Electric Cooling Fan

Operation

During low speed operation, the engine coolant fans receive power from a 30 amp maxifuse. The PCM supplies a ground path for the Cool Fan 1 relay through the Coolant Fan # 1 Relay Control circuit. This energizes the relay coil, closes the Fan 1 relay contacts, and supplies current to engine coolant fan motor # 1. The ground path for cooling fan # 1 is through the series/parallel cooling fan relay (Cool Fan 2 relay) and engine cooling fan motor # 2. The result is a series circuit with both fans running at low speed.

During high speed fan operation, engine coolant fan motor # 1 receives power from the 30 amp maxifuse. However, engine coolant fan motor # 2 receives power from the 25 amp fan # 3 fuse. The series/parallel relay coil is supplied battery positive voltage from the 20 amp PCM BAT fuse.

To command high speed cooling fan operation the PCM first supplies a ground path for the Cool Fan 1 relay through the Low Speed Fans control circuit. After a 3 second delay, the PCM supplies a ground path for the Cool Fan 2 (series/parallel) and Cool Fan 3 relays through the High Speed Fans Control circuit. During high speed operation, both engine coolant fans have their own ground path.

Important: When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may command the cooling fans to run all the time. It is important to perform the Powertrain On-Board Diagnostic System check prior to diagnosing the engine cooling fans.

The PCM will complete the ground path for cooling fan relay # 1 under any of the following conditions:

- When engine coolant temperature exceeds 106°C (223°F).

- When A/C is requested and ambient temperature is greater than 50°C (122°F).

- When A/C refrigerant pressure is greater than 190 psi (2 volts).

- When the ignition is off and engine coolant temperature is greater than 140°C (284°F).

For high speed cooling fans operation, the PCM will delay control of the Cool Fan 2 Relay and Cool Fan # 3 relay for 3 seconds. The 3 second delay ensures that the cooling fan electrical load will not exceed the capacity of the system. The PCM will complete the ground paths for cooling fan relays Cool Fan #1, Cool Fan # 2 Relay and Cool Fan # 3 under any of the following conditions:

- When engine coolant temperature exceeds 110°C (230°F).

- When A/C refrigerant pressure is greater than 240 psi (2.5 volts).

For diagnostic information see Electric Cooling Fan Diagnosis under Computers and Control Systems. Component Tests and General Diagnostics