The engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. 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 fan low relay. Voltage is applied directly to the left cooling fan through the switch side of the fan low relay, which is fed by the fan 1 fuse. The right fan is connected in series to the left fan through the de-energized fan control relay so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the fan low relay, the fan control relay, and the fan high relay. Voltage is applied directly to the right cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. The left cooling fan obtains voltage through the fan low relay and ground through the fan control relay.

The ECM monitors the low and high speed cooling fan relay control circuits for the following conditions:

If the ECM detects an improper voltage level on the low or high speed ECM driver circuits, then DTC P0480 or P0481 will set and the affected ECM driver will be disabled.

DTCs P0480 and P0481 are Type B DTCs.

DTCs P0480 and P0481 are Type B DTCs.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

Special Tools Required

1. Ignition ON, command the cooling fan relay 1 ON and OFF several times using the scan tool output control function. You should hear both fans turn ON and OFF. Both should run on low speed when turned ON.
2. Ignition ON, command the cooling fan relays 2 and 3 ON and OFF several times using the scan tool output control function. When turned ON, the right fan should run on high and the left fan should remain OFF.
3. Ignition ON, command the cooling fan relays 1, 2, and 3 ON and OFF several times using the scan tool output control function. When turned ON, both fans should run on high speed.

P0480

1. Ignition OFF, disconnect the cooling fan low relay from the underhood fuse block.
2. Ignition ON, verify that a test lamp illuminates between the fan low relay coil voltage supply circuit and ground.

⇒	If the test lamp does not illuminate, test the fan low relay coil voltage supply circuit for and open/high resistance.

3. Connect a test lamp between the fan low relay coil supply voltage circuit and the fan low relay coil control circuit. With a scan tool, command the fan relay 1 ON and OFF. Verify that the test lamp turns ON and OFF with each command.

⇒	If the test lamp remains illuminated with each command, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the control module.

⇒	If the test lamp does not illuminate, test the relay coil control circuit for and open or a short to voltage. If the circuit tests normal, replace the control module.

4. If the circuits test normal, replace the fan low relay.

P0481

1. Ignition OFF, disconnect the cooling fan high relay from the underhood fuse block.
2. Ignition ON, verify that a test lamp illuminates between the fan high relay coil voltage supply circuit and ground.

⇒	If the test lamp does not illuminate, test the fan high relay coil voltage supply circuit for and open/high resistance.

3. Connect a test lamp between the fan high relay coil supply voltage circuit and the fan high relay coil control circuit. With a scan tool, command the fan relays 2 and 3 ON and OFF. Verify that the test lamp turns ON and OFF with each command.

⇒

If the test lamp remains illuminated with each command, remove the fan control relay and retest. If the test lamp now turns ON and OFF with the fan control relay removed, replace the fan control relay. If the test lamp still remains illuminated when commanded ON and OFF, test the fan high relay coil control circuit for a short to ground. If the circuit tests normal, replace the control module.

⇒	If the test lamp does not illuminate, test the fan high relay coil control circuit for and open or a short to voltage. If the circuit tests normal, replace the control module.

4. If all circuits test normal, replace the fan high relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.