward the end of the tailpipe. If the paper is at times drawn toward the tailpipe, the valves in one or more cylinders could be burned. Other reasons why the paper might be drawn toward the tailpipe include the following: “Original Equipment” Is Not a Four-Letter Word To many service technicians, an original equipment (OE) part is considered to be only marginal and to get the really “good stuff” an aftermarket (renewal market) part has to be purchased. However, many problems can be traced to the use of an aftermarket part that has failed early in its service life. Technicians who work at dealerships usually begin their diagno-sis with an aftermarket part identified during a visual inspection. It has been their experience that simply replacing the aftermarket part with the factory OE part often solves the problem. OE parts are required to pass quality and du-rability standards and tests at a level not required of aftermarket parts. The technician should be aware that the presence of a new part does not necessarily mean that the part is good. TECH TIP Smoke Machine Testing Vacuum (air) leaks can cause a variety of driveabil-ity problems and are often difficult to locate. One good method is to use a machine that generates a stream of smoke. Connecting the outlet of the smoke machine to the hose that was removed from the vacuum brake booster allows smoke to enter the intake manifold. Any vacuum leaks will be spotted by observing smoke coming out of the leak. ● SEE FIGURE 1–6. TECH TIP 6 chapter 1 1. The engine could be misfiring because of a lean condi-tion that could occur normally when the engine is cold. 2. Pulsing of the paper toward the tailpipe could also be caused by a hole in the exhaust system. If exhaust escapes through a hole in the exhaust system, air could be drawn—in the intervals between the exhaust puffs—from the tailpipe to the hole in the exhaust, causing the paper to be drawn toward the tailpipe. ■ ■Ensure adequate fuel level. Make certain that the fuel tank is at least one-fourth to one-half full; if the fuel level is low, it is possible that any water or alcohol at the bot-tom of the fuel tank is more concentrated and can be drawn into the fuel system. ■ ■Check the battery voltage. The voltage of the battery should be at least 12.4 volts and the charging voltage (engine running) should be 13.5 to 15.0 volts at 2000 RPM. Low battery voltage can cause a variety of problems, including reduced fuel economy and incorrect (usually too high) idle speed. Higher-than-normal battery voltage can also cause powertrain control module (PCM) problems and could cause damage to electronic modules. ■ ■Check the spark using a spark tester. Remove one spark plug wire and attach the removed plug wire to the spark tester. Attach the grounding clip of the spark tester to a good clean engine ground, start or crank the engine, and observe the spark tester. ● SEE FIGURE 1–7. The spark at the spark tester should be steady and consistent. If an intermittent spark occurs, then this condition should be treated as a no-spark condition. If this test does not show satisfactory spark, carefully inspect and test all com-ponents of the primary and secondary ignition systems. NOTE: Do not use a standard spark plug to check for proper ignition system voltage. An electronic ig-nition spark tester is designed to force the spark to jump about 0.75 inch (19 mm). This amount of gap requires between 25,000 and 30,000 volts (25 and CUSTOMER SATISFACTION STEP# 3 VISUAL INSPECTION AND SIMPLE TESTS CUSTOMER CONCERN VERIFY THE PROBLEM FIGURE 1–8 Step 3 in the diagnostic process is to retrieve any stored diagnostic trouble codes. H E I SPARK TESTER FIGURE 1–7 A spark tester connected to a spark plug wire or coil output. A typical spark tester will only fire if at least 25,000 volts are available from the coil, making a spark tester a very useful tool. Do not use one that just lights when a spark is present, because they do not require more than about 2,000 volts to light. 30 kV) at atmospheric pressure, which is enough voltage to ensure that a spark can occur under compression inside an engine. ■ ■Check the fuel-pump pressure. Checking the fuel-pump pressure is relatively easy on many port-fuel-injected en-gines. Often the cause of intermittent engine performance is due to a weak electric fuel pump or clogged fuel filter. Checking fuel-pump pressure early in the diagnostic pro-cess eliminates low fuel pressure as a possibility. STEP 3 RETRIEVE THE DIAGNOSTIC TROUBLE CODES (DTCs) If a DTC is present in the computer memory, it may be signaled by illuminating a malfunction indicator lamp (MIL), commonly labeled “check engine” or “service engine soon.” ● SEE FIGURE 1–8. Any code(s) that is displayed on a scan tool when the MIL is not on is called a pending code. Because the MIL is not on, this indicates that the fault has not repeated to cause the PCM to turn on the MIL. Although this pending code is helpful to the technician to know that a fault has, in the past, been detected, further testing will be needed to find the root cause of the problem. Check and record the freeze-frame information. This indicates when the DTC was set, and this not only will help the technician determine what may have caused the code to set but also helps to verify the repair by operating the vehicle under the same or similar conditions. THE DIAGNOSTIC PROCESS 7 Perform Both a Pre-Scan and a Post-Scan Many experts advise shops to make a pre-scan of all the vehicle’s computer modules as well as a scan after the vehicle has been repaired to be a part of their stan-dard operation procedure (SOP). Not only is this good business practice, but it really helps communications with the customer about possible faults with the vehicle that may not be part of the original customer concern. • Pre-scan: This involves accessing all of the mod-ules in the vehicle and retrieving any or all of the stored diagnostic trouble codes (DTCs), including pending codes. Any stored DTCs are recorded on the work order, and if related to the customer concern, the customer may need to be notified to get their approval before proceeding with the repairs. • Post-scan: After the vehicle has been repaired and before it is released to the customer, a total module scan is performed again to not only verify the repair but also to ensure that another DTC was not set during the repair process. The results of this post-scan should also be documented on the repair order so it becomes a part of the documen-tation for the vehicle history. TECH TIP FIGURE 1–9 After checking for stored diagnostic trouble codes (DTCs), the wise technician checks service information for any technical service bulletins that may relate to the vehicle being serviced. STEP 4 CHECK FOR TECHNICAL SERVICE BULLETINS (TSBS) Check for corrections or repair procedures in technical service bulletins (TSBs) that match the symptoms. ● SEE FIGURE 1–9. According to studies performed by automobile manufacturers, as many as 30% of vehicles can be repaired following the information, suggestions, or replacement parts found in a service bulletin. DTCs must be known before searching for service bulletins, because bulletins often include information on solving problems that involve a stored diagnostic trouble code. STEP 5 LOOK CAREFULLY AT SCAN TOOL DATA