Operation-Diesel Engine

Radiator fan operation is control by the Engine Control Module (ECM) with inputs from the temperature of the coolant, which is sensed by the coolant temperature sensor, and vehicle speed which is measured by the vehicle speed sensor. The ECM turns on the fan through either the high or low speed fan relay. The ECM provides a ground to the relay's control circuit. The fan relays are located on the back of the fan shroud.

Refer to Radiator Fan Operation Chart  for fan operation specifications. For fan circuit wiring diagrams, refer to SYSTEM WIRING DIAGRAMS article.

If the cooling fan is inoperative or a Diagnostic Trouble Code (DTC) related to fan control has been set, refer to the appropriate Engine ELECTRICAL DIAGNOSTICS article for diagnostic procedures.