Cooling Fan Always On Except LAT

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 the auxiliary fan relay 12. 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, which is fan control relay 15, 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 fan relay, the series/parallel relay, and the high speed fan relay, which is the main fan relay 16. Voltage is applied directly to the right cooling fan through the switch side of the high speed fan relay. The left cooling fan obtains voltage through the low speed fan 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.

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.

⇒	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, leave the series/parallel relay, which is fan control relay 15, in place while disconnecting the other relays.
2. 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 LAT

The engine control module (ECM) grounds the low speed relay, which is the AUX fan relay, and the high speed relay, which is the main fan 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.

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, then 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 fan is not activated.

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

1. Ignition OFF, disconnect the relays.
2. Ignition ON, observe that the fan is not activated.

⇒	If the fan is not activated, replace the faulty relay.

⇒	If the 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.