Vehicle manufacturers have been giving the technician more and more data on a scan tool connected to the data link connector (DLC). ● SEE FIGURE 1–10. Beginning technicians are often observed scrolling through scan data without a real clue about what they are looking for. When asked, they usually reply that they are looking for something unusual, as if the screen will flash a big message “LOOK HERE—THIS IS NOT CORRECT.” That statement does not appear on scan tool displays. The best way to look at scan data is in a definite sequence and with specific, selected bits of data that can tell the most about the operation of the engine, such as the following: ■ ■Engine coolant temperature (ECT) is the same as intake air temperature (IAT) after the vehicle sits for several hours. ■ ■Idle air control (IAC) valve is being commanded to an acceptable range. ■ ■Oxygen sensor (O2S) is operating properly: 1. Readings below 200 mV at times 2. Readings above 800 mV at times 3. Rapid transitions between rich and lean STEP 6 NARROW THE PROBLEM TO A SYSTEM OR CYLINDER Narrowing the focus to a system or individual cylinder is the hardest part of the entire diagnostic process. For example: ■ ■Perform a cylinder power balance test. ■ ■If a weak cylinder is detected, perform a compression and a cylinder leakage test to determine the probable cause. CUSTOMER SATISFACTION FIGURE 1–10 Looking carefully at the scan tool data is very helpful in locating the source of a problem. 8 chapter 1 STEP 7 REPAIR THE PROBLEM AND DETERMINE THE ROOT CAUSE The repair or part replacement must be performed following vehicle manufacturer’s recommendations and be certain that the root cause of the problem has been found. Also follow the manufacturer’s recommended repair procedures and methods. STEP 8 VERIFY THE REPAIR AND CLEAR ANY STORED DTCS ● SEE FIGURE 1–11. ■ ■Test-drive to verify that the original problem (concern) is fixed. ■ ■Verify that no additional problems have occurred during the repair process. ■ ■Check for and then clear all diagnostic trouble codes. (This step ensures that the computer will not make any changes based on a stored DTC, but should not be performed if the vehicle is going to be tested for emis-sions because all of the monitors will need to be run and pass.) ■ ■Return the vehicle to the customer and double check the following: 1. The vehicle is clean. 2. The radio is turned off. 3. The clock is set to the right time and the radio stations have been restored if the battery was disconnected during the repair procedure. CUSTOMER SATISFACTION FIGURE 1–11 Step 8 is very important. Be sure that the cus-tomer’s concern has been corrected. The Case of the No-Start Lexus The owner of a Lexus IS250 had the car towed to a shop as a no-start. The technician discovered that the “check engine” light would not come on even with key on, engine off (KOEO). A scan tool would not com-municate either. Checking the resources on www.iatn. net, the technician read of a similar case where the fuel pressure sensor was shorted, which disabled all serial data communications. The technician disconnected the fuel pressure sensor located on the backside of the engine and the communications were restored and the engine started. The fuel pressure sensor was replaced and the vehicle returned to the happy owner. Summary: • Complaint—The vehicle owner stated that the engine would not start. • Cause—A shorted fuel pressure sensor was found as per a previous similar case. • Correction—The fuel pressure sensor was replaced and this corrected the serial data fault that caused the no-start condition. CASE STUDY Scan tools are the workhorse for any diagnostic work on all vehicles. Scan tools can be divided into two basic groups: 1. Factory scan tools. These are the scan tools required by all dealers that sell and service the brand of vehicle. Examples of factory scan tools include: ■ ■General Motors—Tech 2 or GM MDI ● SEE FIGURE 1–12. ■ ■Ford—New Generation Star (NGS) and IDS (Integrated Diagnostic Software). SCAN TOOLS One Test Is Worth 1,000 “Expert” Opinions Whenever any vehicle has an engine performance or driveability concern, certain people always say: “Sounds like it’s a bad injector.” “I’ll bet you it’s a bad computer.” “I had a problem just like yours yesterday and it was a bad EGR valve.” Regardless of the skills and talents of those peo-ple, it is still more accurate to perform tests on the ve-hicle than to rely on feelings or opinions of others who have not even seen the vehicle. Even your own opinion should not sway your thinking. Follow a plan, perform tests, and the test results will lead to the root cause. TECH TIP THE DIAGNOSTIC PROCESS 9 CASE STUDY The Case of the Rough-Running Impala A customer with a Chevrolet Impala equipped with a 3.4 liter engine is complaining of a running-rough condition and the MIL is illuminated. The customer commented the condition first occurred after a hard acceleration. The technician was able to verify the customer concern. The technician retrieved the codes from the en-gine control module and found a P0306 and a P0300 to be present. Using the graphic misfire counter on the scan tool, the technician was able to confirm that cylinder #6 was consistently misfiring. The technician was able to confirm that both the injector and the ignition coil were operating normally. A compression test of the cylinder #6 revealed compression readings below specifications. A cyl-inder leakage test of cylinder #six showed leakage percentage to be at an acceptable level. The technician removed the valve cover to discover the bolt that held the #6 intake valve rocker arm had pulled out of the cylinder head. ● SEE FIGURE 1–13. The technician was able to repair the bolt hole in the cylinder head with a thread repair kit and reinstall the rocker arm. The technician completed a drive cycle and confirmed the misfire condition was repaired. Summary: • Complaint—The owner complained of a running-rough condition and an illuminated MIL. • Cause—Following the correct diagnostic proce-dure it was determined that the rocker arm bolt had pulled out of the cylinder head. • Correction—The cylinder head was repaired and the rocker arm was reinstalled, which corrected the rough-running concern and turned off the MIL. ROCKER ARM ROCKER ARM STUD FIGURE 1–13 What the technician discovered after removing the valve cover was the root cause of the misfire. ■ ■Chrysler—DRB-III or Star Scan, wiTECH ■ ■Honda—HDS or Master Tech ■ ■Toyota—Master Tech or Tech Stream All factory scan tools are designed to provide bidirectional capability, which allows the service technician the oppor-tunity to operate components using the scan tool, thereby confirming that the component is able to work when com-manded. Also, all factory scan tools are capable of dis-playing all factory parameters. 