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

P0630 Powertrain The engine computer has no VIN stored, or one that doesn't match the car – a classic after… Low P0638 Powertrain The electronic throttle or diesel intake throttle can't reach its commanded angle, often due… Moderate P0641 Powertrain The PCM's shared 5-volt supply 'A' is missing or out of range – often one shorted sensor… High P0642 Powertrain The PCM's 5-volt supply 'A' is being pulled below spec, usually by a short to ground in one… High P0651 Powertrain The PCM's second 5-volt sensor supply is out of range – usually a pedal, throttle or pressure… Moderate P0670 Powertrain The engine computer can't properly control or hear back from the diesel's glow plug control… Low P0671 Powertrain The glow plug in cylinder 1 or its wire isn't drawing normal current. Usually the plug itself… Low P0685 Powertrain The engine computer can't switch its own main power relay – open coil, blown fuse or broken… High P0686 Powertrain The main relay control line is being pulled to ground – usually a shorted relay coil… Moderate P0687 Powertrain The main relay control line sits at battery voltage – the relay may never switch on or never… Moderate P0690 Powertrain The ECM still sees power coming through its main relay when the relay should be off – often… Low P069E Chevrolet · Powertrain The fuel pump control module stored its own fault and asked the engine computer for the check… Moderate P06DD Powertrain The ECM commanded an oil pressure change and the measured pressure didn't respond – check… High P0700 Powertrain The transmission computer found a fault and asked for the check engine light – read the TCM… Moderate P0705 Powertrain The computer can't make sense of the gear selector position signal – P, R, N, D may be misread. Moderate P0706 Powertrain The range sensor works electrically, but its reading doesn't match where the lever and gears… Moderate P0707 Powertrain The range sensor signal voltage is below its lowest valid value – usually a short to ground… Moderate P0710 Powertrain The transmission computer lost a usable fluid temperature signal and is guessing… Low P0711 Powertrain The fluid temperature reading doesn't behave like real fluid – it warms too slowly, too fast… Moderate P0712 Powertrain The fluid temperature signal voltage is too low, so the computer thinks the fluid is extremely… Moderate P0715 Powertrain The transmission computer has lost a reliable input-shaft speed signal, so shifts get harsh… Moderate P0716 Powertrain The input speed signal is there but erratic or illogical – dropouts, spikes or values that… Moderate P0717 Powertrain The input speed sensor reports zero while the engine runs and the car moves – the signal… Moderate P0720 Powertrain Electrical fault in the output shaft speed signal – shift timing and sometimes the speedometer… Moderate P0721 Powertrain The output speed signal is noisy, drops out or doesn't agree with wheel speed or input speed. Low P0722 Powertrain The output speed sensor sends nothing while the car moves – shifting and often the speedometer… Moderate P0730 Powertrain The transmission computer sees input and output shaft speeds that don't fit the gear it… High P0731 Powertrain While in first gear, the transmission's input and output speeds don't match the first-gear… Moderate P0732 Powertrain Second gear isn't holding: the input-to-output speed ratio in 2nd is outside the expected range. Moderate P0733 Powertrain Third gear slips: input shaft speed doesn't match output speed times the 3rd-gear ratio. Moderate