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 to 84 percent duty cycle (PWM). A duty cycle of 84 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.

The ECM has the capability of providing command to the fan relays even while a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded on by the ECM.

Schematic Reference

Engine Cooling Schematics

Description and Operation

Cooling Fan Description and Operation

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the cooling fan ON and OFF with a scan tool. Observe that the cooling fan turns ON and OFF with each command.

1. Ignition OFF, disconnect the cooling fan control module.
2. Connect a jumper wire between the fan ground circuit terminal and ground.
3. Connect a 30A fused jumper wire between the positive terminal at the battery and the fan voltage supply circuit terminal 4 and verify fan activation.

⇒	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 did not activate and the circuits test normal, replace the fan.

4. Ignition ON, connect the 30A fused jumper wire between the fan control module voltage supply circuit terminal 3 and the fan voltage supply circuit terminal 4 and verify fan activation.

⇒	If the fan does not activate, test the fan control module 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.

5. If the fan and all circuits test normal, replace the fan control module.

Cooling Fan and Shroud Replacement

Ignition ON, command the fan relay ON and OFF with a scan tool. Observe that the fan turns ON and OFF with each command.