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

P0457 Powertrain The EVAP leak test found the system wide open — almost always a loose, missing or worn gas cap. Minor P0458 Powertrain The purge valve control line reads too low: lost power feed, open coil or a wire shorted… Low P0459 Powertrain The purge valve control line stays high when the ECU grounds it: a short to power or a shorted… Low P0460 Powertrain The engine computer gets no usable fuel level signal – often a tank-top connector or the sender… Low P0461 Powertrain The fuel level reading doesn't change the way fuel use says it should – usually a worn or stuck… Low P0462 Powertrain Fuel level signal voltage stuck near zero – usually a shorted sender or a signal wire rubbing… Low P0463 Powertrain Fuel level signal reads like an open circuit – most often a corroded tank-top connector… Low P0471 Powertrain The exhaust backpressure reading doesn't match what the computer expects; the sensor tube… Moderate P0472 Powertrain Exhaust backpressure sensor signal near zero volts: dead sensor, grounded wire or lost 5 V… Moderate P0480 Powertrain Fault in the circuit that switches the main radiator fan – the engine can overheat in traffic. Moderate P0481 Powertrain The second fan output – a second fan or the high-speed stage – has a circuit fault; A/C suffers… Low P0491 Powertrain Too little cold-start air reached the bank 1 exhaust during the self-test; pump, combi valve… Low P0492 Powertrain The cold-start air check found too little air on the bank 2 side only, so look at that side's… Low P0496 Powertrain Vapor is being drawn into the engine while purge is commanded off: almost always a purge valve… Low P0497 Powertrain Purge is commanded but too little vapor reaches the engine: blockage, closed valve or weak… Minor P0500 Powertrain The engine computer lost its vehicle speed signal – speedometer, shifting and cruise control… Moderate P0501 Powertrain A speed signal exists, but it doesn't match what engine rpm, gear and other sensors say the car… Low P0503 Powertrain The speed signal jumps, spikes or reads impossibly high – usually electrical noise or a loose… Low P0504 Powertrain The two contacts in the brake pedal switch disagree on whether you're braking; check the pedal… Moderate P0505 Powertrain The engine computer can't hold idle speed where it wants it – usually a dirty or sticking idle… Low P0506 Powertrain The engine idles below the computer's target even with idle air opened up – usually a gummed-up… Low P0507 Powertrain The engine idles faster than the computer's target – most often extra air is sneaking… Low P0508 Powertrain The idle air control circuit reads low voltage – a shorted valve coil, lost power feed or wire… Low P0509 Powertrain The ECU sees too much voltage on the idle air valve circuit, so it has lost control of the idle… Low P0511 Powertrain The computer can't drive the idle air control valve properly – typically an open winding… Low P0520 Powertrain The engine computer gets a signal from the oil pressure sensor or switch that makes no… Moderate P0521 Powertrain The oil pressure reading doesn't fit engine speed and temperature – a drifting sensor or truly… High P0522 Powertrain The oil pressure signal is below what a working sensor can produce – usually wiring… Moderate P0523 Powertrain The oil pressure signal is stuck near 5 volts, above any real pressure – almost always sensor… Low P0524 Powertrain Measured oil pressure fell below the safe minimum. Stop the engine now and check the oil before… Critical