Diagnosing and Fixing P0303 Cylinder 3 Misfire Code

welcome to Andy's Garage I'm Andy Phillips today we're going to be diagnosing and fixing a p0303 engine code so let's go ahead and get started now first we need to understand what the code is the p0303 now anytime that you're getting any of the 300 series whether it be the P0 300 beyond that those are usually dealing to misfires in your cylinders if you're getting to P 0300 that's a random misfire those are a little bit trickier to diagnose because it's not specific so you got to do more when you're getting in the case here we have the p0303 that 03 that's cylinder number three so if you have a p03 0 1 that's cylinder 1 P 0302 cylinder 2 and so forth so that's easier because this one's telling us specifically the problem is with cylinder three now what we're going to be doing this video is diagnosing what it could be it could be your ignition coil pack it could be your spark plugs it could be your spark plug wires there there's a few things that it could be you don't just want to be throwing money at it you want to diagnose it properly and replace the part so what we're going to do I'm going to kind of show you what the vehicle was doing I was driving on the highway went to accelerate to merge and kind of had a little bit of like a kind of like a not a cough but a little bit of a hiccup to it and then it was kind of sluggish so I was like okay something's not right check engine light kind of blinked a couple times and went out okay so that was cool driving everything seemed fine so I had a feeling it might be a misfire so I decided to accelerate to test it again and as soon as I went to accelerate it was like it was kind of skipping a little bit definitely the the indication of a misfire and then the check engine light flashed a couple more times and then came on in St on at that time I brought it back we did a diagnostic on it so I'm going to show you right now I'm going to start the car unfortunately it might not be able to manifest as clearly as it did when I was driving it on the video but let's take a look we're going to start it up and see what it looks like and then I'm going to connect the diagnostic reader to it so we can take a look at it and I'll show you the code that we're getting you can see our check engine light on let's connect our diagnostic reader here check our fault codes and see what we're looking like okay so we have a lot of stuff going on here you can see here we have our p0303 misfire detected it also through a random misfire as well which sometimes it can do that but it's pinpointing to three and then we see a couple other ones here in a pending status but um we're going to I'm going to clear these out and then I'm going to show you what we're going to do to pinpoint the cylinder 3 and then we'll also look at some of the other ones okay we clear it let's see all right so everything is clear we're going to start the car now check engine light is out so that's good so we know it's clear [Music] okay so the first thing we're going to do let's pop this engine cover off these things just get in the way move that out of the way now this this particular vehicle is very easy and I'll get a closeup because you have individual ignition coil pack so for cylinders 1 2 3 and four you have one ignition coil pack that goes down the spark plug and then it just connects to a harness and that's it some Vehicles it's not as easy as shown here this particular vehicle has one IGN I coil pack and then you have the spark plug wires all feeding into it and then on this older vehicle you have the distributor cap as you can see there and then you have these spark plug wires going from that to the individual spark plugs so with this one what we're going to do we know that cylinder 3 is the one that it's showing is the issue even though there's some other Penning ones going on as well could be spark plugs but an easy way to test this is I'm going to take our cylinder 3 ignition coil pack we're going to move it to cylinder 1 if our code goes from p0303 to P0301 we know that it's the ignition coil pack if it stays on cylinder 3 we're going to check the spark plugs because it could be that as well so let's move this one over and then we're going to go ahead and run the engine and then see what it looks like when it generates the next code and these right here are our ignition coil packs just held on with one little bolt and that's it they pop right up so cylinder 1 2 3 and four is right back here so if you have a newer that's like this is makes it very easy as opposed to what we looked at on the other vehicles now on some Vehicles you may have an ignition coil pack like this but instead of just this harness you may still have the spark plug wire connecting to the spark plug as seen here this particular General Motors vehicle has these individual ignition coil packs you can see here it's a V8 so four on each side but then from it you have individual spark plug wires running from that to the spark plugs this one is easier because this itself the ignition coil pack slides right over the spark plug itself so it's pretty simple to diagnose this type always start with disconnecting your negative off your battery um because since you're