Engine Control Module (ECM) 1 Glow plug relay 2 Engine compartment fusebox 3 Circulation fan 4 Main relay 5 ECM 6 EAT ECU The ECM has a steel casing to provide protection from electromagnetic radiation, and is located in the Environmental box (E-box). The ECM connected to the vehicle harnesses via 5 connectors. The ECM contains data processors and memory microchips. The output signals to the actuators are in the form of ground paths provided by driver circuits within the ECM. The ECM driver circuits produce heat during normal operation and dissipate this heat via the casing. The fan in the E-box assists with the cooling process by maintaining a constant temperature with the E-box. The fan is controlled by a thermostatic switch located in the E-box. The E-box has pipe connections to the vehicle interior and receives additional cooled air via the AC system. Some sensors receive a regulated voltage supplied by the ECM. This avoids incorrect signals caused by voltage drop during cranking.
ENGINE MANAGEMENT SYSTEM – TD 18-1-12 DESCRIPTION AND OPERATION The ECM performs self diagnostic routines and stores fault codes in its memory. These fault codes and diagnostics can be accessed using TestBook/T4. If the ECM is to be replaced, the new ECM is supplied 'blank' and must be configured to the vehicle using TestBook/T4. When the ECM is fitted, it must also be synchronised to the immobilisation ECU using TestBook/T4. ECM's cannot be 'swopped' between vehicles. The ECM is connected to the engine sensors which allow it to monitor the engine operating conditions. The ECM processes these signals and decides the actions necessary to maintain optimum engine performance in terms of driveability, fuel efficiency and exhaust emissions. The memory of the ECM is programmed with instructions for how to control the engine, this known as the strategy. The memory also contains data in the form of maps which the ECM uses as a basis for fuelling and emission control. By comparing the information from the sensors to the to the data in the maps, the ECM is able to calculate the various output requirements. The ECM contains an adaptive strategy which updates the system when components vary due to production tolerances or ageing. The ECM receives a vehicle speed signal on a CAN bus connection from the ABS ECU. Vehicle speed is an important input to the ECM strategies. The ABS ECU derives the speed signal from the ABS wheel speed sensors. The frequency of this signal changes according to road speed. The ECM uses this signal to determine the following: l How much to reduce engine torque during gear changes l When to permit cruise control operation l To control the operation of the cruise control l Implementation of the idle strategy when the vehicle is stationary.