2. Aftermarket scan tools. These scan tools are designed to function on more than one brand of vehicle while many aftermarket scan tools can display most, if not all, of the parameters of the factory scan tool, there can be a differ-ence when trying to troubleshoot some faults. Examples of aftermarket scan tools include: ■ ■Snap-on (various models including the MT2500 and Modis) ■ ■OTC (various models including Pegasus, Genisys, and Task Master) ■ ■AutoEnginuity and other programs that use a laptop or handheld computer for the display 3. Global (generic) scan tools. Scan tools that read and display just global data are capable of only displaying emission-related information. While global only data is helpful at times, generic scan tools are not usually con-sidered to be suitable for use by professional service technicians. ● SEE FIGURE 1–14. FIGURE 1–12 A TECH 2 scan tool is the factory scan tool used on General Motors vehicles. RETRIEVAL OF DIAGNOSTIC INFORMATION To retrieve diagnostic information from the PCM, a scan tool is needed. If a factory or factory-level scan tool is used, then all of the data can be retrieved. If a global (generic)-only-type scan tool is used, only the emissions-related data can be retrieved. To retrieve diagnostic information from the PCM, use the following steps: 10 chapter 1 Parameter Identification (PID) Scan Tool Parameter Units Displayed Typical Data Value Engine Idling/Radiator Hose Hot/Closed Throttle/ Park or Neutral/Closed Loop/Accessories Off/ Brake Pedal Released 3X Crank Sensor RPM Varies 24X Crank Sensor RPM Varies Actual EGR Position Percent 0 BARO kPa/Volts 65–110 kPa/ 3.5–4.5 Volts CMP Sensor Signal Present Yes/No Yes Commanded Fuel Pump On/Off On Parameter Identification (PID) Scan Tool Parameter Units Displayed Typical Data Value Cycles of Misfire Data Counts 0–99 Desired EGR Position Percent 0 ECT °C>°F Varies EGR Duty Cycle Percent 0 Engine Run Time Hr: Min: Sec Varies EVAP Canister Purge Percent Low and Varying EVAP Fault History No Fault/Excess Vacuum/Purge Valve Leak/ Small Leak/Weak Vacuum No Fault Fuel Tank Pressure Inches of h2O> Volts Varies HO2S Sensor 1 Ready/Not Ready Ready HO2S Sensor 1 Millivolts 0–1,000 and Varying HO2S Sensor 2 Millivolts 0–1,000 and Varying HO2S X Counts Counts Varies IAC Position Counts 15–25 preferred IAT °C/°F Varies Knock Retard Degrees 0 Long-term FT Percent 0–10 MAF Grams per second 3–7 MAF Frequency Hz 1,200–3,000 (depends on altitude and engine load) MAP kPa/Volts 20–48 kPa/0.75–2 Volts (depends on altitude) Misfire Current Cyl. 1–10 Counts 0 Misfire History Cyl. 1–10 Counts 0 Short-term FT Percent 0–10 Start Up ECT °C/°F Varies Start Up IAT °C/°F Varies Total Misfire Current Count Counts 0 Total Misfire Failures Counts 0 FIGURE 1–14 A Bluetooth adapter that plugs into the DLC and transmits global OBD II information to a smart phone that has a scan tool app installed. STEP 1 Locate and gain access to the data link connector (DLC). STEP 2 Connect the scan tool to the DLC and establish communication. NOTE: If no communication is established, follow the vehicle manufacturer’s specified instructions. STEP 3 Follow the on-screen instructions of the scan tool to correctly identify the vehicle. STEP 4 Observe the scan data, as well as any diagnostic trou-ble codes. STEP 5 Follow vehicle manufacturer’s instructions if any DTCs are stored. If no DTCs are stored, compare all sensor values with a factory-acceptable range chart to see if any sensor values are out of range. THE DIAGNOSTIC PROCESS 11 by disconnecting the fuel-injection fuse. Some ve-hicles require that two fuses be disconnected to clear any stored codes. ■ ■Clearing codes—Method 3. If the other two methods cannot be used, the negative battery cable can be dis-connected to clear stored diagnostic trouble codes. NOTE: Because of the adaptive learning capacity of the computer, a vehicle may fail an exhaust emissions test Note: Viewing the PID screen on the scanner is useful in determining if a problem is occurring at the present time TROUBLESHOOTING USING DIAGNOSTIC TROUBLE CODES Pinning down causes of the actual problem can be accom-plished by trying to set the opposite code. For example, if a code indicates an open throttle position (TP) sensor (high resis-tance), clear the code and create a shorted (low-resistance) condition. This can be accomplished by using a jumper wire and connecting the signal terminal to the 5-volt reference ter-minal. This should set a diagnostic trouble code. ■ ■If the opposite code sets, this indicates that the wiring and connector for the sensor is okay and the sensor itself is defective (open). ■ ■If the same code sets, this indicates that the wiring or electrical connection is open (has high resistance) and is the cause of the setting of the DTC. METHODS FOR CLEARING DIAGNOSTIC TROUBLE CODES Clearing diagnostic trouble codes from a vehicle computer sometimes needs to be performed. There are three methods that can be used to clear stored diagnostic trouble codes. CAUTION: Clearing diagnostic trouble codes (DTCs) also will clear all of the noncontinuous monitors. ■ ■Clearing codes—Method 1. The preferred method of clearing codes is by using a scan tool. This is the method recommended by most vehicle manufacturers if the pro-cedure can be performed on the vehicle. The computer of some vehicles cannot be cleared with a scan tool. ■ ■Clearing codes—Method 2. If a scan tool is not available or a scan tool cannot be used on the vehicle being ser-viced, the power to the computer can be disconnected. 1. Disconnect the fusible link (if so equipped) that feeds the computer. 2. Disconnect the fuse or fuses that feed the computer. NOTE: The fuse may not be labeled as a computer fuse. For example, many Toyotas can be cleared Quick and Easy Chrysler Code Retrieval Most Chrysler-made vehicles (Dodge, Ram, and Chrysler) can display the diagnostic trouble code on the dash by turning the ignition switch on and then off and then on three times with the last time being on. This makes it easy for anyone to see if there are any stored trouble codes without having to use a scan tool. ● SEE FIGURE 1–15. TECH TIP Do Not Lie to a Scan Tool! Because computer calibration may vary from year to year, using the incorrect year for the vehicle while using a scan tool can cause the data retrieved to be incorrect or inaccurate. TECH TIP FIGURE 1–15 Diagnostic trouble codes (DTCs) from Chrysler and Dodge vehicles can be retrieved by turning the ignition switch to on and then off three times. Parameter Identification (PID) Scan Tool Parameter Units Displayed Typical Data Value Total Misfire Passes Counts 0 TP Angle Percent 0 TP Sensor Volts 0.20–0.74 Vehicle Speed MPH/Km/h 0 12 chapter 1 DLC LOCATIONS The data link connector (DLC) is a standardized 16-cavity con-nector where a scan tool can be connected to retrieve diagnos-tic information from the vehicle’s computers. The normal location is under the dash on the driver’s side but it can be located within 12 inches (30 cm) of the center of the vehicle. It can be covered, but if it is, then the cover has to be able to be removed without the use of a tool, such as when it is located underneath the ash tray. ● SEE FIGURE 1–16. FIGURE 1–17 A typical OBD-II data link connector (DLC). The location varies with make and model and may even be covered, but a tool is not needed to gain access. Check ser-vice information for the exact location if needed. LEFT CORNER OF DASH NEAR CENTER OF DASH BEHIND ASHTRAY FIGURE 1–16 The data link connec-tor (DLC) can be located in various locations. OBD-II DIAGNOSIS Starting with the 1996 model year, all vehicles sold in the United States must use the same type of 16-pin data link con-nector (DLC) and must monitor emission-related components. ● SEE FIGURE 1–17. Fuel and Air Metering System P0100 Mass