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 close and complete the circuit between the fusible link at the battery junction block and the fan motors. Whenever the fans are commanded on both fans run.
Power for the fan motors is supplied through the cooling fan fuse in the RH Maxi fuse block. The cooling fan relays are energized when current flows from the Cooling Fan fuse in the instrument panel (IP) fuse block through the relay coils, to ground through the PCM. The cooling fan 1 control circuit is used for low speed cooling fan operation. The cooling fan 1 control circuit and the cooling fan 2 control circuit are both grounded for high speed fan operation. The cooling fan 1 and cooling fan 2 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 DTC P1651 or DTC P1652 are present, use the appropriate DTC tables prior to performing the Electric Cooling Fans diagnostics.
The PCM completes the ground path for the low speed cooling fan relay under any of the following conditions:
| • | When the ECT exceeds 106°C (223°F), or exceeds 180°C (176°F) with low coolant. |
| • | When the A/C refrigerant pressure is more than 1372 Kpa (190 psi). |
| • | At key-off, for 3 minutes, if the ECT exceeds 118°C (244°F). |
For high speed cooling fan operation, the PCM delays control of the series/parallel and high speed cooling fan relays for 6 seconds. The 6 second delay ensures that the cooling fan electrical load does not exceed the capacity of the system. The PCM completes the ground paths for the low speed, the series/parallel, and the high speed cooling fan relays under any of the following conditions:
| • | When the ECT exceeds 112°C (234°F), or exceeds 100°C (212°F) with low coolant. |
| • | When A/C refrigerant pressure is more than 1632 Kpa (237 psi). |
Important:: When certain powertrain diagnostic trouble codes 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 before diagnosing the engine cooling fans.
