12 00 Contents of Engine Electrical System General

General Information

• Working on ignition system:
  1. Always switch off ignition before working on ignition system.
  2. Use only test leads which have been approved and belong to the testing instruments (e.g. DIS Tester).
  3. Comply with the country-specific safety regulations.
  4. Never touch components conducting current with engine running!
  5. Comply with instructions of DIS tester.
  6. Do not connect any suppression capacitors or inspection lamps to terminal 1 on the ignition coil.
  7. Terminal 1 of ignition coil must not be connected to ground or battery positive lead.
  8. If an alarm system is subsequently installed, lead of terminal 1 must not be used for start prevention.
  9. When working on ignition system, always disconnect supply leads to ignition coils.
  10. Caution: Hazardous voltages occur at: - Ignition lead, spark-plug connector, spark plug, ignition coil (high voltage at terminal 4 is approx. 40 kV) and lead of terminal 1 from ignition coil to DME control unit (high voltage approx. 350 V).
• Removing and installing electronic control units. Instructions for removing and installing electronic control units:
  1. 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.
  2. Control unit plugs should only ever be connected and disconnected while the ignition is turned off.
  3. 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.
  4. Investigate stored faults and, once any faults have been remedied, cancel the fault memory.
  5. Always read out hardware/software version of the corresponding control unit with DIS tester.
  6. Comply with the instructions of the DIS tester on the steps coding and programming.
  7. On vehicles with electronic vehicle immobilization, comply with the instructions of the DIS tester.
  8. 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.
  9. 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.
  10. 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.
  11. Therefore observe the following procedure before replacing or reinstalling a DME/DDE control unit: If possible before exchanging control unit, run engine up to operating temperature. Turn ignition off. Remove the control unit, install a new control unit and operate vehicle at different engine speeds.
• Welding work (overload protection of control units):
  1. Detach terminal of battery negative lead from car battery and second battery if fitted. Cover negative terminal posts.
  2. If welding is to be performed near the battery/batteries, first remove battery/batteries from vehicle (flying sparks - combustion of explosive gas).
  3. Fit return clamp on welding unit as close as possible to welding point (maximum distance approx. 1 m).
  4. Never connect return clamp to ground pin on body which has ground wires attached!
• Disconnecting and connecting battery. See 12 00... Instructions for disconnecting and connecting battery .
• Disconnecting and connecting test equipment. Follow operating instructions for testing devices. Make sure that connected test leads cannot make contact with rotating parts (e.g.: fans, ribbed V-belts, etc.).
• Component inspection. Always disconnect connectors of control units or components before checking electric wires.
• External jump-starting aid.
• Compression testing. See 11 00 039 CHECKING COMPRESSION OF ALL CYLINDERS .