or Volume Airflow Circuit Problem P0101 Mass or Volume Airflow Circuit Range or Performance Problem P0102 Mass or Volume Airflow Circuit Low Input P0103 Mass or Volume Airflow Circuit High Input P0105 Manifold Absolute Pressure or Barometric Pressure Circuit Problem if the vehicle is not driven enough to allow the computer to run all of the monitors. CAUTION: By disconnecting the battery, the radio pre-sets will be lost. They should be reset before returning the vehicle to the customer. If the radio has a security code, the code must be entered before the radio will func-tion. Before disconnecting the battery, always check with the vehicle owner to be sure that the code is available. RETRIEVING OBD-II CODES A scan tool is required to retrieve diagnostic trouble codes from most OBD-II vehicles. Every OBD-II scan tool will be able to read all generic Society of Automotive Engineers (SAE) DTCs from any vehicle. THE DIAGNOSTIC PROCESS 13 P0142 O2 Sensor Circuit Problem (Bank 1* Sensor 3) P0143 O2 Sensor Circuit Low Voltage (Bank 1* Sensor 3) P0144 O2 Sensor Circuit High Voltage (Bank 1* Sensor 3) P0145 O2 Sensor Circuit Slow Response (Bank 1* Sensor 3) P0146 O2 Sensor Circuit No Activity Detected (Bank 1* Sensor 3) P0147 O2 Sensor Heater Circuit Problem (Bank 1* Sensor 3) P0150 O2 Sensor Circuit Problem (Bank 2 Sensor 1) P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1) P0152 O2 Sensor Circuit High Voltage (Bank 2 Sensor 1) P0153 O2 Sensor Circuit Slow Response (Bank 2 Sensor 1) P0154 O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1) P0155 O2 Sensor Heater Circuit Problem (Bank 2 Sensor 1) P0156 O2 Sensor Circuit Problem (Bank 2 Sensor 2) P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2) P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2) P0159 O2 Sensor Circuit Slow Response (Bank 2 Sensor 2) P0160 O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2) P0161 O2 Sensor Heater Circuit Problem (Bank 2 Sensor 2) P0162 O2 Sensor Circuit Problem (Bank 2 Sensor 3) P0163 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) P0164 O2 Sensor Circuit High Voltage (Bank 2 Sensor 3) P0165 O2 Sensor Circuit Slow Response (Bank 2 Sensor 3) P0166 O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3) P0167 O2 Sensor Heater Circuit Problem (Bank 2 Sensor 3) P0170 Fuel Trim Problem (Bank 1*) P0171 System Too Lean (Bank 1*) P0172 System Too Rich (Bank 1*) P0106 Manifold Absolute Pressure or Barometric Pressure Circuit Range or Performance Problem P0107 Manifold Absolute Pressure or Barometric Pressure Circuit Low Input P0108 Manifold Absolute Pressure or Barometric Pressure Circuit High Input P0110 Intake Air Temperature Circuit Problem P0111 Intake Air Temperature Circuit Range or Performance Problem P0112 Intake Air Temperature Circuit Low Input P0113 Intake Air Temperature Circuit High Input P0115 Engine Coolant Temperature Circuit Problem P0116 Engine Coolant Temperature Circuit Range or Performance Problem P0117 Engine Coolant Temperature Circuit Low Input P0118 Engine Coolant Temperature Circuit High Input P0120 Throttle Position Circuit Problem P0121 Throttle Position Circuit Range or Performance Problem P0122 Throttle Position Circuit Low Input P0123 Throttle Position Circuit High Input P0125 Excessive Time to Enter Closed-Loop Fuel Control P0128 Coolant Temperature Below Thermostat Regulating Temperature P0130 O2 Sensor Circuit Problem (Bank 1* Sensor 1) P0131 O2 Sensor Circuit Low Voltage (Bank 1* Sensor 1) P0132 O2 Sensor Circuit High Voltage (Bank 1* Sensor 1) P0133 O2 Sensor Circuit Slow Response (Bank 1* Sensor 1) P0134 O2 Sensor Circuit No Activity Detected (Bank 1* Sensor 1) P0135 O2 Sensor Heater Circuit Problem (Bank 1* Sensor 1) P0136 O2 Sensor Circuit Problem (Bank 1* Sensor 2) P0137 O2 Sensor Circuit Low Voltage (Bank 1* Sensor 2) P0138 O2 Sensor Circuit High Voltage (Bank 1* Sensor 2) P0139 O2 Sensor Circuit Slow Response (Bank 1* Sensor 2) P0140 O2 Sensor Circuit No Activity Detected (Bank 1* Sensor 2) P0141 O2 Sensor Heater Circuit Problem (Bank 1* Sensor 2) (continued) 14 chapter 1 P0173 Fuel Trim Problem (Bank 2) P0174 System Too Lean (Bank 2) P0175 System Too Rich (Bank 2) P0176 Fuel Composition Sensor Circuit Problem P0177 Fuel Composition Sensor Circuit Range or Performance P0178 Fuel Composition Sensor Circuit Low Input P0179 Fuel Composition Sensor Circuit High Input P0180 Fuel Temperature Sensor Problem P0181 Fuel Temperature Sensor Circuit Range or Performance P0182 Fuel Temperature Sensor Circuit Low Input P0183 Fuel Temperature Sensor Circuit High Input Fuel and Air Metering (Injector Circuit) P0201 Injector Circuit Problem—Cylinder 1 P0202 Injector Circuit Problem—Cylinder 2 P0203 Injector Circuit Problem—Cylinder 3 P0204 Injector Circuit Problem—Cylinder 4 P0205 Injector Circuit Problem—Cylinder 5 P0206 Injector Circuit Problem—Cylinder 6 P0207 Injector Circuit Problem—Cylinder 7 P0208 Injector Circuit Problem—Cylinder 8 P0209 Injector Circuit Problem—Cylinder 9 P0210 Injector Circuit Problem—Cylinder 10 P0211 Injector Circuit Problem—Cylinder 11 P0212 Injector Circuit Problem—Cylinder 12 P0213 Cold Start Injector 1 Problem P0214 Cold Start Injector 2 Problem Ignition System or Misfire P0300 Random Misfire Detected P0301 Cylinder 1 Misfire Detected P0302 Cylinder 2 Misfire Detected P0303 Cylinder 3 Misfire Detected P0304 Cylinder 4 Misfire Detected P0305 Cylinder 5 Misfire Detected P0306 Cylinder 6 Misfire Detected P0307 Cylinder 7 Misfire Detected P0308 Cylinder 8 Misfire Detected P0309 Cylinder 9 Misfire Detected P0310 Cylinder 10 Misfire Detected P0311 Cylinder 11 Misfire Detected P0312 Cylinder 12 Misfire Detected P0320 Ignition or Distributor Engine Speed Input Circuit Problem P0321 Ignition or Distributor Engine Speed Input Circuit Range or Performance P0322 Ignition or Distributor Engine Speed Input Circuit No Signal P0325 Knock Sensor 1 Circuit Problem P0326 Knock Sensor 1 Circuit Range or Performance P0327 Knock Sensor 1 Circuit Low Input P0328 Knock Sensor 1 Circuit High Input P0330 Knock Sensor 2 Circuit Problem P0331 Knock Sensor 2 Circuit Range or Performance P0332 Knock Sensor 2 Circuit Low Input P0333 Knock Sensor 2 Circuit High Input P0335 Crankshaft Position Sensor Circuit Problem P0336 Crankshaft Position Sensor Circuit Range or Performance P0337 Crankshaft Position Sensor Circuit Low Input P0338 Crankshaft Position Sensor Circuit High Input Auxiliary Emission Controls P0400 Exhaust Gas Recirculation Flow Problem P0401 Exhaust Gas Recirculation Flow Insufficient Detected P0402 Exhaust Gas Recirculation Flow Excessive Detected P0405 Air Conditioner Refrigerant Charge Loss P0410 Secondary Air Injection System Problem P0411 Secondary Air Injection System Insufficient Flow Detected P0412 Secondary Air Injection System Switching Valve or Circuit Problem P0413 Secondary Air Injection System Switching Valve or Circuit Open P0414 Secondary Air Injection System Switching Valve or Circuit Shorted P0420 Catalyst System Efficiency below Threshold (Bank 1*) P0421 Warm Up Catalyst Efficiency below Threshold (Bank 1*) P0422 Main Catalyst Efficiency below Threshold (Bank 1*) P0423 Heated Catalyst Efficiency below Threshold (Bank 1*) P0424 Heated Catalyst Temperature below Threshold (Bank 1*) P0430 Catalyst System Efficiency below Threshold (Bank 2) P0431 Warm Up