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 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 (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
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. Verify that the following DTC P1482 is not set.

• If the DTC is set, refer to DTC P1482 (P1482) .

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



Circuit/System Testing

Important: Circuit/System Verification must be performed first or misdiagnosis may result.



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 is activated, test the fan voltage supply circuit for a short to voltage.




Repair Instructions

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


Cooling Fan Control Module Replacement (Service and Repair)