How to read a BMW fault code

Thanks to the OBD system, BMWs manufactured after 1996 are typically equipped with an OBD diagnostic port. If the car’s computer encounters a problem, an error code or diagnostic trouble code (DTC) will be stored in the car’s ECU memory. With an OBD reader (K+DCAN or ENET) plugged into the car’s OBD (On-Board Diagnostics) port and a dedicated diagnostics software (ISTA for BMW), you can read the list of stored codes and thus discover what the problem is.

The first letter

The first letter indicates which part of the car is at fault:

P = Powertrain (Engine and Transmission)

B = Body

C = Chassis

U = User (Communication Network)

The second digit

The second digit indicates which of the car’s systems is at fault. There are eight different categories:

0 : Fuel and Air Measurement and Auxiliary Emission Control

1 : Fuel and Air Measurement

2 : Fuel and Air Metering (Fuel Injection Circuit)

3 : Ignition Systems or Misfires

4 : Auxiliary Emission Controls

5 : Vehicle Speed Control and Idle Control Systems

6 : Computer and Output Circuit

7 : Transmission

The third and fourth digits

The third and fourth digits are simply used to define the exact fault code in question. There are also many manufacturer-specific codes that do not follow the SAE standard.

The codes follow a formula that generally allows you to know what the problem is.