2004 2.5T AWD Cooling Fan Runs on High

When the engine is running, the radiator cooling fan runs full-bore. The temperature sensor seems to be fine as the temp gauge reads accurately. I can run the car with the fan unplugged as long as I'm not in the city, so I assume the thermostat is opening properly, not that it affects the fan.

This problem started a few weeks after I replaced the radiator. In the process of doing so, I damaged an o-ring in the A/C system and much of the refrigerant leaked out before I could seal it. I have yet to drain the system and replace the o-ring. I suspect the low refrigerant might cause the pressure to drop, so it shouldn't make the fan kick on, but I might be mistaken.

I checked the voltage on the fan module control wire (purple wire into fan motor) and it reads 0.7 volts to ground when the engine is running. I believe this is the proper reading when the computer wants the fan to run high, so the problem is not the fan module integrated into the fan motor assembly.

Thank you for your help

 

It was as I suspected. I replaced the o-ring and had the A/C system evacuated, then charged by a shop. Presto! Cooling fan is operating as it should! I hope this lesson saves somebody some frustration.