The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed 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 is affected by many different conditions and can be adjusted from 10-90 percent duty cycle (PWM). Ninety percent is considered high fan speed. When multiple cooling speed requests are received the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation the control circuit voltage will be low and near battery voltage when the fan is OFF.

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Cooling System Connector End Views

Electrical Information Reference

1. Verify that the following DTC P1482 is not set.

⇒	If the DTC is set, refer to DTC P1482 .

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

Important: Circuit/System Verification must be performed first or misdiagnosis may result.

1. Ignition OFF, disconnect the cooling fan speed control module.
2. Ignition ON, observe that the fans are not activated.

⇒	If the fan is not activated, replace the cooling fan speed control module.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.