Cooling Fan Always On (LUV LUW)

Cooling Fan Always On (LUV LUW)

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 provide an overview of each diagnostic category.

Circuit/System Description

The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate a fan, the ECM applies ground to the coil side of the applicable fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the relay.

Reference Information

Schematic Reference

Engine Cooling Schematics [1][2]Cooling System

Connector End View Reference

Component Connector End Views Fuel Pump and Level Sensor Assembly

Description and Operation

Cooling System Description and Operation Description and Operation

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

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0480 or P0481 are not set.

• If any of the above DTCs are set, refer toA L L Diagnostic Trouble Codes ( DTC )

2. Command the cooling fan relay 1 ON and OFF with a scan tool. The cooling fan should operate on low speed when commanded ON, and turn OFF when commanded OFF.

• If less than the specified value, test the control circuit for a short to ground.

3. Command the cooling fan relay 2 ON and OFF with a scan tool. The cooling fan should operate on medium speed when commanded ON, and turn OFF when commanded OFF.

Circuit/System Testing

1. Ignition OFF, disconnect the cooling fan relays.

2. Ignition ON, verify that the cooling fans are not operating.

• If a fan is operating, test the appropriate relay controlled output circuit for a short to voltage.

3. If all circuits test normal, test or replace the cooling fan relay.

Component Testing

Static Test

1. Ignition OFF, disconnect the cooling fan relay.

2. Test for 70-110 ohms between terminals 85 and 86.

• If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If not the specified range, replace the relay.

4. Test for less than 2 ohms between the relay terminals 30 and 87A.

• If greater than the specified range, replace the relay.

5. Install a 20 A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between the relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

• If greater than the specified range, replace the relay.

Repair Instructions

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