Operation
Power for the cooling fan motors comes from the cool fan 1 and cool fan 2 Maxi fuses®.
During low speed operation, the PCM supplies a ground path for the cool fan 1 relay through the Llow speed fans control circuit. This energizes the relay coil, closes the fan 1 relay contacts, and supplies current to the primary cooling fan. The ground path for the primary cooling fan is through the series/parallel cooling fan relay (cool fan 2 relay) and secondary cooling fan motor. The result is 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 seconds delay, the PCM supplies a ground path for the series/parallel (cool fan 2 relay) and the high speed cooling fan (cool fan #3) relays through the high speed fans control circuit. During high speed operation, both the primary and the secondary cooling fans are supplied current through their respective maxifuse and each fan has its own ground.
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 Powertrain On Board Diagnostic (OBD) 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 100°C (212°F). |
| • | When A/C is requested and ambient temperature is greater than 4°C (39°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 6 seconds. The 6 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 108°C (226°F). |
| • | When A/C refrigerant pressure is greater than 244 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.
