Radiator Cooling Fan Motor Relay: Description and Operation

Cooling Fan Control Circuit:

Purpose
The engine is equipped with two PCM controlled cooling fans. The secondary fan or auxiliary cooling fan is used for heavy duty cooling with A/C.


Operation
Primary Fan - When the engine is running, the PCM will turn "ON" the primary cooling fan for any of the following reasons:

^ Diagnostic Trouble Code (DTC) P0117, P0118 or P1530 is set.
^ Engine coolant temperature is 106°C (223°F) or greater
^ A/C is requested and vehicle speed is less than 50 mph
^ A/C refrigerant pressure is 190 psi or greater with A/C requested

Once the primary cooling fan is enabled, the PCM will turn the primary cooling fan "OFF" when:

^ Engine is turned "OFF"
^ Engine coolant temperature drops to 102°C (216°F) or less
^ A/C refrigerant pressure drops to 140 psi or less with A/C requested

Secondary Fan - When the engine is running the PCM will turn "ON" the secondary cooling fan for any of the following reasons:

^ Engine Coolant Temperature (ECT) is 112°C (223°F) or greater
^ A/C is requested and vehicle speed is less than 50 mph
^ A/C refrigerant pressure is 246 psi or greater

Once the secondary cooling fan is enabled, the PCM will turn the fan "OFF" when:

^ Engine is turned "OFF"
^ When the engine coolant temperature (ECT) sensor indicates the coolant temperature has dropped to 108°C (226°F) or less
^ When the A/C refrigerant pressure drops to 196 psi or less