Check engine light on: Codes, Causes & Fixes

P0174 Powertrain The cylinder bank without cylinder 1 is running lean even with the maximum fuel correction… Moderate P0420 Powertrain The bank 1 catalytic converter no longer stores enough oxygen to clean the exhaust properly. Low P0101 Powertrain The MAF sensor's airflow reading doesn't match what the engine computer expects… Low P0113 Powertrain The intake air temperature signal is stuck at maximum voltage, which usually means an open… Low P0135 Powertrain The heater inside the upstream oxygen sensor on bank 1 isn't working or its circuit is faulty. Low P0171 Powertrain The engine computer is adding the maximum extra fuel it's allowed on bank 1 and still sees… Moderate

P0232 Powertrain The fuel pump feed wire has voltage on it when the engine computer has switched the pump off. Moderate P0234 Powertrain Boost rose above the safe limit the engine computer allows, so it may cut power to protect… High P0235 Powertrain The engine computer found an electrical fault in the boost pressure sensor's wiring… Moderate P0236 Powertrain The boost sensor's signal is electrically OK, but its readings don't make sense compared… Moderate P0237 Powertrain The boost sensor signal has dropped near zero volts, reading less pressure than the atmosphere… Moderate P0238 Powertrain The boost sensor signal is stuck near 5 volts, so the computer sees impossibly high boost… Moderate P0243 Powertrain The engine computer found a fault in the electrical circuit of the solenoid that controls… Moderate P0246 Powertrain The wastegate solenoid control circuit reads too high, usually a short to power or a shorted… Low P0263 Powertrain Cylinder 1 is producing noticeably more or less power than the others, beyond what fuel trim… Moderate P0266 Powertrain The engine computer can't even out cylinder 2 with fuel corrections; its balance rate is past… Moderate P0269 Powertrain Cylinder 3 isn't pulling its weight, or is pulling too hard, and the fuel correction for it… Moderate P0272 Powertrain The ECU can't balance cylinder 4 against the rest anymore; its fuel correction is outside… Moderate P0275 Powertrain The fuel correction for cylinder 5 is past its limit. Only engines with five or more cylinders… Moderate P0299 Powertrain The turbo or supercharger isn't building the boost pressure the engine computer is asking for. Moderate 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