Been reading thread after thread of cars with misfire codes P0300, P0301, p0302, doesn't seem like a single one has ever posted a resolution, and while "clean EGR, cooler, intake etc.." is the most common suggestion, it rarely solves the problem. I'm getting these codes about once a week (always all three at the same time) and my engine pretty much always runs rough at low RPM. I cleaned the EGR, cooler, pipe, and intake and replaced the plugs about 20,000 miles ago. Has anyone full stop solved those codes with a EGR etc. cleaning? Anyone ever come to a different resolution on the p0300, p0301, p0302 code problem?
I'm thinking, unfortunately, once you get to that point, a fully blown head gasket is usually what comes next. I was throwing occasional misfire codes for a few months before mine went. Hope this isn't your fate, but keep an eye on the antifreeze level.
No coolant loss whatsoever, luckily. I do get minor oil loss, which possibly coincides with when the issue began (it sort of crept up slowly). It's only like 1/2 to 1 quart every 5,000mi. Previous oil changes had no oil loss. Fully expecting worse case scenario, it's just kinda frustrating that from so many posts there's basically no resolutions. Would be happy to install and oil catch can or clean, EGR, intake, throttle body, I just don't want to do the work only to have a bad engine. I would also be happy to take it to a mechanic I'm just not confident they will/can properly diagnose it, which seems like a theme to some of these threads as well. Should I swap the injectors to rule that out? Guess I just need some advice or a push in some direction for my next action.
I just remedied this issue with replacing the spark plugs and resetting the CEL. EGR & intake manifold was cleaned roughly 50k miles ago. Also installed a new 12V battery because Carista notified me the voltage was low and I read on a thread that might’ve contributed to misfires as well.
Cool thanks. I think I will try spark plugs, I bought mine cheap off ebay from a US seller, but the packaging indicated that they came from China. Do those get counterfeit? I'm tempted to just put the old ones back in as I still have them, but I did get some rough idling (like once or twice ever) with no codes back on the old plugs, so I am not that optimistic. In one thread a guy mentions possible worn lower engine bearing from low oil instances, anyone ever had that happen? Never had a low oil instance, but I bought my car used.
China, the great copier of the world. I learned my lesson several years ago when I got burned on a micro SD card from China. I vowed, never again. Denso are having counterfeit issues. They look very similar to the originals. Have you tried swapping the coils?
I will try the coils later today. For some reason hadn't considered how easy that is, should have done it a while ago.
Always start from the easiest solutions and work your way up. You've got a lot of room to work with until you need a new engine. You can't see it but my fingers are crossed this works for you.
135,000 miles I swapped the coils last night and just got a CEL now, strangely enough it's just a p0301. Does that tell me anything? I think every single other time I've had all three codes (0300 0301 and 0302) simultaneously. I'm not sure how the cylinder numbers work but looking at the engine from the front of the car and going left to right 1-4, I swapped 1 and 2 with 3 and 4 respectively. So I don't feel real confident it's a coil thing, but it still seems strange. I think I'm going to replace the new plug with the old ones tonight and go from there.
I haven’t seen a counterfeit Denso plug yet but I think I’m just lucky. I've seen fakes of several other prominent brands now. Be careful.
Head gasket failure always seems to be between cylinders 1 and 2. Standing at the front of the engine bay, cylinder one's at the left end.
Ironic that you just posted that! Swapped the plugs just now with the old ones I had. (full disclosure: I have a lexus ct200h so plug swap is much quicker) They looked awful, the tips were worn down twice as much as the tips on my old ones, which I only assume had 110,000 miles on them. So far engine is running smooth... So happy. I must've got some fakes, I'll be damned. Is there any reason to believe I didn't get fake plugs and something could be causing them to wear prematurely? Don't want to get to excited yet.
if you open it up to all the possibilities? Coils installed wrong… a few times?? then suddenly right? Nope. New plugs installed wrong, but the the old ones suddenly correctly? Mmm.. Nooope. Yeah these were bum plugs. I can’t say they were counterfeit, but they sure weren’t right.
I think we found your problem. Do a quick Google search 'Denso counterfeit'. There were even some instances in which dealerships, allegedly, sold fake plugs to customers. Happy to read you're back up and running.
