Code or symptom/
OBD-II trouble code lookup

Understand what your car is telling you.

Your car stored a code because a control module measured something outside its expected range. Type it in and we will tell you what it detected, how serious it is, and what to test before you replace anything.

CommonP0420P0171P0300P0430P0455No code? Start with what you noticed

Anatomy of a trouble code
PSystemPowertrainP, B, C or U
0Code typeGeneric (SAE)0 = standard, 1 = manufacturer
4SubsystemEmissions & auxiliarywhich area of the system
20Fault indexSpecific faultthe exact condition detected

Read left to right, a code tells you which system reported the fault, whether the definition is standardised or specific to your manufacturer, which part of that system is involved, and what exactly was detected. It does not tell you which part has failed.

Browse 9,533 generic codes by system
PrefixSystemWhat it coversCodes
PxxxxPowertrainEngine, transmission, fuel, ignition and emissions control7,355
UxxxxNetwork & communicationModule-to-module communication across the vehicle data bus1,229
CxxxxChassisBraking, steering, suspension and stability control626
BxxxxBodyLighting, climate control, restraints and cabin equipment323

Manufacturer-specific codes (P1xxx and similar) mean different things on different vehicles. We do not publish generic definitions for them, because there is no such thing as a correct generic definition for a code the manufacturer defines.

Most looked up
  1. P0420Catalyst System Efficiency Below Threshold (Bank 1)Severity level 3 of 5: Diagnose soon.
  2. P0171System Too Lean (Bank 1)Severity level 3 of 5: Diagnose soon.
  3. P0300Random/Multiple Cylinder Misfire DetectedSeverity level 4 of 5: Get it looked at now.
  4. P0430Catalyst System Efficiency Below Threshold (Bank 2)Severity level 3 of 5: Diagnose soon.
  5. P0455Evaporative Emission System Leak Detected (Large Leak)Severity level 2 of 5: Not urgent.
  6. P0128Coolant Thermostat Below Regulating TemperatureSeverity level 2 of 5: Not urgent.
  7. P0442Evaporative Emission System Leak Detected (Small Leak)Severity level 2 of 5: Not urgent.
  8. P0301Cylinder 1 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
  9. P0172System Too Rich (Bank 1)Severity level 3 of 5: Diagnose soon.
  10. P0011"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)Severity level 3 of 5: Diagnose soon.
  11. P0016Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)Severity level 4 of 5: Get it looked at now.
  12. P0174System Too Lean (Bank 2)Severity level 3 of 5: Diagnose soon.
  13. P0302Cylinder 2 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
  14. P0303Cylinder 3 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
  15. P0304Cylinder 4 Misfire DetectedSeverity level 4 of 5: Get it looked at now.
  16. P0401Exhaust Gas Recirculation Flow Insufficient DetectedSeverity level 3 of 5: Diagnose soon.
No code? Start with what you noticed

Definitions from an open, public-domain database of the SAE J2012 / ISO 15031-6 generic code set. Recall and vehicle data from NHTSA.Diagnostic guidance written and reviewed in-house — we do not claim certifications we do not hold. How this site works ·Data sources