Cooling Fan Inoperative (w/Single Fan)

Cooling Fan Inoperative (w/single fan)

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 operation, the ECM supplies ground to the coil side of the low speed fan relay. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the low relay. The fan is connected in series to the cooling fan resistor causing the fan to operate at low speed.

In high speed operation, the ECM supplies a ground to the coil side of the fan high or fan control relay. When energized, the fan high or control relay supplies voltage directly to the cooling fan through the switch side of the relay. Because the low speed fan relay is de-energized the cooling fan receives full voltage and operates at high speed.

Reference Information
Schematic Reference

Engine Cooling Schematics (Diagrams)
Description and Operation

Cooling System Description and Operation (Cooling System)
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 (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Verify that DTCs P0480 and P0481 are not set.

• If a DTC is set, refer to DTC P0480 or P0481 (w/single fan) (P0480).

2. Ignition ON, command the appropriate fan relay ON and OFF with a scan tool. Verify that the fan turns ON and OFF when changing between the commanded states.

Circuit/System Testing

1. Ignition OFF, disconnect the cooling fan relays.

Note: The following test must be performed on both fan relay circuits.

2. Ignition ON, verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the relay.

3. Connect a 20 A fused jumper between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87 of the fan low relay. Verify the fan is activated.

• If the fan does not activate, test the following conditions and repair as necessary.

* Open cooling fan resistor
* Relay controlled output circuit for a short to ground or an open/high resistance
* Fan ground circuit for an open/high resistance
* Cooling Fan

4. Connect a 30 A fused jumper between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87 of the fan high or fan control relay. Verify the fan is activated.

• If the fan does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance.

5. If all circuits test normal, test or replace the appropriate relay.

Component Testing

1. Ignition OFF, disconnect the cooling fan relay.
2. Test for 70-110 ohm between terminals 85 and 86.

• If the resistance is 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. Install a 20 A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohm 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.

* Relay Replacement (Within an Electrical Center) (Service and Repair)
* Engine Coolant Fan Replacement (Service and Repair)