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.

• Engine misfire
• Engine overheating
• Rough idle
• Check engine light
• Poor fuel economy
• Hard starting
• Engine stalling
• Catalytic converter efficiency
• Oxygen sensor fault
• EVAP leak
• Thermostat not reaching temperature
• Lean air-fuel mixture
• Rich air-fuel mixture
• EGR flow fault
• Engine knock
• Charging system
• Throttle position
• Mass airflow sensor
• Turbo underboost
• Coolant temperature sensor
• Transmission fault

• U1023 — U1023 — SCP (J1850) Invalid or Missing Data for Primary Id. 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, corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus.
• U1024 — OBD2 code U1024 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for primary id). 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.
• U1025 — OBD2 code U1025 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for primary id). Short, gentle driving to a shop is usually possible. Common culprits: aftermarket equipment interfering with the bus, damaged CAN bus wiring or short to power/ground, poor grounds or low battery voltage.
• U1026 — U1026 — SCP (J1850) Invalid or Missing Data for Engine RPM. 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.
• U1027 — OBD2 code U1027 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for engine RPM). Short, gentle driving to a shop is usually possible. Common culprits: a faulty module pulling the bus down, aftermarket equipment interfering with the bus, corroded connectors, especially in wet areas.
• U1028 — SCP (J1850) Invalid or Missing Data for Primary Id (U1028): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by water ingress in harness junctions, a faulty module pulling the bus down, aftermarket equipment interfering with the bus.
• U1029 — U1029 — SCP (J1850) Invalid or Missing Data for Primary Id. 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, poor grounds or low battery voltage.
• U1030 — U1030 — SCP (J1850) Invalid or Missing Data for Experimental #1. 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, water ingress in harness junctions, poor grounds or low battery voltage.
• U1031 — OBD2 code U1031 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for experimental #1). Short, gentle driving to a shop is usually possible. Common culprits: poor grounds or low battery voltage, aftermarket equipment interfering with the bus, water ingress in harness junctions.
• U1032 — U1032 — SCP (J1850) Invalid or Missing Data for Primary Id. 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.
• U1033 — OBD2 code U1033 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for primary id). Short, gentle driving to a shop is usually possible. Common culprits: poor grounds or low battery voltage, a faulty module pulling the bus down, water ingress in harness junctions.
• U1034 — OBD2 code U1034 flags a problem with the vehicle network (CAN bus) communication (SCP (J1850) invalid or missing data for primary id). 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, water ingress in harness junctions.
• U1035 — SCP (J1850) Invalid or Missing Data for Primary Id (U1035): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by poor grounds or low battery voltage, aftermarket equipment interfering with the bus, water ingress in harness junctions.
• U1036 — U1036 — SCP (J1850) Invalid or Missing Data for Wheels. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: damaged CAN bus wiring or short to power/ground, corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus.
• U1037 — SCP (J1850) Invalid or Missing Data for Wheels (U1037): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by poor grounds or low battery voltage, aftermarket equipment interfering with the bus, damaged CAN bus wiring or short to power/ground.
• U1038 — SCP (J1850) Invalid or Missing Data for Primary Id (U1038): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by poor grounds or low battery voltage, aftermarket equipment interfering with the bus, water ingress in harness junctions.
• U1039 — SCP (J1850) Invalid or Missing Data for Primary Id / Vehicle Speed (U1039): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by corroded connectors, especially in wet areas, water ingress in harness junctions, damaged CAN bus wiring or short to power/ground.
• U1040 — SCP (J1850) Invalid or Missing Data for Vehicle Speed (U1040): 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, a faulty module pulling the bus down, aftermarket equipment interfering with the bus.
• U1042 — OBD2 code U1042 flags a problem with the ABS / stability control (SCP (J1850) invalid or missing data for traction control). Short, gentle driving to a shop is usually possible. Common culprits: faulty ABS module or pump motor, blown fuse or low voltage to the ABS module, damaged sensor wiring or corroded connector.
• U1043 — U1043 — SCP (J1850) Invalid or Missing Data for Traction Control. A fault in the ABS / stability control. Short, gentle driving to a shop is usually possible. Typical causes: damaged tone (reluctor) ring on the hub, damaged sensor wiring or corroded connector, blown fuse or low voltage to the ABS module.
• U1044 — SCP (J1850) Invalid or Missing Data for Traction Motor (U1044): a vehicle network fault affecting the ABS / stability control. Short, gentle driving to a shop is usually possible. Most often caused by faulty ABS module or pump motor, damaged sensor wiring or corroded connector, blown fuse or low voltage to the ABS module.
• U1045 — SCP (J1850) Invalid or Missing Data for Traction Motor (U1045): a vehicle network fault affecting the ABS / stability control. Short, gentle driving to a shop is usually possible. Most often caused by damaged sensor wiring or corroded connector, blown fuse or low voltage to the ABS module, failed wheel speed sensor.
• U1046 — U1046 — SCP (J1850) Invalid or Missing Data for Primary Id. 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, damaged CAN bus wiring or short to power/ground, a faulty module pulling the bus down.
• U1047 — U1047 — SCP (J1850) Invalid or Missing Data for Primary Id. 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, damaged CAN bus wiring or short to power/ground, aftermarket equipment interfering with the bus.