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 control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.

In low speed operation, the ECM applies ground to the coil side of the low speed fan relay, which is cool/fan 1 relay 28. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low speed relay. The right fan is connected in series to the left fan through the de-energized cool series/parallel relay, which is COOL SER/PAR relay 29 so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed relay, the series/parallel relay, and the high speed relay, which is cool/fan 2 relay 30. On the cool/fan 2 relay, the energized coil closes the switch side of the relay and applies voltage directly to the right cooling fan through the switch side of the relay. At the same time, the ECM energizes fan control relay pulling the switch side over, providing a direct path to ground for the left cooling fan. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.

Diagnostic Aids

The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.

Reference Information
Schematic Reference

Engine Cooling Schematics [1][2]Cooling System
Description and Operation

Cooling Fan Description and Operation Cooling Fan
Connector End View Reference

Component Connector End Views Connector End Views By Name
Electrical Information Reference

* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Programming and Relearning for scan tool information

Circuit/System Verification

1. Verify that the following DTCs are not set: P0480 or P0481.

• If either of the DTCs is set, repair the DTC first.

2. Verify cooling fan operation using the scan tool commands listed below:

* Fan Relay 1 ON-Both fans run at low speed.
* Fan Relays 2 and 3 ON-The right fan runs at high speed, the left fan is OFF.
* Fan Relays 1, 2 and 3 ON-Both fans run at high speed.

Circuit/System Testing

Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the series/parallel relay, which is cool SER/PAR fan relay.
2. Ignition ON, activate the cooling fan relay 1 with a scan tool. The fan should be OFF.

• If the fan is activated, test the left fan ground circuit for a short to ground.

3. Ignition OFF, disconnect the remaining fan relays.
4. Connect a 30A fused jumper between the normally-open switch contact terminals at the cool series/parallel relay connector in order to complete the left fan ground circuit. Leave this jumper in place for the remainder of this procedure.
5. One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal at each relay connection and verify the appropriate fan activation.

• If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance. If the circuit tests normal, test the fan ground circuit for open/high resistance. If the circuits test normal, replace the fan.

6. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 at the low speed relay, which is COOL/FAN 1 relay and then the high speed relay, which is COOL/FAN 2 relay connections and verify the appropriate fan activation.

• If the appropriate fan does not activate, test the relay switch voltage supply circuit for a short to ground or high resistance.
• If the circuit tests normal and the fuse is open, test all connected components and replace as necessary.

7. If the circuits and fans test normal, replace the relay.

Repair Instructions

* Underhood Electrical Center or Junction Block Replacement Underhood Electrical Center or Junction Block Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Cooling Fan and Shroud Replacement Service and Repair
* Control Module References Programming and Relearning for replacement, setup, and programming

Repair Verification

Ignition ON, command the fan relay ON and OFF with a scan tool. Observe to verify that the appropriate fan turns ON and OFF with each command.