Operation
The engine cooling fans receive power from separate maxifuses located in the Underhood Electrical Center. During low speed operation, the PCM supplies a ground path for the Cool Fan 1 relay through the Low Speed Fans control circuit. This energizes the relay coil, closes the Fan 1 relay contacts, and supplies current from the 40 amp maxifuse to the engine cooling fans. Engine Coolant Fan #1 grounds through the series/paralles cooling fan relay (Cool Fan 2 Relay) and Engine Coolant Fan #2. This creates a series circuit with both fans running at low speed.
To command high speed cooling fan operation, the PCM first supplies a ground path for the low speed cooling fan (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 Relay and the Cool Fan #3 relays through the High Speed Fans Control circuit. Engine Coolant Fan #1 continues to receive current from the 40 amp maxifuse. However, a 30 amp maxifuse supplies current to Engine Coolant Fan #2. Each fan receives a separate path to ground. Therefore, the fans operate at high speed.
Important: When certain Diagnostic Trouble Codes (DTCs) set, 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 completes the ground path for Cool Fan 1 relay 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 operation, the PCM delays control of the Cool Fan 2 and Cool Fan 3 relays for 3 seconds. The 3 second delay ensures that cooling fan electrical load does not exceed the capacity of the system. The PCM completes the ground paths for Cool Fan 1, Cool Fan 2 and Cool Fan 3 relays 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). |
Diagnosis
DTC P1651 should set if a problem occurs which affects the low speed fans control circuit. If the problem affects the high speed fans control circuit, 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. Therefore, diagnose any ECT DTCs before using the Electric Cooling Fan Diagnosis table. If no DTCs set and a cooling fan problem exists, use the Electric Cooling Fan Diagnosis to diagnose the PCM controlled cooling fans.
