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.

U3008 — Control Module Ground "A" (U3008): a vehicle network fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by a faulty module pulling the bus down, damaged CAN bus wiring or short to power/ground, water ingress in harness junctions.
U3009 — Control Module Ground "B" (U3009): 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, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.
U300A — U300A — Ignition Switch. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM, damaged coil wiring or connector.
U300B — Ignition Input Accessory/On/Start (U300B): a vehicle network fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by faulty ignition control circuit in the ECM, moisture or oil in the spark plug wells, failed ignition coil or coil pack.
U300C — Ignition Input Off/On/Start (U300C): a vehicle network fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by worn spark plugs or wrong plug gap, damaged coil wiring or connector, faulty ignition control circuit in the ECM.
U300D — U300D — Ignition Input On/Start. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: worn spark plugs or wrong plug gap, failed ignition coil or coil pack, moisture or oil in the spark plug wells.
U300F — OBD2 code U300F flags a problem with the ignition system (ignition input accessory). Short, gentle driving to a shop is usually possible. Common culprits: moisture or oil in the spark plug wells, failed ignition coil or coil pack, worn spark plugs or wrong plug gap.
U3010 — Ignition Input Start (U3010): a vehicle network fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by failed ignition coil or coil pack, moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM.
U3011 — OBD2 code U3011 flags a problem with the ignition system (ignition input off). Short, gentle driving to a shop is usually possible. Common culprits: faulty ignition control circuit in the ECM, worn spark plugs or wrong plug gap, moisture or oil in the spark plug wells.
U3012 — U3012 — U3012 - Control Module Input Power A Circuit Range. 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, poor grounds or low battery voltage.
U3014 — OBD2 code U3014 flags a problem with the vehicle network (CAN bus) communication (U3014 - control module input power b circuit low). Short, gentle driving to a shop is usually possible. Common culprits: aftermarket equipment interfering with the bus, corroded connectors, especially in wet areas, damaged CAN bus wiring or short to power/ground.
U3015 — OBD2 code U3015 flags a problem with the vehicle network (CAN bus) communication (U3015 - control module input power b circuit high). Short, gentle driving to a shop is usually possible. Common culprits: damaged CAN bus wiring or short to power/ground, poor grounds or low battery voltage, water ingress in harness junctions.
U3016 — OBD2 code U3016 flags a problem with the vehicle network (CAN bus) communication (U3016 - control module input power b circuit open). Short, gentle driving to a shop is usually possible. Common culprits: damaged CAN bus wiring or short to power/ground, corroded connectors, especially in wet areas, a faulty module pulling the bus down.
U3017 — U3017 - Control Module Input Power B Circuit Intermittent (U3017): a vehicle 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, corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus.
U3018 — U3018 - Control Module Input Power B Circuit Performance (U3018): a vehicle 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, poor grounds or low battery voltage, damaged CAN bus wiring or short to power/ground.
U3019 — U3019 - Control Module Input Power B Circuit Range (U3019): a vehicle 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, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.
U3020 — U3020 - Control Module Input Power C Circuit (U3020): a vehicle fault affecting the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Most often caused by a faulty module pulling the bus down, poor grounds or low battery voltage, corroded connectors, especially in wet areas.
U3021 — U3021 — U3021 - Control Module Input Power C Circuit Low. 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, damaged CAN bus wiring or short to power/ground, a faulty module pulling the bus down.
U3022 — U3022 - Control Module Input Power C Circuit High (U3022): a vehicle 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, damaged CAN bus wiring or short to power/ground, poor grounds or low battery voltage.
U3023 — U3023 — U3023 - Control Module Input Power C Circuit Open. 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, corroded connectors, especially in wet areas, water ingress in harness junctions.
U3024 — U3024 — U3024 - Control Module Input Power C Circuit Intermittent. 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, poor grounds or low battery voltage, a faulty module pulling the bus down.
U3025 — U3025 — U3025 - Control Module Input Power C Circuit Performance. 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.
U3026 — U3026 — U3026 - Control Module Input Power C Circuit Range. 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, poor grounds or low battery voltage, damaged CAN bus wiring or short to power/ground.
U3027 — U3027 - Control Module Input Power D Circuit (U3027): a vehicle 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, water ingress in harness junctions, poor grounds or low battery voltage.