Cooling Fan Always On 2.0

The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed can be adjusted from 10 percent to 90 percent duty cycle. 90-94 percent is considered high speed fan.

The ECM monitors the voltage on the cooling fan speed control circuit driver output. Voltage is near B+ when the driver is OFF, and near ground when the driver is ON. If the difference between the actual and expected voltage exceeds a calibrated value, 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, P0691, or P0692 are set, perform that diagnostic 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.

⇒	If the fan is activated, replace the cooling fan assembly.

Perform the Cooling Fan and Shroud Replacement after completing the diagnostic procedure.

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 2.4

The engine control module (ECM) grounds the low speed relay, which is relay 1, and the high speed relay, which is relay 2, 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, command each relay ON and OFF with a scan tool. Observe to verify that the fan turns ON and OFF with each command.

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

1. Ignition OFF, disconnect the affected relay.
2. Ignition OFF, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal and verify fan activation.

•	Cooling Fan Relay 1 = Terminal 87

•	Cooling Fan Relay 2 = Terminal 30

⇒	If the fan does not activate, test the fan voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the fan does not activate and the circuits test normal, replace the fan.

3. Ignition ON, connect a 30A fused jumper from the relay switch voltage supply circuit terminal to the fan voltage supply circuit terminal and verify fan activation.

For the Relay Switch Voltage Supply Circuit

•	Cooling Fan Relay 1 = Terminal 30

•	Cooling Fan Relay 2 = Terminal 87

For the Fan Voltage Supply Circuit

•	Cooling Fan Relay 1 = Terminal 87

•	Cooling Fan Relay 2 = Terminal 30

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

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

4. If the fan and all circuits test normal, replace the faulty relay.

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.