The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the PWM signal. The cooling fan speed can be adjusted from 10 percent to 94 percent duty cycle. 94 percent is considered high speed fan.

The engine cooling fan system consists of one cooling fan and two relays. The cooling fan has 2 windings in the motor, one winding is for low speed and the other winding is for high speed. Voltage is supplied to the relays through fuses. The engine control module (ECM) controls the low speed fan operation by grounding the cool fan relay control circuit. When the cool fan, which is the low speed relay, relay is energized, voltage is delivered to the cooling fan low speed winding. The ECM controls the high speed fan operation by grounding the cool fan 2 relay control circuit. When the cool fan 2 relay, which is the high speed relay, is energized, voltage is delivered to the cooling fan high speed winding. The cooling fan motor is grounded through its own ground circuit.

When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10 mph. This is to prevent a fan from cycling ON and OFF excessively at idle.