Cooling Fan Control

WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

The engine cooling fan system consists of 2 electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) 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 G100.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the fan 1 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 fan 2 relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the fan 2 relay and the fan 3 relay through the high speed cooling fan relay control circuit. This energizes the fan 2 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the fan 3 relay coil is energized closing the relay contacts and provides battery positive voltage from the fan 2 fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

The PCM commands Low Speed Fans on under the following conditions:

Engine coolant temperature exceeds approximately 100°C (212°F)
When air conditioning (A/C) is requested and the ambient temperature is more than 4°C (39°F)
A/C refrigerant pressure exceeds 1241 kPa (180 psi)
After the vehicle is shut off if the engine coolant temperature at key-off is more than 117°C (242°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans on under the following conditions:

Engine coolant temperature exceeds approximately 105°C (221°F)
A/C refrigerant pressure exceeds 1655 kPa (240 psi)
When certain DTCs set
The PCM will command the cooling fans ON at any vehicle speed when the engine coolant temperature exceeds approximately 123°C (254°F)