The engine cooling fan system consists of an electric cooling fan, two fan relays and a fan resistor. The fan 1 relay provides power to the fan motor. The fan 2 relay controls the ground path of the fan motor.

The powertrain control module (PCM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate the fan, the PCM applies ground to the coil side of the applicable fan relay. This energizes the coil and pulls the switch side of the relay closed.

In low speed operation, the PCM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the fan 1 relay. The cooling fan is connected in series to the fan resistor through the de-energized fan 2 relay. The series circuit operates the fan at low speed.

In high speed operation, the PCM applies a ground to the coil side of the low speed fan  relay and the high speed fan 2 relay. When energized, the fan 2 relay a provides a direct path to ground for the cooling fan through the switch side of the relay. Simultaneously, the fan 1 relay continues to provide ignition voltage to cooling fan which enables the fan to operate at high speed.

High speed fan operation can also occur in response to A/C system operation. The A/C refrigerant pressure switch is in parallel with the PCM controlled ground for the coil of the fan 2 relay. If the A/C system pressure exceeds 1520 kPa (220 psi), the pressure switch closes the ground circuit to the coil of the fan 2 relay, initiating high speed fan operation.