TD5 Defender
ENGINE MANAGEMENT SYSTEM
21
DESCRIPTION AND OPERATION
RELAY - FUEL PUMP
The fuel pump relay is located in the engine compartment fuse box. It switches on the fuel pump to draw fuel from
the tank to the electronic unit injectors (EUI).
Input / Output
The fuel pump relay is a 4 pin normally open relay. The fuel pump relay (C0730-4) is provided with a feed by the
main relay (C0063-78) via header 291 on a brown/orange wire. An earth path is provided for the fuel pump relay
(C0730-6) via the ECM (C658-5) on a blue/purple wire. This energises the fuel pump relay and allows a feed to be
provided to the fuel pump. When the ECM interrupts the earth, the relay is de-energised and the fuel pump stops
operating.
The fuel pump relay can fail in one or more of the following ways:
•
Relay open circuit.
•
Short circuit to vehicle supply.
•
Short circuit to vehicle earth.
•
Broken relay return spring.
In the event of a fuel pump relay failure any of the following symptoms may be observed:
•
Engine will crank but not start.
•
If the engine is running, it will stop.
RELAY - MAIN
The main relay is located in the engine compartment fuse box and supplies battery voltage to the following:
•
The ECM.
•
The MAF sensor.
•
Fuel pump relay.
Input / Output
The main relay is a 4 pin normally open relay, which must be energised to provide a voltage to the ECM. The main
relay (C0063-86) is provided with an earth path via a transistor within the ECM (C0658-21) on a blue/red wire.
When the earth path is completed, the relay is energised and supplies the ECM (C0658-3, C0658-22 & C0658-27)
with a feed on brown/orange wires via header 291.
The main relay can fail in the following ways:
•
Relay open circuit.
•
Short circuit to vehicle supply.
•
Short circuit to vehicle earth.
•
Broken relay return spring.
In the event of a main relay failure any of the following symptoms may be observed:
•
Engine will crank but not start.
•
If the engine is running, it will stop.
For the ECM start up to take place the ignition feed when the switch is in position ’II’ must be greater than 6.0
volts.