Engine Cooling Fan Control

The engine's electric cooling fan is controlled by the engine control module (ECM). When the air conditioning (A/C) compressor is engaged the automatic temperature control (ATC) module sends a fan speed message between 0 (off) and 15 (maximum speed) to the ECM, via the K bus, instrument cluster and high speed controller area network (CAN) bus. The automatic temperature control (ATC) module requests the cooling fan on when:

• The vehicle speed is less than 70 km/h (44 mph).
• There is no fault with the air conditioning (A/C) compressor clutch circuit.
• Battery voltage is less than 16 V.

The fan speed requested depends on the pressure in the refrigerant system. The higher the pressure the faster the fan speed that is requested. When vehicle speed increases to more than 80 km/h (50 mph) the automatic temperature control (ATC) module changes the fan speed request to 0 until vehicle speed decreases to less than 70 km/h (44 mph) again.

If battery voltage increases to more than 16 V for 5 seconds the automatic temperature control (ATC) module changes the fan speed to 0 until the voltage decreases to less than 15.8 V.