Cooling Fan Always On 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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. If DTCs P0480 or P0481 are set, perform those diagnostics first.
2. Ignition ON, verify with a scan tool that the control module is not commanding fan activation.
3. Ignition ON, observe that the fan is not activated.

1. Ignition ON, disconnect the fan AUX relay. Observe that the fan is ON.

⇒	If OFF, replace the relay.

2. Disconnect the fan main relay. Observe that the fan is ON.

⇒	If OFF, replace the relay.

3. Test the relay control circuit terminal 87 for a short to voltage:

Cooling Fan and Shroud Replacement

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 Always On 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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. If DTC P0480 or P0481 are set, perform those diagnostics first.
2. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
3. Ignition ON, observe that the fans are not activated.

1. Ignition OFF, disconnect FAN AUX relay.
2. Ignition ON, observe that both fans are now OFF.

⇒	If both fans are OFF, replace FAN AUX relay. If either fan is still activated, remove fan main relay. If both fans are now OFF, replace fan main relay. If either fan is still activated, test for a short to voltage in the fan voltage supply circuit.

Cooling Fan and Shroud Replacement

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.