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 more than 50°C (122°F). |
| • | When A/C refrigerant pressure is more than 190 psi (2 volts). |
| • | When the ignition is off and engine coolant temperature is more 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 more than 240 psi (2.5 volts). |
Diagnosis
If a problem that involves the low speed cooling fan relay control circuit (cooling fan #1 relay control) exists, DTC P1651 should set. If the problem affects the high speed cooling fan relay control circuit (Cool Fan #2 and Cool Fan #3 Relay control), DTC P1652 should set. A problem with the ECT sensor should set DTC P0117, P0118, P1114, or P1115. Any of these DTCs will affect cooling fan operation and should be diagnosed before using the Electric Cooling Fan Diagnosis table. The Electric Cooling Fan Diagnosis table should be used to diagnose the PCM controlled cooling fans only if no DTC is set.
