GMC Envoy:

problems with engine fan

If the fan is not operating at the proper speed/function, a diagnostic trouble code should set.

The first thing you should do is to scan the computer for any trouble codes with a diagnostic OBD2 scanner. Repair any codes that may appear.

A scanner can test the operation of the fan circuit by commanding the relay on and off through internal test parameters.

The PCM controls the electro-viscous fan clutch engagement. The PCM regulates a 12-volt pulse width modulated signal to the cooling fan relay. The signal determines the ON time of the relay. As the commanded state of the fan clutch increases so does the ON time of the relay. This ON time directly affects the amount of time the solenoid, which is internal to the fan clutch, is energized. When the solenoid in the fan clutch is energized, it opens the spring loaded valve and allows fluid to flow from the storage chamber to the fluid coupling of the cooling fan clutch, increasing the fan speed. When the solenoid is de-energized, the spring loaded valve closes, and blocks the path of the fluid to the fluid coupling of the fan clutch, reducing fan speed.

The fan relay is in the power center under the hood. It is relay number 3. Also check fuse number 20 (10 amp) with a test light to see if it is blown.

IMPORTANT: Installation of the proper relay is critical. If an enhanced relay equipped with a diode is installed into a position requiring a standard relay equipped without a diode; excessive current will damage any components associated with the relay or its associated circuits.

Last edited by TechHelp2 (1/11/2010 10:39 AM)