When Replacing Electronic Control Units

CAUTION:
- Disconnecting the car's battery will cancel the fault memories of control units.
- Consequently prior to disconnection of the car's battery fault memories should be interrogated and faults printed by the printer of a BMW Service Tester. Investigate stored faults.
- Ignition must always be switched off before disconnecting or connecting control unit plugs.
- Removal and installation of components, relays, fuses etc. could cause the storage of faults in fault memories of control units capable of self-diagnosis.
- Consequently fault memories must always be interrogated alter working on the electrical system. Stored faults must be investigated and cancelled.

NOTE: When Replacing DME (Digital Motor Electronics) Control Unit:
- Each control unit is programed with certain basic values, which serve as mean values.
- The control unit receives different input values, depending on engine condition, which are compared with the stored values.
- The adaptive system compares the input values with the stored map values. appropriate correction commands are sent to the concerned drive elements.
- If, for example, the DME control unit would be without current for a long time (more than an hour), its adaptive system would lose the stored values.
- After re-operation of a cancelled or installation of a new control unit the input values of a pertinent engine must be read in and stored for the adaptive system. This procedure could lead to erratic idling and disturbed overrunning of the engine after starting. Depending on the engine it could require some time before all values are adapted to the engine condition.
- Consequently there must be conformance with the following procedures before replacing a DME control unit or operating a control unit which had been disconnected.
- Run engine to operating temperature.
- Install control unit and drive car.