Operation
The Powertrain Control Module (PCM) controls the operation of the cooling fans. This is accomplished by providing a ground path for the cooling fan relay coils within the PCM. The relay contacts will close and complete the circuit between the fusible link at the battery junction block and the fan motors. Whenever there is a fan ON request both fans will be running.
Power for the fan motors is supplied through a fusible link at the battery junction block. Battery positive voltage is applied to the cooling fan relay contacts and coils. The cooling fan relays are energized when current flows through the relay coils to ground at the PCM. The cooling fan relay #1 control circuit is used for low speed cooling fan operation. The cooling fan relay #1 control circuit and the cooling fan relay #2 and #3 control circuit are both grounded for high speed fan operation. The cooling fan relay control circuits are monitored by the PCM. Before using the Electric Cooling Fans diagnostic tables be sure to perform the Powertrain On-Board Diagnostic System Check. If diagnostic trouble codes P1651 or P1652 are present, use the appropriate DTC diagnostic tables prior to performing Electric Cooling Fans diagnostics.
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 105°C (221°F). |
| • | When A/C is requested and ambient temperature is greater than 9°C (48°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 (140°F). |
For high speed cooling fans operation, the PCM will delay control of the cooling fan #2 and #3 relays 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 #1, #2, and #3 under any of the following conditions:
| • | When engine coolant temperature exceeds 113°C (235°F). |
| • | When A/C refrigerant pressure is greater than 275 psi (2.9 volts). |
Diagnosis
If a problem that involves the low speed cooling fan relay control circuit (cooling fan relay #1 control) exists, DTC P1651 should set. If the problem affects the high speed cooling fan relay control circuit (cooling fan relay #2 and #3 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.
