Systematic Troubleshooting

General Information

The ignition must always be switched off when removing and installing electronic control units or disconnecting and connecting the connectors of the control units.

When components, relays, fuses etc. are removed and installed, defect codes may be stored in the defect code memories of control units capable of diagnostic procedures. For this reason, the defect code must always be monitored after working on the electrical system (*D* Quick test). Examine stored defect codes and delete (*D* Clear defect code memory).

The defect code memories of the majority of control units are cleared by disconnecting the power supply. Therefore, before disconnecting the vehicle battery monitor the relevant memory (*D* Quick test or select the corresponding control unit) and examine stored defect codes.

Before starting the troubleshooting procedure, stored defect codes should always be printed out on the printer of the BMW SERVICE TESTER.

Testing Equipment and Aids

Adapters

A comprehensive system of adapters is available for conducting tests on the plug-and-socket connections. All tests should always be performed using the matching adapters.

If no special adapter is available to perform a test, appropriate aids (test leads, terminals probe tips) must be used as a substitute.

Measuring instruments

All the described measurements can be performed with the BMW SERVICE TESTER. In addition, measuring instruments (multimeter) approved by BMW can also be used.

Fused jumper wire

When a bypass at a wire harness is specified in the diagnostic procedure, only a fused jumper wire must be used for this purpose.

A fused jumper wire is made up of a fuse holder connected to a set of test leads. The fuse should be selected such that no damage can occur in the vehicle in the case of fault.