Cooling Fan Description and Operation Gas w/o LFA
Cooling Fan Control - Two Fan System
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 receive positive voltage from the cooling fan relays which receive battery positive voltage from the underhood fuse block. The fan relay coils receive ignition 1 voltage from the powertrain relay.
During low speed operation, the ECM supplies the ground path for the low speed fan relay 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 low 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 cooling fan series/parallel relay 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 grounds the high speed fan relay and the cooling fan series/parallel relay through the high speed cooling fan relay control circuit. This energizes the cooling fan control relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high 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.
Refer to Engine Cooling Schematics.
Cooling Fan Description and Operation w/ LFA
Hybrid Cooling Fan Control - Two Fan Five Relay System
The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.
During low speed operation, the ECM supplies the ground path for the low fan relay control circuit. This energizes the low fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low 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 de-energized fan control relay, through the right cooling fan in-line resistor, and through the right cooling fan. The result is a series circuit with both fans running at low speed.
During medium speed operation the ECM grounds one control circuit that energizes a bank of three relays consisting of the FAN Mid 1 relay, the fan control relay, and the FAN Mid 2 relay. When these three relays are energized the Mid 1 relay supplies battery voltage to the left cooling fan through the left cooling fan resistor. A ground path is provided for the left fan through the energized fan control relay. At the same time the Mid 2 relay is energized which applies battery voltage to the right cooling fan through the right cooling fan resistor. The result is a parallel circuit where each fan has voltage applied through a resistor which causes each fan to operate at reduced speed.
During high speed operation the ECM grounds all three relay control circuits which activates all five relays. This allows full battery voltage to be applied to the right cooling fan from the high fan relay, and full battery voltage to be applied to the left fan from the low fan relay. The left fan is grounded through the fan control relay. In this arrangement each fan has full battery voltage applied and each fan has its own ground path. The result is a parallel circuit with both fans running at high speed.
Refer to Engine Cooling Schematics.
