The engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.

In low speed operation, the ECM applies ground to the coil side of the auxiliary fan relay. This energizes the coil and applies voltage directly to the auxiliary cooling fan through the switch side of the relay. The auxiliary fan is connected in series to the main cooling fan through the de-energized series/parallel control fan relay. The series circuit operates both fans at low speed.

In high speed operation, the ECM applies a ground to the coil side of the auxiliary fan relay, the control fan relay, and the main fan relay. When energized, the main fan relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the auxiliary fan relay and the control fan relay provide ignition voltage and a direct path to ground for the auxiliary cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Cooling System Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Verify that DTCs P0480, P0481, P0691, P0692, P0693 or P0694 are not set.

⇒	If any cooling system DTCs are set, repair the DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.

⇒	If the fan is commanded ON, diagnose the ECM first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

3. Ignition ON, observe that the fan is not activated.

Important: The following tests must be performed on each cooling fan relay.

1. Ignition OFF, disconnect each cooling fan relay one at a time.
2. Ignition ON, observe that the cooling fans are not activated.

⇒	If the fans are activated, test for a short to voltage in the relay controlled output circuit.

⇒	If the fans are not activated, test for a short to ground in the relay coil control circuit.

3. If all circuits test normal, test or replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Relay Replacement