Cooling Fan Control

The engine cooling fan system consists of an electrical cooling fan and 2 fan relays. The relays provides 2 separate voltage supply circuits to the electric cooling fan. The ground path is provided at G105. The cooling fan relays receive battery positive voltage and ignition 1 voltage from the underhood electrical center. They are controlled by the Powertrain Control Module (PCM).

During low speed operation, the PCM supplies the ground path for one of the cooling fan relays through the low speed cooling fan relay control circuit (Dark Green wire). This energizes the cooling fan relay coil, closes the relay contacts, and supplies battery positive voltage through the low speed cooling fan supply voltage circuit (Light Blue wire) to the electric cooling fan. There is an in-line resistor internal to the cooling fan that creates a lower voltage for the cooling fan to obtain low speed operation.

During high speed operation the PCM supplies the ground path for one of the cooling fan relays through the high speed cooling fan relay control circuit (Dark Blue wire). This energizes the cooling fan relay coil, closes the relay contacts, and provides battery positive voltage for the cooling fan through the high speed cooling fan supply voltage circuit (Gray wire).

The low speed cooling fan is commanded on when the coolant temperature reaches 226°F (108°C). It is turned off if the coolant temperature lowers to 219°F (104°C). The high speed cooling fan is commanded on when the coolant temperature reaches 235°F (113°C). It is turned off if the coolant temperature lowers to 226°F (108°C). When the A/C is on and the coolant temperature reaches 185°F (85°C), the low speed cooling fan will be turned on at vehicle speeds less than 35 mph.

If engine temperatures are to low for cooling fan operation the PCM will command the cooling fans to cool the A/C condenser. The low speed cooling fan will commanded on at 200 psi (1379 kPa). Then commanded off at 150 psi (1034 kPa). The high speed cooling fan will be commanded on at 230 psi (1586 kPa). Then commanded off at 215 psi (1482 kPa).