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

Relay module

The relay module is located in the engine compartment adjacent to the engine control module. The relay module contains the following relays:

• Main relay - energised when the ignition is switched on and supplies power to the ECM.
• 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.
• Heated oxygen sensor relay - energised by the ECM and supplies current to the heated oxygen sensor element.

Purge valve

The purge valve is an integral part of the EVAP canister, and is driven directly from the ECM. When the purge valve is opened it allows the EVAP canister to vent into the engine inlet manifold. The valve is opened by the ECM for varying periods under specific engine conditions to avoid degrading engine performance.

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 relay module and the fuel cut-off 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.