General description (Peugeot Eurovans 806)

Electronic engine management system (EMS) Bosch Motronic MP3.2, which has been used to control Citroen and Peugeot engines since around 1993, is an integrated system that controls ignition coil primary, fuel delivery and idle speed control through the same electronic control unit (ECM) (see illustration 11.1). The MP3.2 is an upgraded version of the MP3.1 that has increased the number of ECM pins from 35 to 55.



Electronic control unit (ECM) simultaneously determines the ignition timing and duration of fuel injection. Thus, the best moment of ignition and fuel supply is determined. The Bosch Motronic system uses the same fuel injection functions as the L-Jetronic system. Using a 55-pin multi-pin connector, the electronic control unit is connected to the battery, sensors and actuators.

Main functions of the electronic control unit (ECM) (MPi)

DC voltage is supplied from the battery to the pin number 18 of the electronic control unit. This allows the self-diagnosis program to save data. With the ignition on, the main fuel injection system relay supplies voltage to ECU pin #37, as well as to the fuel injectors and the idle air control valve (ISCV).


Most sensors (unlike those that produce voltage, for example: crankshaft angle sensor (CAS), oxygen sensor (OS)) now receive a voltage of 5.0 Volts from the corresponding contact pin of the electronic control unit. When the crankshaft is cranked or the engine is running, the signal from the crankshaft angle sensor (CAS) causes the ECM to ground pin #3 so that the relay starts to energize the ignition coils and the fuel pump. If the crankshaft continues to crank, the ECM will close each drive circuit by pulsing the appropriate ground wire, and the injector, idle control valve (1SCV), the ignition coils and the fuel pump will start working.

Reference voltage

The initial voltage level supplied from the electronic control unit to many sensors is 5.0 volts.

Power supplies for the electronic control unit (ECM) and grounding checks

Rated battery voltage (nbv)

State	Volts
Ignition on	11.5-13.5
When turning the crankshaft	8.0 +
On a running engine	13.0-15.9

Voltage values of the electronic control unit (ECM)

Terminal numbers

ECM	Element	State	Volts
18	Battery: t30	Ignition off	nbv
37	Relay output terminal	Ignition on	nbv
36	Relay control circuit	Ignition off	nbv
36	Relay control circuit	Ignition on	1.25 (maximum)
3	Relay control circuit	Ignition on	nbv
3	Relay control circuit	When cranking/engine running	1.25 (maximum)
14, 19, 24 and 47	ECM ground	Ignition on	0.25 (maximum)

Note, nbv is the nominal battery voltage (see illustrations 11.2, 11.3, 11.4, 11.5, 11.6)