Catalyst Efficiency below Threshold (Bank 2) THE DIAGNOSTIC PROCESS 15 P0432 Main Catalyst Efficiency below Threshold (Bank 2) P0433 Heated Catalyst Efficiency below Threshold (Bank 2) P0434 Heated Catalyst Temperature below Threshold (Bank 2) P0440 Evaporative Emission Control System Problem P0441 Evaporative Emission Control System Insufficient Purge Flow P0442 Evaporative Emission Control System Leak Detected P0443 Evaporative Emission Control System Purge Control Valve Circuit Problem P0444 Evaporative Emission Control System Purge Control Valve Circuit Open P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted P0446 Evaporative Emission Control System Vent Control Problem P0447 Evaporative Emission Control System Vent Control Open P0448 Evaporative Emission Control System Vent Control Shorted P0450 Evaporative Emission Control System Pressure Sensor Problem P0451 Evaporative Emission Control System Pressure Sensor Range or Performance P0452 Evaporative Emission Control System Pressure Sensor Low Input P0453 Evaporative Emission Control System Pressure Sensor High Input Vehicle Speed Control and Idle Control P0500 Vehicle Speed Sensor Problem P0501 Vehicle Speed Sensor Range or Performance P0502 Vehicle Speed Sensor Low Input P0505 Idle Control System Problem P0506 Idle Control System RPM Lower Than Expected P0507 Idle Control System RPM Higher Than Expected P0510 Closed Throttle Position Switch Problem Computer Output Circuit P0600 Serial Communication Link Problem P0605 Internal Control Module (Module Identification Defined by J1979) Transmission P0703 Brake Switch Input Problem P0705 Transmission Range Sensor Circuit Problem (PRNDL Input) P0706 Transmission Range Sensor Circuit Range or Performance P0707 Transmission Range Sensor Circuit Low Input P0708 Transmission Range Sensor Circuit High Input P0710 Transmission Fluid Temperature Sensor Problem P0711 Transmission Fluid Temperature Sensor Range or Performance P0712 Transmission Fluid Temperature Sensor Low Input P0713 Transmission Fluid Temperature Sensor High Input P0715 Input or Turbine Speed Sensor Circuit Problem P0716 Input or Turbine Speed Sensor Circuit Range or Performance P0717 Input or Turbine Speed Sensor Circuit No Signal P0720 Output Speed Sensor Circuit Problem P0721 Output Speed Sensor Circuit Range or Performance P0722 Output Speed Sensor Circuit No Signal P0725 Engine Speed Input Circuit Problem P0726 Engine Speed Input Circuit Range or Performance P0727 Engine Speed Input Circuit No Signal P0730 Incorrect Gear Ratio P0731 Gear 1 Incorrect Ratio P0732 Gear 2 Incorrect Ratio P0733 Gear 3 Incorrect Ratio P0734 Gear 4 Incorrect Ratio P0735 Gear 5 Incorrect Ratio P0736 Reverse Incorrect Ratio P0740 Torque Converter Clutch System Problem P0741 Torque Converter Clutch System Performance or Stuck Off P0742 Torque Converter Clutch System Stuck On P0743 Torque Converter Clutch System Electrical P0745 Pressure Control Solenoid Problem P0746 Pressure Control Solenoid Performance or Stuck Off P0747 Pressure Control Solenoid Stuck On P0748 Pressure Control Solenoid Electrical P0750 Shift Solenoid A Problem P0751 Shift Solenoid A Performance or Stuck Off P0752 Shift Solenoid A Stuck On P0753 Shift Solenoid A Electrical (continued) 16 chapter 1 P0755 Shift Solenoid B Problem P0756 Shift Solenoid B Performance or Stuck Off P0757 Shift Solenoid B Stuck On P0758 Shift Solenoid B Electrical P0760 Shift Solenoid C Problem P0761 Shift Solenoid C Performance or Stuck Off P0762 Shift Solenoid C Stuck On P0763 Shift Solenoid C Electrical P0765 Shift Solenoid D Problem P0766 Shift Solenoid D Performance or Stuck Off P0767 Shift Solenoid D Stuck On P0768 Shift Solenoid D Electrical P0770 Shift Solenoid E Problem P0771 Shift Solenoid E Performance or Stuck Off P0772 Shift Solenoid E Stuck On Each type of DTC has different requirements for it to set, and the computer will only turn on the MIL for emissions-related DTCs. TYPE A CODES. A type A diagnostic trouble code is emission related and will cause the MIL to be turned on at the first trip if the computer has detected a problem. Engine misfire or a very rich or lean air–fuel ratio, for example, would cause a type A diagnostic trouble code. These codes alert the driver to an emissions problem that may cause damage to the catalytic converter. TYPE B CODES. A type B code will be stored as a pending code in the PCM and the MIL will be turned on only after the second consecutive trip, alerting the driver to the fact that a diagnostic test was performed and failed. NOTE: Type A and Type B codes are emission related and will cause the lighting of the malfunction indicator lamp, usually labeled “check engine” or “service engine soon.” TYPE C AND D CODES. Type C and type D codes are for use with non-emission-related diagnostic tests. They will cause the lighting of a “service” lamp (if the vehicle is so equipped). OBD-II FREEZE-FRAME To assist the service technician, OBD II requires the computer to take a “snapshot” or freeze-frame of all data at the instant an emission-related DTC is set. A scan tool is required to retrieve this data. CARB and EPA regulations require that the controller store specific freeze-frame (engine-related) data when the first emission-related fault is detected. The data stored in freeze-frame can only be replaced by data from a trouble code with a higher priority such as a problem related to a fuel system or misfire monitor fault. NOTE: Although OBD II requires that just one freeze-frame of data be stored, the instant an emission-related DTC is set, vehicle manufacturers usually provide ex-panded data about the DTC beyond that required. How-ever, retrieving enhanced data usually requires the use of an enhanced or factory-level scan tool. The freeze-frame has to contain data values that occurred at the time the code was set (these values are provided in stan-dard units of measurement). Freeze-frame data are recorded during the first trip on a two-trip fault. As a result, OBD-II sys-tems record the data present at the time an emission-related code is recorded and the MIL activated. These data can be accessed and displayed on a scan tool. Freeze-frame data are one frame or one instant in time. They are not updated (refreshed) if the same monitor test fails a second time. REQUIRED FREEZE-FRAME DATA ITEMS. ■ ■Code that triggered the freeze-frame ■ ■A/F ratio, airflow rate, and calculated engine load ■ ■Base fuel injector pulse width ■ ■ECT, IAT, MAF, MAP, TP, and VS sensor data ■ ■Engine speed and amount of ignition spark advance ■ ■Open- or closed-loop status P0773 Shift Solenoid E Electrical OBD-II ACTIVE TESTS The vehicle computer must run tests on the various emission-related components and turn on the malfunction indicator lamp (MIL) if faults are detected. OBD II is an active computer analy-sis system because it actually tests the operation of the oxygen sensors, exhaust gas recirculation system, and so forth when-ever conditions permit. It is the purpose and function of the powertrain control module (PCM) to monitor these components and perform these active tests. For example, the PCM may open the EGR valve momen-tarily to check its operation while the vehicle is decelerating. A change in the manifold absolute pressure (MAP) sensor signal will indicate to the computer that the exhaust gas