Fuel Pump Relay

Fuel Pump Relay

The fuel pump relay is located in the engine management relay module which is positioned behind the ECM mounting bracket. The relay is normally open when the ignition is off.

When the ignition is switched on to position II, the ECM provides an earth path for the relay coil. With the ignition on the relay receives a feed, via the ignition switch, from fuse 14 in the passenger compartment fusebox which energises the relay coil, closing the contacts.

A permanent battery supply is provided to the relay contacts from fuse 2 in the under bonnet fusebox, via the inertia switch. The feed passes through the relay contacts and operates the fuel pump to pressurise the fuel system. The relay will be energised for a short time only to pressurise the fuel system.

When the ignition switch is moved to the crank position III, the ECM will energise the relay when the engine starts cranking and will remain energised until the engine stops.

If the engine stalls and the ECM stops receiving a signal from the CKP sensor, the ECM will remove the earth path for the relay, stopping the fuel pump.

WARNING: ALWAYS check for fuel leaks and the integrity of the fuel system before resetting the inertia switch.

The inertia switch, when tripped, cuts off the power supply to the relay contacts, disabling the fuel pump in the event of a sudden deceleration. If the fuel pump fails to operate, check that the inertia switch is not tripped. The switch is reset by depressing the rubber cap on the top of the switch.

If the fuel pump relay fails, power will not be supplied to the fuel pump and the engine will not start or will stop if already running due to fuel starvation. The ECM will store fault codes which can be retrieved using TestBook.

A/C Compressor Clutch Relay (Where Applicable)

On vehicles fitted with air conditioning, an A/C relay module is located under the bonnet adjacent to the under bonnet fusebox. When the engine is running and the driver requests A/C on, the ECM receives a signal from the A/C switch to pin 56.

If conditions are correct, the ECM grants the A/C request by completing an earth path from pin 54 to the A/C clutch relay coil. The A/C clutch relay coil receives a battery feed from the ignition switch position II. The feed is supplied via fuse 15 in the passenger compartment fusebox to the relay coil. The coil will energise closing the relay contacts.

A permanent battery supply, via fuse 5 in the under bonnet fusebox, passes through the relay contacts and operates the compressor clutch.

The ECM will disengage the A/C compressor clutch if the coolant temperature exceeds 118°C (244°F) and will re-engage the A/C compressor clutch when the coolant temperature falls to less than 114°C (237°F).

If the A/C clutch relay fails, the A/C will be inoperative and the ECM will store fault codes which can be retrieved using TestBook.