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:

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: