Engine management (MEMS 3), fuel and emission systems (Vehicle Immobilisation): Description and operation

Vehicle Immobilisation

The vehicle immobilisation system operates by the alarm ECU transmitting a unique code to the ECM when the ignition is switched on. If the code is recognised by the ECM it will energise the injectors and allow the engine to start.

If no code is received or the code is incorrect, the ECM will disable the vehicle by not energising the fuel injectors.

The alarm ECU also controls the starter relay and will passively disarm the starter relay when the key is removed from the ignition switch. Rearming is performed by turning the ignition on which activates a coil around the ignition key barrel.

The coil transmits a waveform signal which excites the remote handset to transmit a re-mobilisation signal. When the signal is received by the alarm ECU, the starter relay will be enabled.

Replacement ECM’s are supplied blank and must learn the alarm ECU security code for the vehicle to which it is fitted. When the ECM is connected to the vehicle, TestBook is required to enable the ECM to learn the alarm ECU code. If a new alarm ECU is fitted, the ECM will need to learn the new security code using TestBook.

Rough Road Detection

MEMS 3 has a misfire detection facility which is part of the On-Board Diagnostics (OBD) system. Misfire detection is disabled when the ECM senses that the vehicle is on a ’rough road’. The system software can detect variations in the signal output and disable misfire detection to prevent incorrect faults being logged by the ECM.

The ’rough road’ signal is passed from the ABS ECU on a hardwired output to the ECM pin 78. The signal is in the form of a square wave digital pulse train of between 0 and 5 V at 8000 pulses per mile.

On vehicles without ABS, an ABS reluctor ring is fitted to the LH rear wheel and provides 48 pulses per rotation of the wheel to a variable reluctance sensor. The output from the sensor is received by ECM pin 78 and the sensor is provided with a positive supply signal from ECM pin 64.

Fuel Pump

The electric fuel pump is located inside the fuel tank and is energised by the ECM via the fuel pump relay in the engine management relay module and the inertia switch.

The fuel pump delivers more fuel than the maximum load requirement for the engine, maintaining pressure in the fuel system under all conditions.