is, in fact, being introduced into the engine. Because these tests are active and certain conditions must be present before these tests can be run, the computer uses its internal diagnostic pro-gram to keep track of all the various conditions and to schedule active tests so that they will not interfere with each other. OBD-II DRIVE CYCLE The vehicle must be driven under a variety of operating conditions for all active tests to be performed. A trip is defined as an engine-operating drive cycle that contains the necessary conditions for a particular test to be performed. For example, for the EGR test to be performed, the engine has to be at normal operating temperature and decelerating for a minimum amount of time. Some tests are performed when the engine is cold, whereas others require that the vehicle be cruising at a steady highway speed. TYPES OF OBD-II CODES Not all OBD-II diagnostic trouble codes are of the same importance for exhaust emissions. * The side of the engine where number one cylinder is located. THE DIAGNOSTIC PROCESS 17 ■ ■Incorrect oil level or viscosity ■ ■Incorrectly timed timing belt or chain causing valve timing to off but not enough to cause a crank/cam correlation DTC to be set. NO-CODE DIAGNOSTIC STRATEGY If there are no stored DTCs, diagnostic strategy the wise service technician follows includes the following steps: STEP #1: After verifying the customer concern, check vehicle service history and perform a thorough visual inspec-tion checking for the following: ■ ■Evidence of a previous repair or recent body work that may be an indication of an accident (collision). ■ ■Check the fuel for contamination or excessive alco-hol content ■ ■Check that all of the tire sizes are the same, because if they are not, this can cause a vibration that is often confused as being a misfire, especially in four-wheel-drive and all-wheel-drive vehicles. ■ ■Check for evidence of previous service work if the vehicle history is not available that may include engine work such as a timing belt or water pump replacement. ■ ■Check for technical service bulletins (TSBs) that relate to the customer’s concern. STEP #2: Check scan tool data and look at fuel trim numbers. A preferred fuel trim is less than 5% whereas anything less than 10% is considered to be acceptable. A diagnostic trouble code for a rich or lean air–fuel ratio is usually set when the fuel number exceeds 25%. Sometimes drive-ability issues can be experienced by the driver when the exhaust is lean but not lean enough to set a DTC. STEP #3: Perform a test drive using a scan tool set to record the major high-authority sensors in movie mode. The high-authority sensors that should be selected include: ■ ■MAP/MAF ■ ■ECT/IAT ■ ■TP sensor ■ ■O2 sensors The TP and MAF sensor should track each other, and when shown using the graphing capability on the scan tool, they show a direct relationship to each other as the vehicle is accelerated. Any sensor that shows to be not responding during engine load test needs to be checked more thoroughly. STEP #4: If the root cause has not been located, perform a five-gas analysis of the exhaust gases. See Chapter 26 for details regarding what the results may indicate. STEP #5: Using all available resources, including vehicle manu-facturer’s recommended testing procedures, determine the root cause of the problem. After making the repair, ■ ■Short-term and long-term fuel trim values ■ ■For misfire codes—identify the cylinder that misfired NOTE: All freeze-frame data will be lost if the battery is disconnected, power to the PCM is removed, or the scan tool is used to erase or clear trouble codes. DIAGNOSING INTERMITTENT MALFUNCTIONS Of all the different types of conditions that you will see, the hardest to accurately diagnose and repair are intermittent malfunctions. These conditions may be temperature related (only occur when the vehicle is hot or cold), or humidity related (only occur when it is raining). Regardless of the conditions that will cause the malfunction to occur, you must diagnose and correct the condition. When dealing with an intermittent concern, you should deter-mine the conditions when the malfunction occurs, and then try to duplicate those conditions. If a cause is not readily apparent to you, ask the customer when the symptom occurs. Ask if there are any conditions that seem to be related to, or cause the concern. Another consideration when working on an OBD-II-equipped vehicle is whether a concern is intermittent, or if it only occurs when a specific diagnostic test is performed by the PCM. Since OBD-II systems conduct diagnostic tests only under very precise conditions, some tests may be run only once during an ignition cycle. Additionally, if the requirements needed to perform the test are not met, the test will not run during an ignition cycle. This type of onboard diagnostics could be mistaken as “intermittent” when, in fact, the tests are only infrequent (depending on how the vehicle is driven). Examples of this type of diagnostic test are HO2S heaters, evaporative canister purge, catalyst efficiency, and EGR flow. When diag-nosing intermittent concerns on an OBD-II-equipped vehicle, a logical diagnostic strategy is essential. The use of stored freeze-frame information can also be very useful when diag-nosing an intermittent malfunction if a code has been stored. NO-CODE DIAGNOSIS POSSIBLE CAUSES No-code diagnosis is what the service technician needs to perform when there is a customer concern but there are no stored diagnostic trouble codes (DTCs). This type of customer complaint often results in a potential long process to locate the root cause. There are many possible causes of a problem such as a hesitation, stalling of poor performance that will not cause a DTC to set. Some of the possible causes include: ■ ■Alcohol (ethanol) in high concentrations in the fuel ■ ■Contaminated fuel that has water or diesel fuel mixed with the fuel ■ ■Clogged air intake systems due to an animal nest of road debris caught in the air intake system ■ ■Partially clogged or restricted exhaust system ■ ■Engine mechanical fault such as recessed valves into the cylinder head resulting in reduced valve lift, thereby reducing engine power. 18 chapter 1 verify the repair by performing a test-drive under similar conditions that caused the customer concern to make sure that the cause has been successfully repaired. DETERMINING ROOT CAUSE OF REPEATED COMPONENT FAILURES THE FIVE WHYS Typically when a component or system fails multiple times, the root cause of the failure was not corrected. When diagnosing the root cause of repeated component or system failure, the wise technician asks why five times. For example, for a case where the PCM set repeated P0017 (CKP/CMP correlation) DTCs, the oil control valve was replaced and the DTC cleared. According to the repair forums, this was a common repair for this condition. The engine The Case of the No-Power Kia A customer had a Kia Sorento towed to a shop be-cause it would not accelerate and the engine would not increase in speed higher than 1000 RPM. No diagnostic trouble codes were found and no technical service bulletins were found that pertained to this con-dition either. The data display on the scan tool did not show anything out of range and a through visual in-spection found that