volkswagen 2006 jetta tdi engine/radiator cooling fan running excessivly

Sounds like your coolant temp sensor may be bad. What it does is it kinda tells the fan when not to run so that when it goes bad the fan will always run. Kind of a defense mech so your engine won't overheat when the sensor is bad. I think the part is less than $20 but you may need to flush the coolant system to replace it. The sensor is usually located in the lower radiator hose. Not totally sure where in the tdi but vw is pretty consistent.