Cooling Fan Motors: Maximizing Efficiency and Performance

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Purpose

The Cooling Fan Motor drives the cooling fan, also called the radiator fan. This fan draws air through the radiator to dissipate heat from the engine coolant circulating through the radiator.

Location

The cooling fan motor is located behind the radiator and cooling fan, mounted in a fan assembly that includes the fan shroud.

Operation

The cooling fan is designed to operate whenever needed to maintain engine coolant temperature within a specified temperature range. The cooling fan also operates when the vehicle’s air conditioning compressor is engaged. 

In older vehicles, the signal that turns on the cooling fan motor is sent by an electrical switch that responds to coolant temperature. In modern vehicles with electronic engine management systems, the Engine Control Module or Powertrain Control Module (ECM/PCM) commands the fan motor on based upon data from the coolant temperature sensor, the air conditioner switch position and, in some vehicles, data from the vehicle speed, air conditioner refrigerant pressure, and intake air temperature sensors. 

This signal energizes a cooling fan motor relay to close the electrical circuit routing current to the cooling fan motor, operating the fan. When coolant temperature drops below a threshold level, another signal de-energizes the relay, opening the circuit to the cooling fan motor and turning the fan off. To prevent the fan from cycling between on and off, the temperature at which the fan is turned off is always lower than the temperature that activates it.

Some vehicles are equipped with two side-by-side cooling fans. In these vehicles, one or both of the coolant fans may also function as an air conditioning condenser fan, with the fans also engaged as required to maintain air conditioner efficiency. (Some vehicles are equipped with separate cooling and air conditioning condenser fans, also located side-by-side.) 

When dual cooling fans are employed, the fans either operate simultaneously – both at low or high speed – or one fan is the primary fan and the other operates when additional cooling is required or the air conditioning compressor is engaged.

Drivability Symptoms

A failed coolant fan motor will render the fan inoperative. The most common symptom of an inoperative cooling fan is higher than normal coolant temperature when the vehicle is idling or moving at low speed. 

Coolant temperature drops as vehicle speed increases, increasing airflow through the radiator.

Inspection, Test, and Diagnosis

WARNING: Electric cooling fans can activate without warning, even when the engine is not running and the ignition key is in the off position. Always keep hands away from cooling fan blades during diagnostic procedures.

Though 1996 and later automobiles and light trucks are equipped with Second Generation On-Board Diagnostics (OBD2), there are no Diagnostic Trouble Codes (DTCs) specific to cooling fan motor malfunctions. Even so, the first step in diagnosing an inoperative cooling fan is to retrieve and diagnose any stored DTCs. 

In some cases, the malfunction setting a code may prevent cooling fan operation. For example, DTCs P0480 through P0485 indicate faults in either the electrical circuit controlling cooling fan operation or the circuit supplying current to the cooling fan. DTCs P0115 through P0119 indicate malfunction of the coolant temperature sensor or its circuit. 

In addition to these “generic” codes (codes that are uniformly applicable to all OBD2 vehicles regardless of vehicle manufacturer), “enhanced” codes unique to a specific vehicle manufacturer may refine diagnostic procedures for an inoperative fan. The absence of codes allows provisionally excluding as causes those conditions which would, if present, set a DTC.

Start the engine and turn on the air conditioning. In almost all vehicles, this causes the ECM/PCM to command the cooling fan on, at least at low speed. If the fan operates, the motor itself is functioning properly. If the motor does not operate, disconnect the wiring harness connector from the fan motor and clean any corrosion from the connector terminals. 

Using jumper wires and keeping clear of the fan blades, connect the positive terminal of the fan motor connector to the positive battery terminal and then connect the ground terminal to a good ground. 

The fan motor should operate at full speed. If it does, the fan motor is good. The fault is either in the wiring or the cooling fan motor relay. If the fan motor does not operate when connected directly to battery voltage, it is defective and must be replaced.

Reprogramming

Replacement of a cooling fan motor does not require reprogramming.

Repair/Replacement

Disconnect the negative battery cable to prevent inadvertent fan activation during the service procedure. On some vehicles, cooling fan motor failure requires replacement of the entire cooling fan motor assembly as a unit. On other vehicles, once the assembly has been removed, the fan motor can be replaced separately.

Removing the cooling fan motor assembly requires removing other components, including the fascia or “sight shield” covering the top of the radiator, to clear a path for removal of the assembly. While the exact components which must be removed depend on the vehicle being serviced, normally it is not necessary to disconnect any coolant hoses. 

The fan assembly is held in place by several bolts. Once they have been removed and the wiring harness disconnected from the fan motor, the assembly can be guided out of the engine compartment.

To remove the motor from the assembly, remove the bolt holding the fan to the motor. (This bolt may unscrew in the direction opposite fan rotation.) After removing the fan, the bolts holding the motor to the assembly will be visible and can be removed to remove the fan motor. Installation is the reverse.

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