Trouble code directory
Every generic OBD-II code — 9,533 of them — is searchable here. Type the code from your scanner, or browse the catalogue by system below.
- P0420Catalyst System Efficiency Below Threshold (Bank 1)Severity level 3 of 5: Diagnose soon.
- P0171System Too Lean (Bank 1)Severity level 3 of 5: Diagnose soon.
- P0300Random/Multiple Cylinder Misfire DetectedSeverity level 4 of 5: Get it looked at now.
- P0430Catalyst System Efficiency Below Threshold (Bank 2)Severity level 3 of 5: Diagnose soon.
- P0455Evaporative Emission System Leak Detected (Large Leak)Severity level 2 of 5: Not urgent.
- P0128Coolant Thermostat Below Regulating TemperatureSeverity level 2 of 5: Not urgent.
- P0442Evaporative Emission System Leak Detected (Small Leak)Severity level 2 of 5: Not urgent.
- P0301Cylinder 1 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
- P0172System Too Rich (Bank 1)Severity level 3 of 5: Diagnose soon.
- P0011"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)Severity level 3 of 5: Diagnose soon.
- P0016Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)Severity level 4 of 5: Get it looked at now.
- P0174System Too Lean (Bank 2)Severity level 3 of 5: Diagnose soon.
- P0302Cylinder 2 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
- P0303Cylinder 3 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
- P0304Cylinder 4 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
- P0401Exhaust Gas Recirculation Flow Insufficient DetectedSeverity level 3 of 5: Diagnose soon.
Engine, transmission, fuel, ignition and emissions control.
Module-to-module communication across the vehicle data bus.
Braking, steering, suspension and stability control.
Interior and comfort systems, lighting, restraints and climate control.
These are the generic codes — the set every OBD-II scan tool understands, defined by SAE J2012 and ISO 15031-6. A code beginning P0, B0,C0 or U0 means the same thing on a Ford as it does on a Honda.
Codes beginning P1 and similar are defined by the vehicle manufacturer, and the same code number means different things on different makes. We do not publish generic definitions for those, because there is no correct generic definition to publish.
We publish deep diagnostic guidance only for codes that have been through editorial review. The rest are searchable and carry their standard definition and structured relationships.How we decide what to publish →