12 00 Contents of Engine Electrical System General

General Information

Working on ignition system
1. Always switch off ignition before working on ignition system.
  Never touch components under current with engine running!
  
  Dangerous high tension!
2. Always remove DME master relay for the compression test to avoid activation of ignition coils by ignition final stages of the DME control unit.
  Dangerous high tension!
3. Always switch off ignition before connecting /disconnecting Service Tester, other testers and adapters or replacing components!
4. The secondary side (high voltage side) of ignition system must be under load of at least 4 kΩ.
5. Never start engine after removing distributor cap or disconnecting wire (terminal 4) on ignition coil (terminal 4).
6. Never connect a shielded capacitor or test light on ignition coil terminal 1.
7. Never connect ignition coil terminal 1 wire earth or battery positive.
  For this reason, terminal 1 wire may not be used to interlock starting when service installing a burglar alarm system.
Removing And Installing Electronic Control Units
CAUTION: Disconnecting the vehicle battery will cancel the fault memories of control units.

For this reason, before disconnecting the battery, connect up BMW SERVICE TESTER or DIS. DIS: (select Expert mode) interrogate fault memory and print out fault messages stored in memory. BMW SERVICE TESTER: Interrogate fault memory and print out fault messages stored in memory. Investigate stored faults.

Ignition must always be switched off before disconnecting or connecting control-unit connectors.

Removal and installation of components, relays, fuse, etc. could cause the storage of faults in fault memories of control units capable of self-diagnosis. For this reason, fault memories must always be interrogated after working on the electrical system. Stored faults must be investigated and cancelled.

When Replacing Control Unit Of DME (Digital Motor Electronics), Please Note The Following Points:

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. 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-commissioning a cancelled unit or installing a new control unit, the input values of the relevant 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.

For this reason, follow the procedure described below before replacing or reinstalling a DME control unit:
1. Run engine to operating temperature if possible before replacing the control unit.
2. Remove control unit, install new control unit and drive vehicle.
Welding Work (Overload Protection Of Control Units)
When performing welding work on installed control units, to avoid any defects in the electronic control units, observe the following steps:
- Observe instructions for disconnecting and connecting battery. See INSTRUCTIONS FOR DISCONNECTING AND CONNECTING BATTERY.
- Detach terminal of battery negative lead from car battery and second battery if fitted. Cover negative terminal posts.
- If welding is to be performed near the battery/batteries, first remove battery/batteries from vehicle (flying sparks - combustion of explosive gas).
- Fit return clamp on welding unit as close as possible to welding point (maximum distance approx. 1 mm).
- Never connect return clamp to ground pin on body which has ground wires attached!
Disconnecting and connecting battery .
Observe safety instructions for handling vehicle battery. Refer to Safety Instructions For Handling Vehicle Battery .

Before Disconnecting Battery:

Switch off ignition.

NOTE: If the ignition is not turned off when the battery is disconnected, fault memories may be set in some control units.

Important!
- There is a danger of mixing up battery leads: If the battery positive and negative leads are the same color and you are in doubt, follow the polarity to the battery, then mark and cover the leads.
- On vehicles with radio code: After disconnecting the battery, the radio code must be re-entered. Therefore obtain the radio code card from the customer beforehand. Note stored stations and restore them after connecting the battery.
- Stored settings of the on-board computer and clock will also be lost.
- All available central keys must be receded for cars with first generation infrared transmitter locking systems.
General Notes On Disconnecting Battery:
- Do not disconnect battery leads and leads from alternator and starter motor while engine is running.
- Cars with IBS on battery negative terminal:
- Do not under any circumstances pull/lever off pole shoes by force.
- Do not under any circumstances release socket-head cap screw of IBS.
- When work is carried out on the electrical system, faults may be caused in the fault memories of some control units when the battery is connected.
After Connecting Battery:

Important!

After a power supply interruption some equipment is disabled and must be reactivated.

For further information and instructions on vehicle-specific activation, please refer to PROCEDURE FOR INITIALIZATION .
Disconnecting and connecting test equipment
When connecting and disconnecting:
- Service Tester.
- Testing Devices.
- Test Leads.
- When Replacing Control Units.
It is essential to turn off the ignition.

Follow instructions for removing and installing electronic control units. See REMOVING AND INSTALLING ELECTRONIC CONTROL UNIT.

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
NOTE: On all inspections and operations on the engine electrics and electronics, comply with prevailing national safety legislation and accident prevention regulations.

Always disconnect connectors of control units or components before checking electric wires.

Testing Aids:

The relevant wiring diagrams are filed in the Electrical Troubleshooting Manual folder for the 3 Series E36.

Always use correctly produced inspection lines, adapters, terminals and test tips.

Test values for checking components are contained in the Electrical Troubleshooting Manual.

For further technical information, refer to ENGINE ELECTRICAL SYSTEM - TECHNICAL DATA .
External Jump-Starting Aid
Do not start the engine with help of starting sprays.

Preparation

Conform with the following when starting engine with starting cable.

Ensure that starting cable wires are to appropriate cross-section size.

Only use fuse-protected starting cables.

Check whether the current supplying battery has 12V voltage.

If engine is started from battery of another vehicle, ensure that there is no contact between the bodies of both vehicles.

CAUTION: Never touch ignition system components under current - dangerous high tension!

Operation:

Always conform with the procedures to avoid injury to persons or damage to parts.

Select range P in vehicles with an automatic transmission and apply the parking brake.

Move the shift lever of vehicles with manual transmission into neutral and apply the parking brake.

Ensure that the starting cables cannot get caught in rotating parts, e.g. fan.

First connect both positive poles of the batteries with one starting cable (red).

Use the positive connection point in the engine compartment for vehicles with the battery in the trunk.

Then connect the second starting cable (black) between the negative pole of the current supplying battery and engine or body earth of the vehicle to be started.

CAUTION: Never connect the second starting cable (black) on the negative pole of the battery in the vehicle to be started. Produced gas could be ignited by sparks.

Danger of explosion!

If the battery in the vehicle supplying power is weak, start the engine of this vehicle and let it run at idling speed.

After the engine of the vehicle to be started has started up, first disconnect the starting cable on the negative pole/earth connection. Then remove the starting cable from the positive poles.
Compression Testing See 11 00 039 CHECKING COMPRESSION OF ALL CYLINDERS .