Cooling Fan Description and Operation LAT

The engine cooling fan system consists of one cooling fan and two relays. Voltage is supplied to the relays through the 30A MAIN FAN and 30 A AUX FAN fuses. The engine control module (ECM) controls the low speed fan operation by grounding the AUX FAN relay control circuit. When the AUX FAN relay, which is the low speed relay, is energized, voltage is delivered to the cooling fan Cooling Fan Resistor. The ECM controls the high speed fan operation by grounding the MAIN FAN relay, which is the high speed relay, control circuit. When the MAIN FAN relay is energized, voltage is delivered directly to the cooling fan. The cooling fan motor is grounded through its own ground circuit.

The low speed cooling fan supply voltage circuit passes through a single 0.3 ohms cooling fan motor resistor. The resistor assembly is serviceable.

Cooling Fan Description and Operation Except LAT

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

During low speed operation, the ECM supplies the ground path for the low speed fan relay, which is AUX fan relay 12, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the AUX fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the series/parallel relay, which is the fan control relay 15, and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The ECM supplies a ground path for the high speed fan relay, which is the main fan relay 16 and the series/parallel through the high speed cooling fan relay control circuit. This energizes the series/parallel relay coil, closes the relay contacts, and provides a ground path for the left cooling fan relay. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the main fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.

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.