Cooling Fan Always On w/LFA

The hybrid engine cooling fan system consists of two electrical cooling fans, two resistors, three engine control module (ECM) fan output control drivers, and five fan relays. The relays are arranged in a series/parallel configuration that allows the ECM to operate the fans at low, medium, or high speed depending on engine cooling requirements. The ECM controls the five relays by grounding the relay control circuits.

During low speed operation, the ECM supplies the ground path for the low fan relay control circuit. This energizes the low fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the de-energized fan control relay, through the right cooling fan in-line resistor, and through the right cooling fan. The result is a series circuit with both fans running at low speed.

During medium speed operation the ECM grounds one control circuit that energizes a bank of three relays consisting of the FAN Mid 1 relay, the fan control relay, and the FAN Mid 2 relay. When these three relays are energized the Mid 1 relay supplies battery voltage to the left cooling fan through the left cooling fan resistor. A ground path is provided for the left fan through the energized fan control relay. At the same time the Mid 2 relay is energized which applies battery voltage to the right cooling fan through the right cooling fan resistor. The result is a parallel circuit where each fan has voltage applied through a resistor which causes each fan to operate at reduced speed.

During high speed operation the ECM grounds all three relay control circuits which activates all five relays. This allows full battery voltage to be applied to the right cooling fan from the high fan relay, and full battery voltage to be applied to the left fan from the low fan relay. The left fan is grounded through the fan control relay. In this arrangement each fan has full battery voltage applied and each fan has its own ground path. The result is a parallel circuit with both fans running at high speed.

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. Verify that the following DTCs are not set: P0480, P0481, P0482.

⇒	If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Verify with a scan tool that the ECM is not commanding fan relay activation.
3. Ignition ON, verify with a scan tool that the ECM is not commanding fan activation.
4. Ignition ON, observe that the fans are not activated.

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

1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description .
2. Ignition ON, verify the scan tool hood position parameter displays Open.

⇒	If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.

3. Ignition OFF, leave the fan control relay in place while disconnecting the other relays.
4. Ignition ON, observe that the fans are not activated.

⇒	If the fans are not activated, replace the faulty relay.

⇒	If a fan is activated, test the fan voltage supply circuits for a short to voltage.

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 Always On w/o LFA

The engine control module (ECM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.

In low speed operation, the ECM applies ground to the coil side of the fan low relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the fan low relay, which is fed by the fan 1 fuse. The right fan is connected in series to the left fan through the de-energized fan control relay so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the fan low relay, the fan control relay , and the fan high relay. On the fan high relay, the energized coil closes the switch side of the relay and applies voltage directly to the right cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. At the same time, the ECM energizes fan control relay pulling the switch side over, providing a direct path to ground for the left cooling fan, which has voltage applied through the energized fan low relay. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.

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. Ignition ON, verify with a scan tool that the control module is not commanding fan activation.
3. Ignition ON, observe that the fans are not activated.

1. Ignition OFF, disconnect the fan high relay.
2. Ignition ON, observe that both fans are now OFF.

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

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