Understand your check engine light.
Plain-language answers for every diagnostic code, specific to your exact vehicle.
Look up a code
400+ OBD-II codes explained: causes, severity, and how to fix it.
Browse codes →Decode your VIN
Open recalls, service bulletins, and full specs in seconds. Free.
Check my VIN →Everything for your vehicle
Fluid capacities, common problems, open recalls, and maintenance specs, by year, make, and model.
Find my vehicle →Warranty Guide
Every brand’s factory coverage compared, by a former warranty administrator who processed the claims.
Compare brands →Owner’s Manual Finder
Your manual is free; we link you straight to the official manufacturer download for every make.
Find my manual →No code? Start with the symptom
Shaking, squealing, smoking, won’t start: causes ranked by likelihood and cost, cheapest checks first.
Browse symptoms →Most-looked-up codes
Browse all codes →Jump straight to the trouble codes drivers search for most: what each means, the likely causes, and how to fix it without throwing parts at the problem.
- P0300 Random/Multiple Cylinder Misfire Detected
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)
- P0301 Cylinder 1 Misfire Detected
- P0171 System Too Lean (Bank 1)
- P0128 Coolant Thermostat: Temperature Below Regulating Temperature
- P0455 EVAP Large Leak Detected
- P0442 EVAP Small Leak Detected
- P0101 Mass Air Flow (MAF) Sensor: Circuit Range/Performance
- P0700 Transmission Control System Malfunction
- P0174 System Too Lean (Bank 2)
- P0430 Catalyst System Efficiency Below Threshold (Bank 2)
- P0340 Camshaft Position (CMP) Sensor: Circuit Malfunction
