Cooling Fan Supply (Description and operation)

On V8 engines the ECM will only enable the fan if the inlet air temperature is over 60 °C (140 °F). The ECM will allow the fan to run for a maximum of ten minutes, however the ECM continues to monitor the coolant temperature. The ECM logic will stop the fan if the coolant temperature is below the acceptable values stored in the ECM. To prevent a flat battery, the fan will be stopped (regardless of coolant temperature) if the battery voltage falls to 12 V.

Cooling Fan Supply

Circuit supply A permanent feed from the battery positive terminal is connected by an R wire to the engine compartment fusebox. A feed from this wire is connected to the contacts of the main relay and also to fuse 13. The feed passes through fuse 13 and to the inertia switch on a NB wire. The feed from the inertia switch flows on a WG wire to the engine compartment fusebox and is connected to the coils of the main relay. in this condition the coil and contacts of the main relay receive a permanent supply.

The permanent feed from the battery on a R wire to the engine compartment fusebox is also connected via fusible link 1 to fuse 5. From fuse 5 the permanent feed is connected to the contacts on the cooling fan relay. In this condition the contacts of the fan relay receives a permanent feed from the battery via fuse 5.

Main relay - ignition supply When the ignition switch is a position II, the ECM switches on the earth path for coil of the main relay. Current flows through the coil of the main relay and flows on a UR wire to pin C0635-23 V8/C0658-21 Td5 on the ECM. With the coil of the main relay energised the main relay contacts close, power is now available to the coil of the cooling fan relay, via the closed contacts of the main relay.