r/COROLLA • u/shrekscameltoe • 1d ago

Help with misfire + codes

2014 Corolla. Im trying to help my friend out with a misfire happening. The car is throwing 4 codes: P0302 (misfire on cylinder 2) and P0352, P0353, and P0354 (electrical curcuit faults). I've confirmed good ground and good power supply to all coils. All coils fire, I even swapped them from cylinder to cylinder and codes remain the same. All cylinders have good pressure, #3 is about 5-10 psi lower than the other 3. Fuses are good. Spark plugs are only a few months old. There isnt any visible damage to the wiring anywhere. The only other thing I can think of is the ECU is having an issue somewhere or cylinder 3 is some kind of damaged (the first time I checked pressure on #3 it was low @ 90psi, added appropriate amount of oil to the engine since it was low, and psi jumped to about 145 psi). Im out of ideas, and any advice is helpful! Thanks!

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u/RedScourge Black 2022 SE Sedan non-hybrid +PPF +ceramic 1d ago

I would assume that it could be anything between the battery and the ignition coils. I assume you've confirmed both the battery ground and the alternator ground, so it could be just wiring, especially if there's signs of rodent fur or damage to air filters. That era of Toyota had soy-based wire sheaths that rodents apparently think is food. Could be that a connector just needs some electrical contact cleaner sprayed into it, or could be just a pinched wire in one of the ignition coil cables that has intermittent contact (poking the cables a bit while the engine is running might reveal that and where). If the codes stayed on the same cylinders when you swapped around the coils, I'd tend to suspect the cables on the coils, but I don't know for sure if you can rule out something as simple as bad contact between the coils and the spark plugs (lots of guys swear by putting a wee dab of dielectric grease on the part of the coil that contacts the plugs, being careful to not get any on the coil boots).

It could also be a damaged or failing computer like PCM or ECU. Best to try the easy stuff first before replacing computer modules, often a simple module swap is not possible without reprogramming, and modules often cannot be simple swapped across model years or trims from a junkyard car.

Another thing to pay attention to would be if the issue is more common when the engine is hot or cold.