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

P2463 Powertrain The DPF is loaded with more soot than the ECU allows; it needs a regen or cleaning before it… High P246C Powertrain The DPF is so restricted that the ECM has cut engine power to protect the turbo, EGR system… High P2502 Powertrain The ECM distrusts the charging system – no output, wrong voltage or an implausible alternator… Moderate P2503 Powertrain The alternator can't reach the voltage the ECM asks for – usually a worn alternator or slipping… Moderate P2504 Powertrain The charging system is overcharging – too much voltage can boil the battery and damage… High P25A2 Chevrolet · Powertrain The brake module stored a fault and asked the engine computer to turn on the check engine light. Moderate P2646 Powertrain The engine asked VTEC to switch to the high-lift cam, but the oil pressure switch never saw… Low P2647 Powertrain The VTEC oil pressure switch reports the high-lift rockers engaged while the engine computer… Moderate P26B7 Ford · Powertrain The PCM sees an open circuit to the electric coolant bypass valve on Ford's 1.6L EcoBoost… Moderate P2714 Powertrain Transmission pressure solenoid D isn't regulating pressure as commanded – a classic source… Moderate P2716 Powertrain The transmission computer sees an open or short in the circuit of pressure control solenoid D. Moderate P2BAC Powertrain EGR has been shut off because of a fault, so NOx is above the limit; fix the EGR code stored… Moderate P3000 Toyota · Powertrain Toyota's hybrid computer flags a fault in the high-voltage battery system and limits hybrid… High P3081 Volkswagen · Powertrain The engine didn't warm up as fast as the ECU expected – most often a thermostat stuck open. Low P3190 Toyota · Powertrain The hybrid computer asked the gas engine for power and got less than expected. Moderate P3191 Toyota · Powertrain The hybrid system spun the gas engine with its motor-generator, but the engine never fired up. High P3400 Powertrain Cylinder shut-off on bank 1 (AFM, DFM, MDS or VCM) isn't doing what the engine computer… Moderate P3401 Powertrain The engine computer sees a broken or open circuit to the solenoid that shuts off cylinder 1. Low P3497 Honda · Powertrain Honda's Variable Cylinder Management on the front cylinder bank didn't behave the way the PCM… Moderate U0001 Network A module found the high-speed CAN network itself misbehaving, not just one silent module. High U0073 Network A module saw so many errors on CAN bus A that it shut off its own transmitter. High U0100 Network Another module stopped hearing from the engine computer on the CAN network. High U0101 Network The engine computer and other modules stopped hearing from the transmission control module. High U0102 Network Other modules can't hear the 4WD transfer case module, so 4WD shifting is disabled. Moderate U0104 Network The adaptive cruise radar (or cruise module) went silent on the network, so cruise is switched… Low U0105 Network The PCM lost contact with the separate module that fires the injectors, common on diesel… High U0107 Network The engine computer can't reach the module that drives the electronic throttle, so power is cut… High U0109 Network The PCM lost contact with the module that controls fuel pump speed; stalling or no-start can… High U0110 Network The hybrid/EV system lost contact with the module that runs electric drive motor A. Critical U0114 Network The module that engages the AWD coupling went silent; the car falls back to front… Low