Anyone have any suggestions/tips on the sensor replacement. Mine is constantly going off even when engine is started cold. I've checked coolant temp. and it's normal so I'm assuming the sensor is bad.

 

Not sure where yours is located. On mine ('02 A6 3.0L) its under the big accordion-like air intake hose. Its a bit hard to find. It is cheap (for mine). You might need to go to the dealer to get an O-ring and U-clip (which I am told are good to replace and cost $2.00, even at the stealership). I got mine here:
http://www.rockauto.com/