Fuel pump relay (Engine management system - Td5)

Fuel pump relay

The fuel pump relay is located in the engine compartment fuse box. It switches on the fuel pump to draw fuel from the fuel tank to the electronic unit injectors (EUI).

Input/Output The fuel pump relay is a 4 pin normally open relay. Voltage input to the fuel pump relay comes from the main relay switching contacts. When the main relay is energised the switching contacts close and the fuel pump relay windings are supplied a voltage. The ECM provides the earth for the relay windings to close the relay contacts and operate the fuel lift pump. The fuel pump relay switching contacts are supplied voltage via fuse 10 located in the engine compartment fuse box. Output from these switching contacts is supplied directly to the fuel pump. When the ECM interrupts the earth the return spring in the relay pulls the contacts apart and the fuel lift pump stops operating. The earth path is via pin 5 of ECM connector C0658.

The fuel pump relay can fail in the following ways: l Relay open circuit. l Short circuit to vehicle supply. l Short circuit to vehicle earth. l Broken return spring.

In the event of a fuel pump relay failure any of the following symptoms may be observed: l Engine will crank but not start. l If the engine is running it will stop.

The MIL will not illuminate in a fuel pump relay failure.