Engine management system - MEMS (Relay Module): Description and operation

Relay Module

The relay module is located in the engine compartment behind the ECM. The relay module contains the following relays:

• Main relay - energised by the ECM when the ignition is switched on and supplies power to the ECM. The ECM controls the main relay and will maintain the main relay in an energised state for a predetermined period after the ignition is switched off. This allows time for the ECM to ’power down’ and prepare itself for the next engine start.
• Fuel pump relay - energised by the ECM for a short period when the ignition is switched on, during cranking and while the engine is running.
• Starter relay - energised by the cranking signal from the ignition switch via the CCU and supplies power to the starter motor solenoid.
• Heated oxygen sensor relay - energised by the ECM and supplies current to the heating element of the heated oxygen sensor.

Fuel Pump

The fuel pump is installed in a unit located inside the top face of the fuel tank. It is accessible by raising the rear passenger seat and removing a sealed cover plate. The electric fuel pump is located inside the fuel tank and is energised by the ECM via the fuel pump relay in the relay module via the inertia fuel shut-off (IFS) switch.

The fuel pump delivers more fuel than the maximum load requirement for the engine, pressure is therefore maintained in the fuel system under all conditions. A fuel pressure regulator is located in the same housing as the fuel pump.

Fuel Pressure Regulator

The fuel pressure regulator is a mechanical device located in the tank unit with the fuel pump.

The regulator is connected to the fuel delivery pipe from the pump and ensures that constant fuel pressure in the fuel line is maintained. When pressure from the pump exceeds the regulator setting, the pressure overcomes an internal spring in the regulator and fuel is returned to the fuel pump swirl pot.