OBD2 Fault Code Library

Free lookup for thousands of OBD2 trouble codes: filter by family, read short meanings, and open deeper articles. Desktop ELM327 scanner with live data and AI guidance.

OBD2 symptoms

Look up diagnostic trouble codes by what the car is doing: misfire, overheating, rough idle, a check engine light, and other common symptoms.

U0404 — Invalid Data Received From Gear Shift Control Module (U0404): a vehicle network fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by internal mechanical wear (clutches, torque converter), faulty transmission speed sensor, failed shift or pressure control solenoid.
U0405 — U0405 — Invalid Data Received From Cruise Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: aftermarket equipment interfering with the bus, a faulty module pulling the bus down, poor grounds or low battery voltage.
U0407 — OBD2 code U0407 flags a problem with the diesel glow plug system (invalid data received from glow plug control module). The car is usually drivable while you plan the repair. Common culprits: faulty glow plug relay or control module, burned-out glow plug, blown fuse in the glow plug circuit.
U0408 — Invalid Data Received From Throttle Actuator Control Module (U0408): a vehicle network fault affecting the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Most often caused by dirty throttle body or stuck throttle plate, intake air leaks after the MAF sensor, faulty throttle position sensor or pedal sensor.
U0409 — OBD2 code U0409 flags a problem with the vehicle network (CAN bus) communication (invalid data received from alternative fuel control module). Short, gentle driving to a shop is usually possible. Common culprits: damaged CAN bus wiring or short to power/ground, a faulty module pulling the bus down, aftermarket equipment interfering with the bus.
U040A — OBD2 code U040A flags a problem with the vehicle network (CAN bus) communication (invalid data received from air conditioning control module). Short, gentle driving to a shop is usually possible. Common culprits: a faulty module pulling the bus down, damaged CAN bus wiring or short to power/ground, poor grounds or low battery voltage.
U040B — Invalid Data Received From Exhaust Gas Recirculation Control Module "A" (U040B): a vehicle network fault affecting the exhaust gas recirculation (EGR) system. The car is usually drivable while you plan the repair. Most often caused by vacuum leaks in EGR control lines, carbon buildup blocking the EGR valve or passages, failed EGR valve or position sensor.
U040C — Invalid Data Received From Exhaust Gas Recirculation Control Module "B" (U040C): a vehicle network fault affecting the exhaust gas recirculation (EGR) system. The car is usually drivable while you plan the repair. Most often caused by failed EGR valve or position sensor, ECM control circuit fault, vacuum leaks in EGR control lines.
U040D — OBD2 code U040D flags a problem with the turbocharger / supercharger boost control (invalid data received from turbocharger/supercharger control module "A"). Short, gentle driving to a shop is usually possible. Common culprits: faulty boost pressure sensor, clogged intake or exhaust (DPF/cat), worn turbocharger.
U040E — U040E — Invalid Data Received From Turbocharger/Supercharger Control Module "B". A fault in the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Typical causes: boost leak in intercooler piping or hoses, worn turbocharger, clogged intake or exhaust (DPF/cat).
U040F — OBD2 code U040F flags a problem with the vehicle network (CAN bus) communication (invalid data received from reductant control module). Short, gentle driving to a shop is usually possible. Common culprits: poor grounds or low battery voltage, aftermarket equipment interfering with the bus, damaged CAN bus wiring or short to power/ground.
U0415 — Invalid Data Received From Anti-Lock Brake System Control Module (U0415): a vehicle network fault affecting the ABS / stability control. Short, gentle driving to a shop is usually possible. Most often caused by blown fuse or low voltage to the ABS module, damaged sensor wiring or corroded connector, failed wheel speed sensor.
U0416 — Invalid Data Received From Vehicle Dynamics Control Module (U0416): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by aftermarket equipment interfering with the bus, corroded connectors, especially in wet areas, poor grounds or low battery voltage.
U0418 — Invalid Data Received From Brake System Control Module (U0418): a vehicle network fault affecting the ABS / stability control. Short, gentle driving to a shop is usually possible. Most often caused by failed wheel speed sensor, damaged sensor wiring or corroded connector, blown fuse or low voltage to the ABS module.
U0419 — U0419 — Invalid Data Received From Steering Effort Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: poor grounds or low battery voltage, a faulty module pulling the bus down, aftermarket equipment interfering with the bus.
U041B — U041B — Invalid Data Received From Exhaust Gas Sensor Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: a faulty module pulling the bus down, corroded connectors, especially in wet areas, poor grounds or low battery voltage.
U041C — U041C — Invalid Data Received From Rocker Arm Control Module "A". A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: aftermarket equipment interfering with the bus, a faulty module pulling the bus down, damaged CAN bus wiring or short to power/ground.
U041D — U041D — Invalid Data Received From Rocker Arm Control Module "B". A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: poor grounds or low battery voltage, water ingress in harness junctions, aftermarket equipment interfering with the bus.
U041E — Invalid Data Received From All Wheel Drive Control Module (U041E): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by damaged CAN bus wiring or short to power/ground, corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus.
U0421 — U0421 — Invalid Data Received From Ride Level Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.
U0422 — OBD2 code U0422 flags a problem with the vehicle network (CAN bus) communication (invalid data received from body control module). Short, gentle driving to a shop is usually possible. Common culprits: corroded connectors, especially in wet areas, damaged CAN bus wiring or short to power/ground, water ingress in harness junctions.
U0424 — U0424 — Invalid Data Received From HVAC Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: a faulty module pulling the bus down, corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus.
U0425 — U0425 — Invalid Data Received From Auxiliary Heater Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: water ingress in harness junctions, aftermarket equipment interfering with the bus, poor grounds or low battery voltage.
U0426 — OBD2 code U0426 flags a problem with the vehicle network (CAN bus) communication (invalid data received from vehicle immobilizer control module). Short, gentle driving to a shop is usually possible. Common culprits: damaged CAN bus wiring or short to power/ground, water ingress in harness junctions, poor grounds or low battery voltage.