Cooling Fan Inoperative

Cooling Fan Inoperative

Circuit/System Description

The engine control module (ECM) commands the fans ON in high speed or low speed. In low speed, the fans are configured in series. In high speed, the fans are configured in parallel.

In low speed operation, the ECM applies ground to the coil side of the low speed relay. Voltage is applied 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 series/parallel relay so that both fans 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. Voltage is applied directly to the right cooling fan through the switch side of the high speed relay. The left cooling fan obtains voltage through the low speed relay and ground through the series/parallel relay.

When the ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage of the control circuit should be high, near battery voltage. If the ECM detects that the actual voltage of the relay control circuit is different than the expected voltage, DTC P0480 or P0481 will set and the affected ECM driver will be disabled.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

^ Cooling System Component Views
^ Cooling System Connector End Views
^ Engine Control Module Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

^ Scan Tool Data List
^ Scan Tool Data Definitions
^ Scan Tool Output Controls

Circuit/System Verification

1. If DTCs P0480 or P0481 are set, then perform those diagnostics first.
2. Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that the fan turns ON and OFF with each command.

Circuit/System Testing

1. Ignition OFF, disconnect the relays.
2. Install a 30A fused jumper between the relay switch supply circuit terminal and the normally open relay switch contact circuit terminal at the series/parallel relay connector. Leave this jumper installed for the remainder of this procedure.
3. Install a 30A fused jumper at the positive terminal at the battery.
4. One at a time, connect the other end of the jumper to each fan voltage supply circuit terminal at each relay connection and verify fan activation.
- If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the fan does not activate and the circuits test normal, replace the fan.

5. Ignition ON, install a 30A fused jumper between the relay switch voltage supply circuit terminal and the fan voltage supply circuit terminal at the low speed relay connection and verify fan activation.
- If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.

6. Ignition ON, install a 30A fused jumper between the relay switch voltage supply circuit terminal and the fan voltage supply circuit terminal at the high speed relay connection and verify fan activation.
- If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.

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

Repair Instructions

^ Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
^ Cooling Fan and Shroud Replacement (L61) Cooling Fan and Shroud Replacement (LZ4, LZ9)
^ Engine Control Module Replacement

Repair Verification

Ignition ON, command each relay ON and OFF with a scan tool. Observe to verify that the fans turn ON and OFF with each command.