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Cooling Fan Always On (LLU)

Cooling Fan Always On (LLU)

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 each diagnostic category.


Circuit/System Description

The engine cooling fan system is composed of one fan, 5 relays, the engine control module (ECM), and the associated wiring. The fan assembly includes two resistors, which enable the fan to operate at 3 speeds.

In low speed operation, the ECM provides ground from ECM terminal X2 44. The Cooling Fan Relay activates and provides ground to the coils of the Cooling Fan Medium Speed 2 Relay and the Cooling Fan Speed Control Relay. The Cooling Fan Speed Control Relay activates and provides power to the coil of the Cooling Fan High Speed Relay. The cooling fan high speed relay remains inactive because ECM terminal X2 12 is not grounded. The Cooling Fan Medium Speed 2 Relay provides power to the cooling fan motor through cooling fan terminal 2 and the internal fan resistor.

In medium speed operation, the ECM provides ground to ECM terminal X2 12. The Cooling Fan High Speed Relay remains inactive because power is not provided to the coil from the Cooling Fan Speed Control Relay. The Cooling Fan Medium Speed 1 Relay activates and provides power to the cooling fan motor through cooling fan terminal 3 and the internal fan resistor.

In high speed operation, the ECM provides ground to ECM terminals X2 12 and X2 44. As previously described, power is now provided to both cooling fan terminals 2 and 3. In addition, power and ground are now provided to the coil of the Cooling Fan High Speed Relay. The Cooling Fan High Speed Relay activates and provides power to the cooling fan motor through cooling fan terminal 4.

Reference Information

Schematic Reference


• Engine Cooling Schematics

• Electrical Center Identification Views


Connector End View Reference

Component Connector End Views

Description and Operation

Cooling System Description and Operation

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. Verify that DTCs P0480 00, or P0481 00 are not set.

2. If a DTC is set, refer to DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LLU) DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LBW, LAU) for further diagnosis.

3. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.


Circuit/System Testing

Note

You must perform the circuit/system verification before proceeding with circuit/system testing.



1. Ignition OFF, disconnect the KR20A Cooling Fan Medium Speed 1 Relay, and KR20B Cooling Fan Medium Speed 2 Relay, and KR20D Cooling Fan High Speed Relay, and KR20F Cooling Fan Relay relays.

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

3. If the fan is not activated, then replace the faulty KR20A Cooling Fan Medium Speed 1 Relay, or KR20B Cooling Fan Medium Speed 2 Relay, or KR20D Cooling Fan High Speed Relay, or KR20F Cooling Fan Relay.

4. If the fan is activated, then test the fan voltage supply circuits for a short to voltage.


Repair Verification


1. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.

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