One Cooling Fan-3 Relays

The engine cooling fan system consists of one electrical cooling fan, two resistors, and three fan relays. The relays are arranged in a configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. These speeds are obtained by three separate circuits within the cooling fan. Each circuit contains a unique resistance value. The cooling fan and fan relays receive battery positive voltage from the underhood fuse block. The ECM controls the 3 relays by grounding the relay control circuit.

Two Cooling Fans-3 Relays

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, which is relay 1. 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, which is relay 1, the series/parallel relay, and the high speed relay, which is relay 2. 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.

A vehicle equipped with the trailer package option will get 2 puller and 2 pusher electric fans. During low speed operation, all 4 electric fans will operate at low speed. During high speed operation, all 4 electric fans will operate at high speed.

P0480

The ECM detects an open circuit in the low speed cooling fan relay control circuit.

P0481

DTCs P0480 and P0481 are Type B DTCs.

DTCs P0480 and P0481 are Type B DTCs.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 43244 Relay Puller Pliers

Verify the cooling fan operation using the scan tool commands listed below:

One Fan System

Two Fan System

1. Ignition OFF, disconnect the 3 cooling fan relays listed below:

•	Lo fan SPD relay

•	HI fan SPD relay

•	Fan S/P relay

2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 85 of each relay and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

3. Verify that a test lamp does not illuminate between the ignition circuit terminal 85 and the control circuit terminal 86 of each relay.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM.

4. Remove the test lamp.
5. Ignition ON, command the affected relay ON using a scan tool. Verify the affected scan tool FC Relay Control Ckt. Short Volts Test Status parameter is OK.

•	For the Lo Fan SPD relay, use the scan tool Fan Relay 1 command.

•	For the HI Fan SPD and Fan S/P relays, use the scan tool Relay 2 and 3 command.

⇒	If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM

6. Install a 3A fused jumper wire between the control circuit terminal 86 and the ignition circuit terminal 85. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status parameter is Fault.

⇒	If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.