The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate a fan, the ECM applies ground to the coil side of the applicable fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the relay.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Verify that DTCs P0480 and P0481 are not set.

⇒	If any cooling system DTCs are set, repair the DTC first. Refer to DTC P0480 or P0481.

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 DTC P0480 or P0481.

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