The engine cooling fan system consists of an electric cooling fan, two fan relays and a fan resistor.

The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate the fan, the ECM 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 ECM applies ground to the coil side of the low speed FAN LOW relay. This energizes the coil and applies voltage directly to the engine cooling fan resistor through the switch side of the FAN LOW relay. The cooling fan is connected in series to the engine cooling fan. The series circuit operates the fan at low speed.

In high speed operation, the ECM applies a ground to the coil side of the high speed FAN HI relay. When energized, the FAN HI relay supplies voltage directly to the cooling fan through the switch side of the relay. With a direct voltage supply and path to ground the fan operates at high speed.