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Cooling Fan Always On (LF1)

Cooling Fan Always On (LF1)

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of the diagnostic category.


Circuit/System Description

The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two resistors. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.

Diagnostic Aids


• The scan tool cooling fan output control operates as follows:

- Cooling Fan Relay 1 operates the fan at a low speed

- Cooling Fan Relay 2 and 3 operates the fan at a medium speed

- Cooling Fan Relay 1, 2 and 3 operates the fan at a high speed

• When disconnecting or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the correct orientation in the fuse block. Test the mating electrical terminals for tightness.

• If the cooling fan operates at high speed when the ECM is requesting medium speed operation, test or replace the KR20E cooling fan speed control relay and X50A UBEC.


Reference Information

Schematic Reference


• Engine Cooling Schematics

• Electrical Center Identification Views


Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation (LF1) Cooling Fan Description and Operation (LAU)

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


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

2. If any cooling system DTCs are set, repair the DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

3. Ignition ON, check the scan tool Cooling Fan Relay 1 and Cooling Fan Relays 2 and 3 Command parameters. The parameters should display OFF.

4. Ignition ON, observe that the fan is not activated.


Circuit/System Testing


1. Ignition OFF, disconnect the KR20D cooling fan high speed relay.

2. Ignition ON, observe that the fan is not activated.

3. If the fan is not activated, test or replace the KR20D relay.

4. Ignition OFF, disconnect the KR20P cooling fan medium speed relay.

5. Ignition ON, observe that the fan is not activated.

6. If the fan is not activated, test or replace the KR20P relay.

7. Ignition OFF, disconnect the KR20C cooling fan low speed relay.

8. Ignition ON, observe that the fan is not activated.

9. Ignition OFF, connect a test lamp between B+ and KR20C relay terminal 86. The test lamp should not illuminate.

10. If all of the circuits test normal, test or replace the KR20C low speed cooling fan relay.


Component Testing


1. Ignition OFF, disconnect the KR20 cooling fan relay.

2. Test for 60-100 Ω between terminals 85 and 86.

3. If not within the specified range, replace the KR20 cooling fan relay.

4. Measure the resistance between the terminals listed below. The DMM should display OL.

• 30 and 86

• 30 and 87

• 30 and 85

• 85 and 87

• If less than the specified range, replace the KR20 cooling fan relay.

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

6. If greater than the specified range, replace the KR20 cooling fan relay.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)

• Front Compartment Fuse Block Replacement