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

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 a DTCs is set, refer to DTC P0480 or P0481.

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

1. Ignition OFF, disconnect the appropriate cooling fan relay.
2. Ignition ON, verify that the cooling fan is not ON.

⇒	If the fan is ON, test for a short to voltage in the relay controlled output circuit terminal 87.

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