Computers and Control Systems: Service and Repair

12 00 ... Instructions for removal and replacement of control units

IMPORTANT:
- Disconnecting the vehicle battery will cancel the fault memories of control units. Consequently, before disconnecting the car's battery, always interrogate the fault memories. Investigate stored faults and, once any faults have been remedied, cancel the fault memory.
- Control unit plugs should only ever be connected and disconnected while the ignition is turned off.
- The removal and installation of components, relays, fuses etc. can cause faults to be stored in fault memories capable of self diagnosis. Always interrogate the fault memories after completing work on the electrical system.
- Investigate stored faults and, once any faults have been remedied, cancel the fault memory.
- If necessary, initialise power window regulator Initialise power window regulator

On replacement of the DME/DDE control unit note the following:
- In every case use the diagnosis system to read out the hardware/software version of the corresponding control unit.

Comply with the diagnosis system instructions for the encoding and programming work operations.

On vehicles with an electronic immobiliser, comply with the diagnosis system instructions.

- In every control unit certain mean values are stored that are the basic values. The control unit receives different input values according to the engine condition. The teachable system compares the input values against the stored basic values and then forms the associated control commands. The control commands are forwarded to the corresponding actuators.
- When the DME control unit is de-energized for a long period (over one hour), the teachable system then loses the stored values. When a deleted control unit is returned to service or a new control unit is installed, the teachable system itself must read in and store the input value of the associated engine as new basic values.
- This process may cause uneven idle and faults in coasting mode after starting. Depending on the engine characteristics, it may take some time until all values have been compared with the engine condition.
- Therefore, comply with the following procedure before replacement or reinstallation of a DME/ DDE control unit is carried out:
1. If possible, bring the engine up to its operating temperature prior to replacement of the control unit.
2. Change control units and drive the vehicle with changing engine speeds.