Cooling Fan Description and Operation w/V8
Cooling Fan Control - Two Fan System
The engine cooling fan system consists of 2 puller type electrical cooling fans and 3 fan relays. The relays are arranged in a series parallel (S/P) 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. The ground path is provided at G104.
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 S/P 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. After a 3 second delay, the ECM supplies a ground path for the high speed fan relay and the cooling fan S/P relay through the high speed cooling fan relay control circuit. This energizes the cooling fan S/P 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.
The ECM commands the low speed cooling fans ON under the following conditions:
| • | Engine coolant temperature exceeds approximately 94.5°C (202°F). |
| • | A/C refrigerant pressure exceeds 1447 kPa (210 psi). |
| • | After the vehicle is shut OFF, if the engine coolant temperature at key-off is greater than 101°C (214°F), the low speed fans will run for a minimum of 60 seconds. After 60 seconds, if the coolant temperature drops below 101°C (214°F), the fans will shut OFF. The fans will automatically shut OFF after 3 minutes, regardless of coolant temperature. |
The ECM commands the high speed fans ON under the following conditions:
| • | Engine coolant temperature exceeds approximately 104.25°C (220°F). |
| • | A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi). |
| • | When certain DTCs set |
At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed, if required. This ensures idle stability by preventing the fans from cycling between high and low speed.
Cooling Fan Control - Three Fan System
The engine cooling fan system consists of a mechanical fan, 2 electrical pusher-type cooling fans, and 3 fan relays. The low speed, high speed, and series parallel (S/P) relays are arranged in an S/P configuration that allows the engine control module (ECM) to operate the left cooling fan and right cooling fan together, at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G104.
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 S/P 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. After a 3 second delay, the ECM supplies a ground path for the high speed fan relay and the cooling fan S/P relay through the high speed cooling fan relay control circuit. This energizes the cooling fan S/P 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.
The ECM commands the low speed fans ON under the following conditions:
| • | Engine coolant temperature exceeds approximately 94.5°C (202°F). |
| • | A/C refrigerant pressure exceeds 1447 kPa (210 psi). |
| • | After the vehicle is shut OFF, if the engine coolant temperature at key-off is greater than 101°C (214°F), the low speed fans will run for a minimum of 60 seconds. After 60 seconds, if the coolant temperature drops below 101°C (214°F), the fans will shut OFF. The fans will automatically shut OFF after 4 minutes, regardless of coolant temperature. |
The ECM commands the high speed fans ON under the following conditions:
| • | Engine coolant temperature exceeds approximately 104.25°C (220°F). |
| • | A/C refrigerant pressure exceeds 1824 kPa (265 psi). |
| • | When certain DTCs set |
At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed, if required. This ensures idle stability by preventing the fans from cycling between high and low speed.
Cooling Fan Description and Operation w/V6
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel (S/P) 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.
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 S/P fan 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 continues to supply battery positive voltage for the left cooling fan by grounding the coil of the low speed cooling fan relay. The ECM also grounds the high speed fan relay and the S/P fan relay through the high speed cooling fan relay control circuit. This energizes the S/P fan relay coil, closes the relay contacts, and provides a direct ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and providing battery positive voltage from the HI 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.
