The electric cooling fans are used to cool engine coolant flowing through the radiator. They are also used to cool the refrigerant (R134a) flowing through the A/C condenser.
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 comes from a fusible link to the cooling fan relays. The fusible link is located at the battery junction block. The relays are energized when current flows from the FANS/ACTUATOR fuse through the relay coils to ground through the PCM. The PCM Output Driver Module B output 1 is used for Low Speed fan operation. PCM outputs 1 and 2 are used for high speed fan operation. The Output Driver Module outputs are monitored by the PCM. Before using the diagnostics found in this section be sure to perform the Diagnostic Circuit Check found in section 6A. If Diagnostic Trouble Codes P1651 or P1652 are present follow the appropriate diagnostic tables prior to performing diagnostics found in this section.
The PCM will complete the ground path for the low speed cooling fans ('Fan 1') relay 1 under the following conditions:
| • | When engine temperature exceeds 105°C (221°F). |
| • | When A/C is requested (ambient temperature must be above 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). |
The PCM will complete the ground paths for the high speed cooling fans ('Fan 2') relays 1, 2 and 3 under the following conditions:
| • | When engine temperature exceeds 113°C (235°F). |
| • | When A/C refrigerant pressure is greater than 275 psi (2.9 volts). |
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 Diagnostic Circuit check prior to diagnosing the engine cooling fans.