the engine appeared to well main-tain without any obvious or visible faults. Then another technician in the shop told the technician working on the vehicle that the brake lights were on whenever the engine was running even though no one was in the vehicle. This led to a closer examination of the brake switch, and when it was moved the engine was then able to be accelerated normally. A replacement brake switch was installed and the problem of a lack of ac-celeration was solved, and after replacement, the ve-hicle performed normally. The customer was pleased that a simple and low-cost solution was found. Summary: • Complaint—The vehicle owner complained that the engine would not accelerate and the engine speed would not increase higher than 1000 RPM. • Cause—A defective brake switch caused the PCM to sense that the brake was applied and limited engine speed. • Correction—A replacement brake switch fixed the problem and allowed the vehicle to accelerate normally. CASE STUDY The Brake Pedal Trick If the vehicle manufacturer recommends that battery power be disconnected, first disconnect the nega-tive battery cable and then depress the brake pedal. Because the brake lights are connected to battery power, depressing the brake pedal causes all of the capacitors in the electrical system and computer(s) to discharge through the brake lights. TECH TIP appeared to be operating correctly; however, the check engine light with the same code occurred again after a week? Why? Why #1: The technician did not complete a thorough diagnosis, instead relying on a silver bullet in a repair forum. On the second attempt to repair the vehicle the technician followed the diagnostic procedure for the code. The resistance of the new oil control valve was found to be within specifications. The camshaft position (CMP) sensor was tested based on the advice from another technician. The sensor passed all the diagnostic tests and appeared to be generating a normal signal. Why #2: If the oil control valve and the sensor are both good, why did the code reset? The technician checked all of the wiring and the electrical connectors and found them to be okay. Why was the problem still occurring? Why #3: During a subsequent test drive, the code set again. This time the technician tested the crankshaft sensor and verified the condition of the timing belt. Each of the components tested normally. Why #4: The technician thought that the recurring problem was related to the OCV because when these were replaced, it fixed the vehicle for some time. The tech-nician then noticed the engine oil was low and very dirty. Why was this important? Why #5: Understanding that clean oil was needed for the sys-tem to operate properly, the engine oil and filter were replaced making sure to use the oil recommended by the manufacturer and an oil filter that met original equipment specifications. The code was cleared and on subsequent test drives the failure did not reoccur. On the second repair attempt the technician followed the diag-nostic process to a logical end. No assumptions were made, but instead decisions were made based on the test results. In the end, the root cause of the problem was actually very simple and the repair was relatively inexpensive. MULTIPLE COMPONENT FAILURE DIAGNOSIS If more than one component is found to be defective, the root cause has to be found. If the components are electrical, use a wiring diagram and check for the following: ■ ■Do the components share a common ground connec-tion? If so, this could be the most likely cause and the first place to check. THE DIAGNOSTIC PROCESS 19 ■ ■Do the components share the same power? If so, then this could be the source of common component failure. ■ ■Are the components or wiring near a heat source such as the exhaust system or EGR system components? Heat can cause electrical issues and often cause issues with more than one component. ■ ■Are the components or wiring near something that is moved such as a door, hood, or trunk (tailgate) open-ing? The movement can cause electrical issues and often cause issues with more than one component. ■ ■Follow the diagnostic strategy to find and correct the root cause, then verify the repair has solved the customer concern before returning the vehicle. Each vehicle manufacturer has established their own diagnos-tic routines and they should be followed. Most include the fol-lowing steps: STEP 1 Retrieve diagnostic trouble codes. STEP 2 Check for all technical service bulletins that could be related to the stored DTC. STEP 3 If there are multiple DTCs, the diagnostic routine may include checking different components or systems in-stead of when only one DTC was stored. STEP 4 Perform system checks. STEP 5 Perform the necessary service or repair STEP 6 Perform a road test matching the parameters re-corded in the freeze-frame to check that the repair has corrected the malfunction. STEP 7 Repeat the road test to cause the MIL to be extinguished. NOTE: Do not clear codes (DTCs) unless instructed by the service information. Following the vehicle manufacturer’s specific diagnostic routines will ensure that the root cause is found and the repair verified. This is important for customer satisfaction. MANUFACTURER’S DIAGNOSTIC ROUTINES VERIFYING THE REPAIR PROCEDURE After the repair has been successfully completed, the vehicle should be driven under similar conditions that caused the original concern in order to verify that the problem has been corrected. To perform this test drive, it is helpful to have a copy of the freeze-frame parameters that Drive the Light Out If working on a vehicle that is subject to state emis-sion testing, it is best to not clear codes. When diag-nostic trouble codes are cleared, all of the monitors have to be rerun and this can be a time-consuming job. Instead of clearing the code, simply drive the vehicle until the PCM clears the code. This will likely take less time compared to trying to drive the vehicle under varying conditions to run all of the monitors. TECH TIP were present when the DTC was set. By driving under similar conditions, the PCM may perform a test of the system and automatically extinguish the malfunction indicator light (MIL). This is the method preferred by many vehicle manufacturers. OBD MONITORS FOR REPAIR VERIFICATION All 1996 and newer vehicles perform enhanced diagnostic checks of specific emission control components such as engine, transmission, fuel systems, and other emissions controls. Each diagnostic check communicates with the powertrain control module’s (PCM) diagnostic executive to record the data in the readiness monitor. These diagnostic checks are generally performed while the vehicle is driven in a specific manner and are a great way to prove the repair was successful. If the diagnostic checks have been performed and passed, the PCM marks them as “ready.” Technicians in a non-emissions test area are able to use the data to ensure the vehicle is repaired and that no other codes are set prior to returning the vehicle to the customer. For technicians who work on vehicles in an emission test area this is an important step in the repair process. If diagnostic data has been erased during vehicle repairs or through battery disconnection, the PCM will flag the monitors as “incomplete” or “not ready.” Vehicles are rejected