Cooling Fan Always On

Cooling Fan Always On

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 cooling-left high speed relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the relay. The left fan is connected in series to the right cooling fan through the de-energized speed control relay. The series circuit operates both fans at low speed.

In high speed operation, the ECM applies a ground to the coil side of the cooling-left high speed relay, the speed control relay, and the cooling fan-right high speed relay. When energized, the right high speed relay applies voltage directly to the right cooling fan through the switch side of the relay. Simultaneously, the left high speed relay and the speed control relay provide ignition voltage and a direct path to ground for the left cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.

Reference Information

Schematic Reference

Engine Cooling Schematics [1][2]Cooling System

Connector End View Reference

* Component Connector End Views A/C Compressor Clutch

* Electrical Center Identification Views Fuse Block - Underhood Label

Description and Operation

Cooling Fan Description and Operation Cooling Fan

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 DTCs P0480, P0481, P0691, P0692, P0693 and P0694 are not set.

• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

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

3. Ignition ON, observe that the fans are not activated.

Circuit/System Testing

1. Ignition OFF, disconnect the cooling-left high speed relay.

2. Ignition ON, observe that both fans are OFF.

• If both fans are OFF, test or replace the cooling fan -left high speed relay.

• If both fans continue to operate, test the left high speed relay controlled output circuit for a short to voltage.

• If the right fan is activated, perform the next test.

3. Ignition OFF, disconnect the cooling fan-right high speed relay.

4. Ignition ON, observe that the right fan is OFF.

• If the right fan is activated, test the right high speed relay controlled output circuit for a short to voltage.

5. If the circuits test normal, test or replace the cooling fan-right high speed relay.

Component Testing

1. Ignition OFF, disconnect the cooling fan relay.

2. Test for 200-240 ohms between terminals 85 and 86.

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

3. 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 relay.

4. Test for less than 2 ohms between 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 12 volts. Install a jumper wire between 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.

* Underhood Electrical Center or Junction Block Replacement Underhood Electrical Center or Junction Block Replacement

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