Tool
OBD2 code decoder
Every OBD2 code follows the same five-character pattern. Type one in and the decoder explains each part.
Short answer
The letter names the system (P powertrain, B body, C chassis, U network). The first digit says whether the code is generic (0) or set by the maker (1). For P codes the second digit names the subsystem, and the last two identify the exact fault.
Decode a code
How a trouble code is built
OBD2 trouble codes follow the SAE J2012 standard, so the structure is the same on every car and light truck sold in the US since 1996. The letter and the first digit tell you where the fault is and who defined the code. The rest narrows it down to one test that failed.
P powertrain, B body, C chassis, U network
0 generic (same on every car), 1 set by the maker
For P codes: 4 means auxiliary emission controls
The exact fault: here, catalyst efficiency, bank 1
The letter: which system
| Letter | System | Typical lamp |
|---|---|---|
| P | Powertrain: engine, transmission, fuel and emissions | Check engine |
| B | Body: airbags, seat belts, climate, lighting | Airbag (SRS) or none |
| C | Chassis: ABS, traction and stability control, steering | ABS or traction control |
| U | Network: communication between modules | Varies, often several |
The third character of a P code
| Digit | Subsystem |
|---|---|
| 1, 2 | Fuel and air metering |
| 3 | Ignition system or misfire |
| 4 | Auxiliary emission controls (EGR, EVAP, catalyst) |
| 5 | Vehicle speed, idle control and auxiliary inputs |
| 6 | Computer and output circuits |
| 7, 8, 9 | Transmission |
A code tells you which self-test failed, not which part is broken. Read the freeze frame and live data before buying parts, and look for other codes that could have caused this one. Engine codes are covered in engine and emissions codes; ABS, airbag and network codes in ABS, airbag and network codes.