3.5L & 4.0L Aurora: Description

Engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. Relays are arranged in a series/parallel configuration that allows Powertrain Control Module (PCM) to operate both fans together at low or high speeds. Cooling fan relays receive battery voltage from underhood fuse block.

During low speed operation, PCM supplies ground path for low speed fan relay through low speed cooling fan relay control circuit. This energizes cooling fan 1 relay coil, closes relay contacts, and supplies battery voltage from cool fan 1 fuse through cooling fan motor supply voltage circuit to right cooling fan. Ground path for right cooling fan is through cooling fan series/parallel relay and left cooling fan. Result is a series circuit with both fans running at low speed.

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

PCM commands Low Speed Fans on under the following conditions:

• Engine coolant temperature exceeds approximately 223°F (106°C).
• Fans will switch from low to off when coolant drops less than 216°F (102°C).
• A/C operation is requested.
• After vehicle is shut off, if coolant temperature at key-off is more than 304°F (151°C) and system voltage is more than 12 volts. Fans will stay on for approximately 3 minutes.

PCM switches fans to high speed under the following conditions:

• Engine coolant temperature reaches 234°F (112°C).
• A/C refrigerant pressure exceeds 240 psi.
• Fans will return to low speed operation if refrigerant pressure drops less than 190 psi.
• When certain DTCs set.