Cooling Fan Inoperative with V8

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. 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.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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. Feel or listen to verify that each relay turns ON and OFF with each command.

Note: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the S/P relay.
2. Ignition ON, activate the cooling fan relay 1 with the scan tool. The fan should be OFF.

⇒	If the fan is activated, test the left fan ground circuit for a short to ground.

3. Ignition OFF, disconnect the fan relays.
4. Connect a 30A fused jumper between the normally-open switch contact terminals 30 and 87 at the S/P relay connector in order to complete the fan ground circuit. Leave this jumper in place for the remainder of this procedure.
5. One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal 87 at the fan 1 and the fan 2 relay connections and verify fan activation.

⇒	If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance.

⇒	If the circuit tests normal, test the fan ground circuit for an open/high resistance.

⇒	If the circuits test normal, replace the fan.

6. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal 30 and the fan voltage supply circuit terminal 87 at the fan 1 and the fan 2 relay connections and verify fan activation.

⇒	If the fan does not activate, test the relay switch voltage supply circuit for a short to ground or high resistance.

⇒	If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.

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

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

Cooling Fan Inoperative with V6

The engine cooling fan system consists of one electrical cooling fan, a serviceable resistor module mounted in the cooling fan shroud, and three fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. The resistor module is a self-contained unit providing a specific resistance through three individual circuits. To activate the fan, the ECM applies ground to the coil side of the applicable fan relays. The cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G104.

When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the correct orientation in the fuse block. Test the mating electrical terminals for tightness.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the DTC information with a scan tool. Verify that DTC P0480, P0481, P0691, P0692, P0693 or P0694 is not set.

⇒	If any of the listed DTCs are set, Refer to DTC P0480, P0481, P0691, P0692, P0693, or P0694.

2. Ignition ON, command the fan relays ON and OFF with a scan tool. Verify that the fan operates at low, medium and high speed.

1. Ignition OFF, disconnect the harness connector at the cooling fan resistor.
2. Test for less than 5 Ω between the cooling fan motor ground circuit terminal 2 and ground.

⇒	If greater than the specified range, test the ground circuit for and open/high resistance.

3. Connect a test lamp between the cooling fan motor voltage supply circuit terminal 4 and ground. Command the FC relay 1 ON and OFF with a scan tool. The test lamp should respond to the scan tool commands.

⇒	If the test lamp remains OFF all of the time, test the voltage supply circuit for an open/high resistance or a short to ground. If the circuit tests normal, test or replace the fan relay 1.

⇒	If the test lamp remains ON all of the time, test the voltage supply circuit for a short to voltage. If the circuit tests normal, test or replace the fan relay 1.

4. Connect a test lamp between the cooling fan motor voltage supply circuit terminal 3 and ground. Command the FC relay 2 and 3 ON and OFF with a scan tool. The test lamp should respond to the scan tool commands.

⇒	If the test lamp remains OFF all of the time, test the voltage supply circuit for an open/high resistance or a short to ground. If the circuit tests normal, test or replace the fan relay 2.

⇒	If the test lamp remains ON all of the time, test the voltage supply circuit for a short to voltage. If the circuit tests normal, test or replace the fan relay 2.

5. Connect a test lamp between the cooling fan motor voltage supply circuit terminal 1 and ground. Command the FC relay 1, 2 and 3 ON and OFF with a scan tool. The test lamp should respond to the scan tool commands.

⇒	If the test lamp remains OFF all of the time, test the voltage supply circuit for an open/high resistance or a short to ground. If the circuit tests normal, test or replace the S/P fan relay.

⇒	If the test lamp remains ON all of the time, test the voltage supply circuit for a short to voltage. If the circuit tests normal, test or replace the S/P fan relay.

6. Connect the harness connector at the cooling fan resistor. Disconnect the harness connector at the cooling fan motor.
7. Connect a test lamp between the voltage supply circuit terminal 1 and the ground circuit terminal 2. Command the cooling fans ON in all 3 speeds. Verify the test lamp illuminates in all 3 speeds.

⇒	If the test does not illuminate in all 3 speeds, replace the cooling fan resistor.

8. If all circuits/connections test normal, replace the cooling fan motor.

1. Ignition OFF, disconnect the appropriate cooling fan relay.
2. Test for 200-240 Ω between terminals 85 and 86 of the relay.

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

3. Test for infinite resistance between the terminals listed below.

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Test for less than 2 Ω between terminals 30 and 87A.

⇒	If greater than the specified range, replace the relay.

5. Install a 20 A fused jumper wire between B+ and relay terminal 85. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

⇒	If greater than the specified range, replace the cooling fan relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.