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 cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is affected by many different conditions and can be adjusted from 10-90 percent duty cycle (PWM). Ninety percent is considered high fan speed. When multiple cooling speed requests are received the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation the control circuit voltage will be low and near battery voltage when the fan is OFF.

Reference Information
Schematic Reference

Engine Cooling Schematics ([1][2]Cooling System)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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)

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify that the DTC P0480 is not set.

• If the DTC is set, refer to DTC P0480 (P0480).

2. Ignition ON, observe the scan tool Cooling Fan Command parameter. The parameter should display 0 %.
3. Ignition ON, observe that the engine cooling fan is not operating.

Circuit/System Testing

1. Ignition OFF, disconnect the cooling fan speed control module.
2. Ignition ON, observe that the fans are not activated.

• If the fan is not activated, replace the cooling fan speed control module.
• If the fan continues to operate, test the cooling fan voltage supply circuit for a short to voltage.

Repair Instructions

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

* Fan Control Module Replacement (Service and Repair)
* Control Module References (Programming and Relearning)