Removing And Installing Electronic Control Units

Instructions for removing and installing electronic control units: 

• 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.
• Comply with the following when replacing the DME/DDE (Digital Motor Electronics/Digital Diesel Electronics):
  • Always read out hardware/software version of the corresponding control unit with DIS tester. Comply with the instructions of the DIS tester on the steps coding and programming. On vehicles with electronic vehicle immobilization, comply with the instructions of the DIS tester.
  • Each control unit is programmed 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. The control commands are routed to the relevant actuators.
  • If, for example, the DME control unit were without current for a long time (more than an hour), its adaptive system would lose the stored values. When a cleared control unit is restarted or a new control unit is installed, the adaptive system must read in and store the input values of the associated engine as new basic values itself.
  • 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.
  • Therefore observe the following procedure before replacing or reinstalling a DME/DDE control unit:
    1. If possible before exchanging control unit, run engine up to operating temperature.
    2. Remove the control unit, install a new control unit and operate vehicle at different engine speeds.