General Description

Engine Control Module (ECM) - (from 99MY)
From 99MY the Engine Control Module (ECM) is a Bosch Motronic 5.2.1. which is mounted in a plastic "E-box" located on the LH side of the engine bay bulkhead. The ECM is cooled by a dedicated fan, which supplies cabin air into the plastic E-box to provide a suitable temperature environment for the ECM. The working temperature of the ECM is monitored by an internal temperature sensor.




A. 9-pin connector (C0634)
B. 24-pin connector (C0635)
C. 52-pin connector (C0636)
D. 40-pin connector (C0637)
E. 9-pin connector (C0638)

The E-box is a moulded black plastic case which houses the ECM and protects it from sources of contamination. The ECM itself is contained in a cast aluminium case. The ECM has 5 independent connectors totalling 134 pins, of which up to 79 are used, dependent on market variations. The ECM and connectors can be accessed by positioning the cruise control pneumatic actuator and pump assembly aside, lifting the two plastic clips at the top of the e-box and pulling the E-box lid upwards and out. The ECM is held in position in the lid of the box by two plastic brackets. The ECM connectors have to be disengaged sequentially to release them from the unit. Similarly, when the connectors are reconnected to the ECM, the correct sequence must be observed.




Connectors C0634 and C0638 are square type and have release buttons on their front face which have to be pressed to enable them to be removed.




Connectors C0635, C0636 and C0637 are angled and have release buttons located on the top face. The release buttons have to be pressed and the locking levers pulled back to enable the connectors to be disconnected from the ECM. Each of the connectors have two integral blocks, one grey and one black, which can be removed from the connector housing to enable access to the back of the plugs. Block removal is achieved by pressing the locking tags and sliding the connector blocks outwards.

The E-box lid has two location tags on the bottom edge which have to be aligned with the corresponding holes in the E-box case before clipping the top of the lid into position. Care should be taken not to trap any wires when closing the E-box lid.

The ECM uses a "flash" electronic erasable programmable read only memory (EEPROM). This enables the ECM to be externally configured, to ensure that the ECM can be updated with any new information; this also allows the ECM to be configured as many times as is necessary to meet changing specifications and legislation.

The ECM memorises the positions of the crankshaft and the camshaft when the engine has stopped via the CKP and CMP sensors. This allows immediate sequential fuel injection and ignition timing during cranking. This information is lost if battery voltage is too low (i.e. flat battery). So the facility will be disabled for the first engine start after battery reconnection.

The ECM has various sensors fitted to the engine to allow it to monitor engine condition. The ECM processes these signals and decides what actions to carry out to maintain driveability, after comparing the information from these signals to mapped data within its memory.

CAUTION: Do not connect test probes connected to battery positive supply to any ground pins on the ECM. THIS MAY DESTROY THE ECM.