Cooling Fan Inoperative

Cooling Fan Inoperative

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. 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 5 Bow Lowered Switch (CM7)

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, verify that DTC P0480 is not set.

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

2. Ignition ON, command the cooling fan from 0-100 percent with a scan tool. The cooling fan should begin to operate and the fan speed should increase with each commanded state.

Circuit/System Testing

1. Ignition OFF, disconnect the connector from the cooling fan control module.

2. Connect a test lamp between the cooling fan control module ground circuit terminal B and B+. The test lamp should illuminate.

• If the test lamp does not illuminate, test the ground circuit for open/high resistance.

3. Verify that a test lamp illuminates between the B+ circuit terminal C and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ fuse open, test or replace the cooling fan and motor assembly.

4. Ignition ON, connect a test lamp between the cooling fan speed control circuit terminal A and B+. The test lamp should not illuminate.

• If the lamp is ON, test the cooling fan speed control circuit for a short to ground. If the circuit tests normal, replace the ECM.

5. Ignition ON, command the cooling fan speed to 50 percent with a scan tool. The test lamp should illuminate and flash.

• If the test lamp does not illuminate, test the cooling fan speed control circuit for a short to voltage or for an open/high resistance. If the circuit tests normal, replace the ECM.

6. If all of the circuits test normal, replace the cooling fan control module.

Repair Instructions

Perform the after completing the diagnostic procedure.

* Fan Control Module Replacement Service and Repair

* Control Module References Control Module References