Cooling Fan Always On

Cooling Fan Always On

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

Circuit/System Description

The engine control module (ECM) grounds the relay control circuit 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.

Reference Information
Schematic Reference

Engine Cooling Schematics ([1][2]Cooling System)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Cooling Fan Description and Operation (Cooling Fan)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information

Circuit/System Verification

1. If DTC P0480 is set, perform that diagnostic first.
2. Ignition ON, verify with a scan tool that the fan is commanded OFF.
3. Observe that the fan is OFF.

Circuit/System Testing

1. Disconnect the cooling fan relay. The fan should be ON.

• If the fan is OFF, replace the relay.

2. If the relay is normal and the fan is ON, test the relay controlled output circuit terminal 87 for a short to voltage.

Repair Instructions

Cooling Fan and Shroud Replacement (Service and Repair)

Repair Verification

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.