dealing with the electric there you don't want to cause any shorting out so we'll get this off here slide that off here I probably should clean that a little bit but slide that off here to the side Slide the harness off cylinder three do cylinder one pop it out and that's where it connects right here to the spark plug that's why you don't have the the spark plug wires so we'll move this one to here swap them out put this one here I'm going to secure everything plug them back in and then we'll be back to start the vehicle and see if the misfire moved to 301 from 303 let's start it up okay light is out it is a little bit a little bit you can feel the misfire a little bit there is no check engine light that has come on so I'm going to take it for a spin and see if we can't get it to trigger anything I'm accelerating and you can feel the misfires I don't know if you can see the light flashing there we're definitely getting a misfire and it it'll start to take off and then it'll HIC up and see the light went out and let's see if I can get it to do it again hang on one second ready to open it up again see you can feel a misfire and the car is jolting a little bit let's take it back and connect the diagnostic and see what it's saying now this this is an easy way to tell if you're at a slower standstill you accelerate yeah the car is it's kind of sputtering and struggling to get up the RPM definitely misfiring let's rescan it and see okay well you can see now the code is P0301 we were at the p0303 we did move the the coil pack to cylinder 1 and it definitely the misfire traveled with it so let's wait for it to finish at 100% make sure there's nothing else but right now that's clearly showing what the issue is all right so everything is done and there it is we have the P0300 the randomness fire which a lot of times can accompany a specific one but it's definitely on cylinder one well that's easy because we know that that coil pack needs to be replaced so what I'm going to do now we're going to replace that one that's now been moved to cylinder one however and I know these can be costly and sometimes in your budget you can only replace the one that's faulty but it's a very very good idea and highly recommended if you're going to be replacing one of them do all of them because there's a very good chance if that one failed the other ones are getting ready to do it as well so while you have it here take care of all of them I'm going to replace all four of them but for this video I just wanted to show the DI the the the process of diagnosing it which is that so we are going to replace that one and then for this video we're going to see if that corrects our problem we'll take it for Drive see how that is but I'm also going to check the spark plugs too because I don't know how old the spark plugs are in this vehicle they may be in need of being replaced as well so we're going to check those as well because while you're doing this work here with a coil pack or if the coil pack wasn't the issue like let's say with moving that it was still showing cylinder 3 we would check the spark plugs anyway so while we have this here let's make sure we have good spark plugs all new coil packs that way all that's taken care of so I'm going to disconnect the battery again again we're going to take cylinder one out and be careful the temperature because like in the case here we just drove this thing so this is still going to be hot you don't want to get burned so set that off to the side get that off this coil pack is definitely the bad one so I'm going to get the new one we're going to put it in and then we'll take it for a drive we'll clear the codes and see how everything is this is the one that came out um here's our new one we'll drop that in push it all the way down you want to get a nice secure fit there we go put this screw it in next thing I'm going to do that's in let's take it for a drive take it for a drive see if that solved the problem we're going to clear the the uh the ECU so we have a clear slate and then when we come back I'm going to check the spark plugs anyway probably not a bad idea to swap all that stuff out like I said we are going to do all the coil packs we'll reconnect and then we're going to clean everything clear everything off okay we'll clear it no check engine light everything is clear let's take a first Spin and then we'll check it again okay let's accelerate nice and smooth no sputters the RPM's ramped up very fast no check engine light flashing let's drive a little bit more and make sure let's open it up a little bit more come down here take a look accelerating very good nice and smooth once again no blinking lights or anything so we're going to drive a little bit more then we're going to head back to the garage connect it and see what the diagnostic reader says if there's anything that was pending or any issues it's driving very smooth definitely no misfires I think we solved it let's refresh this and let's see what it comes up with nothing okay no fa codes logged into ECU after that drive everything ran well as we saw it when we checked the ECU normally we were generating misfires in cylinder 3 and then one when we moved it now everything is taken care of so as far as diagnosing