Cooling Fan Always On

Cooling Fan Always On

Diagnostic Instructions

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

Circuit/System Description

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 COOL/FAN 1 relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the COOL/FAN 1 relay, which is fed by the COOL/FAN fuse. The right fan is connected in series to the left fan through the de-energized COOL/FAN SER/PAR relay so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the COOL/FAN 1 relay, the COOL/FAN SER/PAR relay , and the COOL/FAN relay. On the COOL/FAN relay, the energized coil closes the switch side of the relay and applies voltage directly to the right cooling fan through the switch side of the relay, which is fed by the COOL/FAN 2 fuse. At the same time, the ECM energizes the COOL/FAN SER/PAR relay pulling the switch side over, providing a direct path to ground for the left cooling fan, which has voltage applied through the energized COOL/FAN 1 relay. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.

Reference Information
Schematic Reference

Engine Cooling Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

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

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Circuit/System Verification

1. If DTCs P0480 or P0481 are set, perform those diagnostics first.
2. Ignition ON, verify with a scan tool that the control module is not commanding fan activation.
3. Ignition ON, observe that the fans are not activated.

Circuit/System Testing

1. Ignition OFF, disconnect the COOL/FAN 2 relay.
2. Ignition ON, observe that both fans are now OFF.

• If both fans are OFF, replace the COOL/FAN 2 relay. If either fan is still activated, remove the COOL/FAN 1 relay. If both fans are now OFF replace the COOL/FAN 1 relay. If either fan is still activated, test for a short to voltage in the fan voltage supply circuit.

Repair Verification

1. Ignition ON, verify with a scan tool that the control module is not commanding fan activation.
2. Ignition ON, observe that the fans are not activated.