ECM

ECM







the ECM is located in the Environmental (E) box, in the front left corner of the engine compartment. the E-box provides a protective environment for the ECM and is cooled by an electric fan. the main relay for the ECM is also located in the E-box.

E-box







1 Fuse block
2 Cooling fan
3 Main relay
4 ECM
5 E-box temperature sensor
6 EAT ECU

A separate temperature sensor is used to monitor E-box temperature and provides a path to earth to control the electric fan. the sensor turns the fan on when the E-box temperature reaches 35°C and turns the fan off when the temperature drops below 35°C. the E-box fan draws air in from the passenger compartment, into the E-box and vents back into the passenger compartment. the fan is also driven for a short period on engine crank independently of temperature. This is done to ensure the correct function of the fan.

the ECM is programmed during manufacture by writing the program and the engine tune into a Flash Electronic Erasable Programmable Read Only Memory (EEPROM). the EEPROM can be reprogrammed in service using TestBook/T4. In certain circumstances it is possible to alter the tune or functionality of the ECM using this process.

Advanced fault monitoring is incorporated into the ECM. It can detect the type and severity of faults, store relevant engine operating conditions (environmental and freeze frame data) and time that a fault occurs, suspend the operation of some functions and replace the inputs from faulty sensors with default values. Environmental data is stored for each fault detected, and consists of the inputs from three engine sensors, with the inputs stored depending on the fault.

the ECM also records additional data in connection with each fault, as follows:

- the number of occurrences
- If the fault is currently present
- If the fault is historic, the number of drive cycles that have elapsed since the fault last occurred
- the time the fault occurred. Time is incremented in hours, hour 0 being the first time the ECM is powered-up, hour 1 being 60 minutes of ignition 'on' time, etc.

OBD freeze frame data is only stored for emissions related faults. Only one set of freeze frame data can be stored at any one time. Faults are prioritized according to their likely impact on exhaust gas emissions. If more than one emissions related fault occurs, freeze frame data is stored for the fault with the highest priority. Freeze frame data consists of the following:

- Engine speed
- Engine load
- Short term fuelling trim of LH and RH cylinder banks
- Long term fuelling trim of LH and RH cylinder banks
- Fuelling status of LH and RH cylinder banks
- Engine coolant temperature
- Road speed

Fault information is stored in a volatile Random Access Memory (RAM) in the ECM, so will be deleted if a power failure or battery disconnection occurs.

Five electrical connectors provide the interface between the ECM and the engine/vehicle wiring. the five connectors interlock with each other when installed in the ECM. Adjacent connectors should be disconnected in turn. the installation sequence is the reverse of removal. Each connector groups associated pins together.