Engine Control Module: Description and Operation
PRINCIPLE OF OPERATION, CONTROL MODULE (ECM)
The control module for the MOTRONIC 2.10.2 has 55 connecting pins and incorporates ignition and fuel injection control functions.
By means of input signals from a large number of sensors, the control module receives continuous information on engine load, temperature, engine rpm, exhaust gas composition, knocking (if occurring), etc.
The control module merges this information with the programmed maps in the permanent memory and utilizes the results to control both ignition and fuel injection.
The control module is located behind the panel by the right-hand A pillar. The wiring is run through grommets in the bulkhead partition to the engine bay. On removal of the power plant the control module connector and wiring is withdrawn through the bulkhead.
Manual/Automatic Programming
The MOTRONIC control module has the same part number for cars with a manual gearbox as for cars with automatic transmission.
By applying a voltage to pin 40, the control module is programmed for cars with automatic transmission.
On cars with a manual gearbox the circuit across pin 40 is open.
Coding the Control Module
By connecting different resistors across component 322 (Variant Coding) and pin 54, the control module is programmed to use different maps. On M94 cars the circuit across pin 54 is open.
Control Module Inputs
^ Mass air flow sensor
^ Engine temperature
^ Oxygen sensor
^ Crankshaft position sensor
^ Camshaft position sensor
^ Speed
^ Knock sensor
^ Throttle position sensor
^ DRIVE position
^ AC-ACC status
^ ICE (radiator fan)
^ Torque reduction
^ Power supply
^ Coding
^ Programming Man/Auto
^ Battery voltage +30 (memory)
^ Battery voltage +15 (ignition switch)
^ Grounding points
Control Module Outputs
^ Injectors
^ Engine rpm
^ Ignition pulses
^ AC compressor
^ Main relay
^ Fuel pump relay
^ CHECK ENGINE lamp (MIL)
^ Diagnostics
^ Throttle angle
^ EVAP canister purge valve
^ Idle air control valve (IAC)
^ Fuel consumption
^ Secondary air injection pump
^ Ground
Control Module Power Supply
When the ignition switch is turned to the DRIVE position and battery voltage is applied to pin 27 of the control module, pin 85 of the main relay is grounded via pin 36 of the control module, causing the relay to operate.
The control module then receives its main power supply on pin 37 from pin 87 of the main relay.
NOTE: Counted from the time the ignition is switched OFF, the relay remains in the operated state for about a further five seconds.
Battery Voltage +30
Battery voltage (+30) is applied to pin 18 of the MOTRONIC control module. The control module uses this voltage to supply the memory with keep-alive current. Power consumption in the idle state is less than 2.5 /mA.
NOTE: Unless the control module is supplied with +30 battery voltage, it will not be possible to start the car.
+15 Voltage
With the ignition switch in the DRIVE position, a +15 supply is applied to pin 27.
Among other things, the +15 supply is used to activate the control module so that it grounds the main relay, thus enabling a power supply to be applied to pin 37.
Power Ground, G7P
The control module is connected to power ground via pins 2, 14 and 24. The control module's main ground is applied to pin 14.
Lambda Reference Ground, G7L
The control module's reference ground for Lambda control is applied to pin 10.
Signal Ground, G7S
Pin 19 of the control module is connected to signal ground G7S. Also connected to signal ground are the camshaft and crankshaft position sensors, and the screening on the oxygen sensor's signal lead.
Sensor Ground
The control module grounds pin 30, which is the grounding point for the following sensors:
- throttle position sensor
- knock sensor
- coolant temperature sensor
Checking of Grounding Points
The difference in potential between the main ground on pin 14 and the sensor ground on pin 30 should be less than about 0.1 V.
A voltmeter can be used to check the control module's main ground by measuring the voltage across pin 14 and the negative battery terminal. A reading of less than about 0.1 V should be obtained. Other grounding points can be checked in the same manner, but the voltage should be measured across pin 14 and pins 2, 24, 10 and 19. A reading of less than about 0.1 V should be obtained here also.