The engine control module (ECM) can command the fans ON at high speed or low speed. The fan completes a series circuit at low speed and a parallel circuit at high speed.

The ECM will ground the relay control side of the low speed fan relay (relay 1) at low speed. The ECM directly supplies power to the left side cooling fan through the solenoid side of low speed relay. The right side cooling fan is connected in series to the left side fan through the de-energized series/parallel relay, so that both fans operate at low speed.

The ECM ground the relay control side of the low speed fan relay (relay 1), S/P relay and the high speed relay (relay 2) together at high speed. Applied power directly to the right side cooling fan through the solenoid of the high speed relay. By connecting the S/P relay, the left side cooling fan ground to obtain the voltage.

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 potential of the control circuit should be high, near battery voltage.

DTC P0480, P0481 are the type B DTC.

DTC P0480, P0481 are the type B DTC.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information

Scan Tool Reference

Special Tools

J 43244 Relay Puller Pliers

1. Turn the ignition switch OFF and disconnect S/P connector.
2. Connect a 30A fused jumper between the normally-open switch connection terminals R15 and R16 at the S/P fan relay connector to ensure circuit integrity of the fan ground circuit, and keep it in the proper circuit position.
3. Turn the ignition switch OFF and disconnect the affected relay.
4. Turn the ignition switch ON and connect a test lamp between the battery positive terminal and the affected relay control circuit listed below:

•	Low Speed Fan Relay Terminal R42

•	High Speed Fan Relay Terminal R22

5. Use the scan tool to command the affected relay ON and OFF. The test lamp should turn ON or OFF with the change of the commanded states.

•	Fan relay 1 commands the low speed fan relay.

•	Fan relays 2 and 3 command the high speed fan relay

⇒	If the test lamp remains illuminated at all times, test for a short to ground in the relay control loop. If the circuit tests normal, replace the ECM.

⇒	If the test lamp stays OFF all the time, test relay circuit for a short to voltage, an open or high resistance. If the circuit tests normal, replace the ECM.

6. Connect a 30 A fused jumper between the battery positive voltage terminal and the fan feed circuit terminal of the affected relay connector listed below, and verify the activation of the fan.

•	Low Speed Fan Relay Terminal R41

•	High Speed Fan Relay Terminal R21

⇒	If the fan does not activate, test the fan feed circuit for a short to ground or open/high resistance. If the circuits test normal, replace the fan.

7. Turn the ignition switch OFF, connect a 30A fused jumper between the relay solenoid feed circuit terminal and the fan feed circuit terminal of the affected relay connector listed below, and verify the activation of the fan.

•	Low Speed Fan Relay Terminal R41

•	High Speed Fan Relay Terminal R21

⇒	If the fan does not activate, test the affected relay solenoid feed 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.

8. Turn the ignition switch ON, and verify that the test lamp between the affected relay coil feed circuit terminal and ground is ON.

•	Low Speed Fan Relay Terminal R39

•	High Speed Fan Relay Terminal R19

⇒	If the test lamp is OFF, test the affected relay coil feed 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.

9. If all circuits and the ECM test normal, replace the affected relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.