Engine Control Module: Description and Operation

PRINCIPLE OF OPERATION
The Motronic primarily controls
- the ignition (by means of the ignition coil module)
- fuel injection (which is sequential)

The Motronic control module has a 55-pin connector and is located in the engine bay behind the bulkhead partition on the left-hand side.

On removal of the power train the control module connector and wiring are withdrawn through the bulkhead partition.

A number of sensors supply the control module with information which it processes by means of programmed maps stored in its memory after optimization of engine performance.

These important maps are used to control ignition timing and fuel injection. The control module is programmed for the B308 engine and should be used for this engine only.

The control module can be damaged by electrostatic discharges or a short circuit on any of its outputs. For this reason it must always be handled with great care when carrying out fault diagnosis and fitting spare parts.

The control module is supplied continuously with +30 voltage and will lose its adapted values if this voltage disappears. Diagnostic trouble codes will not disappear as these are stored in a non-volatile memory.

Adaptation is important for performance, DRIVEABILITY, fuel consumption and emissions. The ECM must therefore not be unnecessarily disconnected or in any other way de-energized.





Turning the ignition switch to the ON position activates the control module which grounds pin 46 and causes the main relay to operate. The control module then waits for signals from the crankshaft position sensor.

The principal measured quantity for fuel injection comes from the mass air flow sensor. Substitute functions are provided for all sensors except the crankshaft position sensor.

The control module remains active for a certain period of time after the ignition switch has been turned to the OFF position. If the engine is restarted during this period no pre-injection will take place when the starter motor begins to turn the engine over.

Manual/Automatic
The electronic control module has the same part number for cars with a manual gearbox as for those with automatic transmission.

When a gear position other than P or N is selected on cars with automatic transmission, positive battery voltage will be applied to pin 42 and the idle air control valve will open a little more to compensate for the increase in load.

Pin 42 is not connected on cars with a manual gearbox.





Control Module Power Supply
+30
Pin 18 of the control module is supplied with +30 voltage via fuse 23.
The control module uses +30 for its memory. The engine will not start without +30.

+15
Pin 27 of the control module is supplied with +15 voltage via fuse 13.
When +15 is applied to pin 27 the control module is activated, grounding pin 46 and causing the main relay to operate. The main relay supplies the control module with positive battery voltage on pin 37.
The engine will not start without +15 or if no voltage is present on pin 37 of the control module.

NOTE: When the ignition switch is turned to the OFF position the main relay remains operated for a further five seconds if the coolant temperature is above -4°C (25°F). At lower temperatures the main relay remains operated for 30 seconds.





CONTROL MODULE INPUTS
1. Battery voltage +30 (memory)
2. Battery voltage +15 (ignition switch)
3. Main relay
4. Ground
5. Crankshaft position sensor
6. Camshaft position sensor
7. Mass air flow sensor
8. Throttle position sensor
9. Coolant temperature
10. Intake air temperature
11. Knock sensors
12. Car speed
13. DRIVE position on cars with automatic transmission
14. Oxygen sensors
15. A/C - ACC status
16. TCS control (active)
17. Diagnostics





CONTROL MODULE OUTPUTS
1. Ground
2. Ignition pulses
3. Injectors
4. Idle air control valve
5. Main relay
6. Fuel pump relay
7. Solenoid valves for variable intake manifold
8. EVAP canister purge valve
9. Secondary air injection pump
10. Engine rpm
11. Throttle position
12. Fuel consumption
13. A/C compressor
14. MIL (CHECK ENGINE) indicator lamp
15. Diagnostics