OBD-II Diagnostic Trouble Codes
Enter the code from your diagnostic scanner (e.g. P0301) and see what it means — in plain language, with severity, symptoms, causes and recommended action.
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How to read a code — for example P0301
- P — system: P = powertrain, C = chassis, B = body, U = network.
- 0 — 0 = generic (standardized) code; 1 = manufacturer-specific.
- 3 — subsystem (here: ignition / misfire).
- 01 — the specific fault (here: cylinder 1).
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All codes by system
P — Powertrain (engine & transmission) (35)
C — Chassis (ABS, brakes, steering) (1)
B — Body (airbags, A/C, lighting) (1)
U — Network & communication (CAN bus) (2)
Frequently asked questions
What is an OBD-II trouble code?
An OBD-II (on-board diagnostics) code is a standardized fault code your car's computer stores when it detects a problem. It is read with a diagnostic scanner via the OBD-II port (usually under the dashboard).
How do I read a code like P0301?
The first letter is the system (P = powertrain, C = chassis, B = body, U = network). The first digit shows whether the code is generic (0) or manufacturer-specific (1). The remaining digits identify the subsystem and the specific fault.
My check-engine light is on — is it safe to drive?
A steady light usually means you can drive carefully to a workshop. A flashing light signals a severe misfire — stop, as it can damage the catalytic converter.
Can I clear the code myself?
A scanner can clear a code, but if the underlying fault is not fixed it will return. Clearing also resets the readiness monitors needed for an emissions test.
Are these explanations accurate for my car?
Generic codes are standardized across all makes, but exact causes and procedures vary. This is general reference information, not a substitute for a workshop diagnosis.
Where does this data come from?
The code structure follows the SAE J2012 standard, and explanations are based on common automotive references. Everything runs in your browser, with no tracking.
This is general reference information based on the SAE J2012 standard. Exact causes and procedures for your vehicle may differ — when in doubt, consult a workshop.