3.8L Engine

WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo and 2002 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

The engine cooling fans are controlled by the Body Control Module (BCM) and the Powertrain Control Module (PCM). The BCM sends a Class 2 message to the PCM requesting cooling fan operation. If there is a Class 2 communication malfunction between the BCM and the PCM. The PCM will operate the engine cooling fans independently of the BCM.

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 PCM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the engine wiring harness junction block. The ground path is provided at G101.

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

The BCM will request low speed cooling fan operation from the PCM under the following conditions:

Engine coolant temperature exceeds approximately 212°F (100°C).
When A/C is requested and the ambient temperature is more than 50°F (10°C).
A/C refrigerant pressure exceeds 190 psi (1310 kPa).
After the vehicle is shut off if the engine coolant temperature at key-off is more than 243°F (117°C) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The BCM will request high speed cooling fan operation from the PCM under the following conditions:

Engine coolant temperature reaches 221°F (105°C).
A/C refrigerant pressure exceeds 240 psi (1655 kPa).
When certain DTCs set.