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) 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 low speed fan relays, which is COOL/FAN 1 relay 28. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized series/parallel relay, which is COOL/FAN SER/PAR relay 29 so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed relay, the series/parallel relay, and the high speed fan relay, which is COOL/FAN 2 relay 30. On the high speed 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. At the same time, the ECM energizes the series/parallel relay pulling the switch side over, providing a direct path to ground for the left cooling fan, which has voltage applied through the energized low speed 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 (Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

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

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Wiring Repairs (Wiring Repairs)

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 high speed fan relay, which is COOL/FAN 2 relay 30.
2. Ignition ON, observe that both fans are now OFF.

• If both fans are OFF, replace the high speed relay. If either fan is still activated, remove the low speed fan relay, which is COOL/FAN 1 relay 28. If both fans are now OFF, replace the low speed relay. If either fan is still activated, test for a short to voltage in the fan voltage supply circuit.

Repair Instructions

* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Relay Replacement (Relay Replacement (Within an Electrical Center))
* Cooling Fan and Shroud Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming

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.