this misfire on this vehicle and fixing it that's it by moving the ignition coil pack from the cylinder it was pinpointing moving it to another cylinder if it's the coil pack it's going to go with it as it did in this case it moved to cylinder one that's been solved but as mentioned already highly recommended you replace all of them because there's a very good chance the other ones are going to start to fail so I'm going to replace those but let's also take a look at the spark plugs because those can also be contributing to it as well or in the case where the cylinder 3 did not move with the coil pack check spark plugs but this is a good opportunity for me to replace the spark plugs anyway cuz this vehicle's older and I don't remember when the last time they were replaced so I'm going to take those off we'll check them out swap those out in the coil packs and then wrap up this video all the ignition coil packs have been removed and if we look down in there you can see the spark plugs we're going to remove those now and inspect those and replace them if needed removing our first one here cylinder 1 take a look at that and see what that shows us all right let me get a closeup you can see it's not terrible I've seen some a lot worse but either way definitely uh going to replace it while we're in here if we're going to swap out that one coil pack as mentioned already we'll do the rest of them and then get these taken care of as well that way we get all this changed out for performance and fuel economy things like that we want this vehicle running uh as best as it can up here is everything that came off the vehicle you can see the spark plugs these are the ignition coil packs this is cylinder 3 the bad then here's the new ones that are going on lined up here but just to show you real quick a comparison this is the spark plug coming off the gap on this particular vehicle should be around 031 to 04 these are coming in around 060 because they're so deteriorated and then here's the new one here let me clear that up so definitely not a bad idea replace all this like I said if it's in your budget if not just do the one coil pack since we diagnosed that was the issue but I'm going to put all this in and then we'll wrap this up now it's important if you do decide to change out your spark plugs when when you're taking care of your uh ignition coil packs it's important that you torque them properly I'll have a link across the top on how to uh torque spark plug spark plugs I also have links down in the description about using a torque wrench things like that another thing that's important is you want to make sure that you get the proper gapping spec for your vehicle for your spark plugs if you want to see a video I did on how to gap spark plugs I'll also have that link across the top down in the description but let's torque these now make sure they're to the right torque you can hear that they're good move on to the other ones and then we'll put the coil packs in everything has been replaced and put back we have the new ignition coil packs the new spark plugs gapped properly torqued properly everything is reconnected so let's start up this engine and uh check everything [Applause] out just got back from driving it and we'll check here the actual misfires on each cylinders so if we look here cylinder 1 zero counts we move down here to cylinder 2 zero misfire counts on that as well if we go down to cylinder 3 you can see also zero counts and then down here at the bottom is cylinder 4 same thing zero misfire counts everything looks great everything is running great as we saw so just to recap as we wrap up this video we had the p0303 engine code which is a misfire on cylinder 3 what we did to diagnose it is we took the coil pack from cylinder 3 moved it to one cleared the computer took it for a drive got misfires again when we checked it now it was showing was on cyinder one so that pinpointed the fact that the issue was the coil pack if it wasn't going to do that then we would be checking the spark plugs and as we saw here we did them anyway while we had all this off and they needed to be replaced anyway but that would be your next step or if you have a vehicle as we saw earlier where you have a distributor cap where you have spark plug spark plug wires or even if you have uh coil packs but you still have the spark plug wires if the packs are not the issue then next you want to be checking the spark plugs or spark plug wires if you want to see a video I did on how to check resistance on spark plug wires you can check that out via the link above I also have that down in the description but as far as for this video diagnosing the misfire on cylinder 3 and fixing it that wraps up this video please send me any questions and comments I would love to hear from you I hope that this video was informative for you helped you with anything that you're working on as men mention already if you are in the situation as we were here highly recommended you change out all your coil packs check the spark plugs if it's in your budget if it's not your budget then just replace that one coil package just you're taking a little bit of a gamble but please like the video subscribe to the channel and I'll see you next time