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Ignition & Misfire Trouble Codes: List & Fixes

P03xx codes cover misfires and the sensors the engine needs to time ignition. P0300 means random or multiple misfires; P0301 to P0312 name the cylinder that is misfiring; crankshaft and camshaft position sensor codes also sit in this range. On coil-on-plug engines, swapping the coil from the misfiring cylinder with a neighboring one and seeing whether the misfire follows is a quick, cheap first test. If the check engine light is flashing, reduce load and get the car checked promptly to protect the catalytic converter.

66Codes
3.0Average severity
15%High or critical
12%DIY-friendly
Severity distributionSeverity distribution

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P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High P0301 Powertrain Cylinder 1 is repeatedly failing to fire. The cause is almost always its coil, plug, injector… Moderate P0302 Powertrain Cylinder 2 keeps misfiring. On inline engines it's a middle cylinder, so rule out coolant… Moderate P0303 Powertrain Cylinder 3 is misfiring. Check whether it misses at idle or under load before you blame… Moderate P0304 Powertrain Cylinder 4 is misfiring. Its end or rear position makes water, oil and intake leaks common… Moderate P0325 Powertrain The computer isn't getting a usable signal from knock sensor 1, so it pulls timing to protect… Low

All codes (66)

All Severity 3+ Severity 4+
P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High P0301 Powertrain Cylinder 1 is repeatedly failing to fire. The cause is almost always its coil, plug, injector… Moderate P0302 Powertrain Cylinder 2 keeps misfiring. On inline engines it's a middle cylinder, so rule out coolant… Moderate P0303 Powertrain Cylinder 3 is misfiring. Check whether it misses at idle or under load before you blame… Moderate P0304 Powertrain Cylinder 4 is misfiring. Its end or rear position makes water, oil and intake leaks common… Moderate P0305 Powertrain Cylinder 5 is misfiring. First job: work out which bank it sits on, because that decides what… Moderate P0306 Powertrain Cylinder 6 is misfiring. On an inline-six it's the hot rear cylinder; on GM and Hemi V8s it can… Moderate P0307 Powertrain Cylinder 7 is misfiring. On GM and Hemi V8s it's a cylinder-deactivation cylinder, so check… Moderate P0308 Powertrain Cylinder 8 is misfiring. It's a rear V8 cylinder against the firewall, so its plug is often… Moderate P0316 Powertrain The engine misfired right after starting, when the catalytic converter is cold and emissions… Low P0320 Powertrain The computer lost the engine speed (rpm) signal. The engine can stall suddenly or refuse… High P0321 Powertrain The rpm signal is there but erratic: extra or missing pulses the computer can't trust. Expect… Moderate P0325 Powertrain The computer isn't getting a usable signal from knock sensor 1, so it pulls timing to protect… Low P0326 Powertrain Knock sensor 1 works electrically, but what it hears doesn't match what the computer expects. Low P0327 Powertrain Knock sensor 1's signal is too weak or pulled to ground: usually wiring, water or a loose… Low P0328 Powertrain Knock sensor 1's signal is too strong: a short to voltage, electrical noise or a genuinely… Low P0330 Powertrain The second knock sensor, usually the one for the bank without cylinder 1, has a circuit fault. Low P0332 Powertrain Knock sensor 2 reads too low. On a V engine it's the bank without cylinder 1; on some fours… Low P0335 Powertrain The engine computer lost the crankshaft position signal. Expect stalling or a crank-no-start. High P0336 Powertrain Crank signal present but implausible: damaged teeth, a slipped balancer ring or debris confuse… Moderate P0337 Powertrain The crank sensor signal line is stuck near 0 volts, usually a wire shorted to ground. Often… High P0338 Powertrain The crank signal line sits at 5 or 12 volts and stops switching: open ground, open wire… High P0339 Powertrain The crank signal drops out for moments at a time. Classic sign: stalls when hot, restarts once… High P0340 Powertrain The computer lost the camshaft signal on bank 1. Expect long cranking, less power… Moderate P0341 Powertrain The bank 1 cam signal lands at the wrong crank angle, often from a stretched chain or a sticky… Moderate P0342 Powertrain The bank 1 cam sensor signal stays near 0 volts. Often a weak battery, a pinched wire… Moderate P0343 Powertrain The bank 1 cam signal is stuck high: an unlatched connector, broken ground or open wire after… Moderate P0344 Powertrain The bank 1 cam sensor signal keeps dropping out for short moments, which can cause random… Moderate P0345 Powertrain The cam sensor on bank 2, the side without cylinder 1, has a missing or faulty signal on a V6… Moderate P0346 Powertrain Bank 2's cam signal arrives out of position. On V6/V8s that often means a bank 2 chain, guide… Moderate

Subsystems

Fuel & Air Metering 193Emission Controls 97Speed & Idle Control 57Transmission 57ECU & Outputs 54Module Communication 43Brakes, ABS & Chassis 36Body Systems 31Hybrid / EV 14