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GM fault codes

402 GM OBD-II fault codes: what each one means, and how to track it down.

How to read a code

P
SystemPowertrain
0
Defined bySAE, the same on every car
4
AreaAuxiliary emission controls
20
FaultThe specific fault in that area

  1. Read the code

    Note every stored and pending code your scanner shows, such as P0420.

  2. Find it

    Search by code or by words. For a manufacturer code (P1, B1, C1, U1) pick your make: its meaning differs by make.

  3. Open the code

    Its page explains the symptoms, likely causes, the checks to run and the fixes.