from emission testing when these diagnostic checks are not completed. The number of monitors allowed to be not complete depends on the year of the vehicle and the emission testing area requirements. The vehicle performs the self-diagnostic tests when the vehicle is driven, referred to as a “drive cycle.” Therefore, after the repair is complete the vehicle will need to be driven through a drive cycle. If the check engine light does not turn off, then addi-tional repair(s) may be required. If the repairs require the DTCs to be cleared or a battery disconnect (which also clears DTCs), then the vehicle needs to be driven to get the monitors to run and pass. ROAD TEST (DRIVE CYCLE) Use the freeze-frame data and test-drive the vehicle so that the vehicle is driven to match the conditions displayed on the freeze-frame. If the battery has been disconnected, then the vehicle may have to be driven under conditions that allow the PCM to 20 chapter 1 DIESEL OBDII MONITOR READINESS PRIOR TO START ■ ■Fuel level greater than 25%. ■ ■Coolant temperature below 140°F (60°C) ■ ■Battery voltage must be between 11 and 16 volts. PTO is not engaged TO RUN THE MONITORS 1. Allow the engine to idle for a minimum of two minutes and warm the engine to greater than 140 degrees. (Vehicle must be stationary and the accelerator must not be depressed during this time.) 2. Drive for 5 minutes at speeds above 25 mph and less than 45 mph (in-town driving). 3. Drive the vehicle at highway speeds and perform 10−15 zero fueling events (decelerate for 10 seconds with foot off of accelerator). 4. Drive the vehicle at highway speeds and perform 15−20 boost events (sudden depression of the accelerator pedal to provide turbocharger boost to the system). 5. Drive the vehicle at highway speeds in a steady state for 12−15 minutes. 6. Return to the shop and let vehicle idle for 30 seconds. 7. With the vehicle in park increase the engine speed to 1200−1300 RPM for 2−3 minutes (repeat 3−4 times). 8. Let idle for 30 seconds. 9. Shut off vehicle. 10. Cycle key back on and check readiness status. 1. Funnel diagnostics—Visual approach to a diagnostic procedure: Step 1 Verify the problem (concern) Step 2 Perform a thorough visual inspection and basic tests Step 3 Retrieve the diagnostic trouble codes (DTCs) Step 4 Check for technical service bulletins (TSBs) Step 5 Look carefully at scan tool data Step 6 Narrow the problem to a system or cylinder SUMMARY Step 7 Repair the problem and determine the root cause Step 8 Verify the repair and check for any stored DTCs 2. A thorough visual inspection is important during the diag-nosis and troubleshooting of any engine performance problem or electrical malfunction. 3. If the MIL is on, retrieve the DTC and follow the manufac-turer’s recommended procedure to find the root cause of the problem. 4. OBD-II vehicles use a 16-pin DLC and common DTCs. 8. Repeat steps 6 and 7 five times. 9. Using scan tool, check readiness. conduct monitor tests. This drive pattern is called a drive cycle. The drive cycle is different for each vehicle manufacturer but a universal drive cycle may work in many cases. In many cases performing a universal drive cycle will reset most monitors in most vehicles. UNIVERSAL DRIVE CYCLE PRECONDITIONING: Phase I. MIL must be off. No DTCs present. Fuel fill between 15% and 85%. Cold start - Preferred = 8 - hour soak at 68°F to 86°F. alternative: ECT = IaT. 1. With the ignition off, connect scan tool. 2. Start engine and drive between 20 and 30 mph for 22 ­ minutes, allowing speed to vary. 3. Stop and idle for 40 seconds, gradually accelerate to 55 mph. 4. Maintain 55 mph for 4 minutes using a steady throttle input. 5. Stop and idle for 30 seconds, then accelerate to 30 mph. 6. Maintain 30 mph for 12 minutes. 7. Repeat steps 4 and 5 four times. Using scan tool, check readiness. If insufficient readiness set, continue to universal drive trace phase II. Important: (Do not shut off engine between phases). Phase II: 1. Vehicle at a stop and idle for 45 seconds, then accelerate to 30 mph. 2. Maintain 30 mph for 22 minutes. 3. Repeat steps 1 and 2 three times. 4. Bring vehicle to a stop and idle for 45 seconds, then accelerate to 35 mph. 5. Maintain speed between 30 and 35 mph for 4 minutes. 6. Bring vehicle to a stop and idle for 45 seconds, then accelerate to 30 mph. 7. Maintain 30 mph for 22 minutes. THE DIAGNOSTIC PROCESS 21 REVIEW QUESTIONS 1. Why should TSBs be checked after retrieving diagnostic trouble codes? 2. Why does the customer concern need to verified? 3. What is the difference between an aftermarket scan tool and a factory-level scan tool? 4. What is the preferred method to use to clear DTCs? 5. What is the definition of a trip? CHAPTER QUIZ 1. Technician A says that the first step in the diagnostic pro-cess is to verify the problem (concern). Technician B says the second step is to perform a thorough visual inspec-tion. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor B 2. Which item is not important to know before starting the diagnosis of an engine performance problem? a. List of previous repairs b. The brand of engine oil used c. The type of gasoline used d. The temperature of the engine when the problem occurs 3. A generic (global)-type scan tool can retrieve ____________ data. a. emissions-related b. HVAC c. ABS brake system d. All of the above 4. The steps in a manufacturer-specific diagnostic routine are being discussed. Technician A says that after record-ing any DTCs, the codes should be erased. Technician B says to road test the vehicle twice to turn off the MIL. Which technician is correct? a. Technician A only b. Technician B only c. Both technicians are correct d. Neither technician is correct 5. Technician A says that if the opposite DTC can be set, the problem is the component itself. Technician B says if the opposite DTC cannot be set, the problem is with the wiring or grounds. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor B 6. The preferred method to clear diagnostic trouble codes (DTCs) is to ____________. a. disconnect the negative battery cable for 10 seconds b. use a scan tool c. remove the computer (PCM) power feed fuse d. cycle the ignition key on and off 40 times 7. Which is the factory scan tool for Chrysler brand vehicles equipped with CAN? a. wiTECH b. Tech 2 c. NGS d. Master Tech 8. What fault could occur that can cause a driveability issue and not set a diagnostic trouble code (DTC)? a. Alcohol (ethanol) in high concentrations in the fuel b. Contaminated fuel that has water or diesel fuel mixed with the fuel. c. Clogged air intake systems due to an animal nest of road debris caught in the air intake system d. Any of the above 9. Technician A says that knowing if there are any stored di-agnostic trouble codes may be helpful when checking for related technical service bulletins. Technician B says that only a factory scan tool should be used to retrieve DTCs. Which technician is correct? a. Technician A only b. Technician B only c. Both Technicians A and B d. Neither Technician A nor B 10. A drive cycle is designed to reset all the OBD-II moni-tors. Before starting the drive cycle the engine should be ____________. a. fully warmed up (cooling fans cycled on and off two times) b. have a full tank of fuel c. cold (ECT = IaT) d. operated at idle for two minutes