Cooling Fan Inoperative LAT

The engine control module (ECM) grounds the fan main relay and the fan main relay control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON, the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the ECM detects that the actual state of the control circuit does not match the expected state, a DTC will set.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

1. If DTCs P0480 or P0481 are set, perform those diagnostics first.
2. Verify cooling fan operation using the scan tool commands listed below:

•	Fan Relay 1 ON and Fan Relay 2 OFF--Fan runs at high speed.

•	Fan Relay 1 OFF and Fan Relay 2 ON--Fan runs at low speed.

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

1. Ignition OFF, disconnect the relays.
2. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground at each relay connector.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test the control circuit terminal 87 for a short to ground.

3. One at a time, connect a 30A fused jumper between terminal 30 and terminal 87 at each relay connection and verify fan activation.

⇒	If the fan does not activate, test the control circuit terminal for an open/high resistance. If the circuit tests normal, test the fan ground circuit terminal 1 for an open/high resistance. If the circuits test normal, replace the fan.

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

Cooling Fan and Shroud Replacement

1. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
2. Ignition ON, observe that the fan is not activated.

Cooling Fan Inoperative LE5

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 fan relay. Voltage is applied directly to the left cooling fan through the switch side of fan AUX relay 3. The right fan is connected in series to the left fan through the de-energized FAN CTRL relay so that both fans operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of fan AUX relay, FAN CTRL relay, and fan main relay. Voltage is applied directly to the right cooling fan through the switch side of fan main relay. The left cooling fan obtains voltage through fan AUX relay and ground through FAN CTRL relay 2.

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.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

1. Verify that the following DTCs are not set: P0480 or P0481.

⇒	If any of the DTCs are set, repair the DTC first.

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

•	Fan Relay 3 ON--Both fans run at low speed.

•	Fan Relays 1 and 2 ON--The main fan runs at high speed, the AUX fan is OFF.

•	Fan Relays 1, 2, and 3 ON--Both fans run at high speed.

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

1. Ignition OFF, disconnect FAN CTRL relay.
2. Ignition ON, activate the fan relay 1 with a scan tool. The fan should be OFF.

⇒	If the fan is activated, test the left fan ground circuit terminal 1 for a short to ground.

3. Ignition OFF, disconnect the remaining fan relays.
4. Connect a 30A fused jumper between the normally-open switch contact terminals 30 and 87 at FAN CTRL relay connector in order to complete the left 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 each relay connection listed below and verify the appropriate fan activation:

•	FAN AUX Relay

•	Fan Main Relay

⇒	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 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 fan relay connections listed below and verify the appropriate fan activation:

•	FAN AUX Relay

•	Fan Main Relay

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

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

Cooling Fan and Shroud Replacement

1. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
2. Ignition ON, observe that the fan is not activated.