Cooling Fan Always On

Cooling Fan Always On

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit/System Description

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.

Reference Information
Schematic Reference

Engine Cooling Schematics (Diagrams)
Description and Operation

Cooling System Description and Operation (Cooling System)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

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

• If a DTCs is set, refer to DTC P0480 or P0481 (w/single fan) (P0480).

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.

Circuit/System Testing

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.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Relay Replacement (Within an Electrical Center) (Service and Repair)