I have the same exact issue with two same year, make and model
PD TDI's. One silver, one dk blue. One stick, one auto.
On a cold morning light goes on, and you can drive just a block or so - turn the car off then back on - and the light will go off and remain off.
The indicator is positively correlated to the temperature. Colder days cause an issue, warmer days do not. And it is perfectly consistent, on the coldest days you will always find the light goes on.
With one vehicle I added 1 cup of water even though it appeared that the coolant level was perfect. The light went out and never came back on. Problem solved.
With the other car I have done nothing yet and the light still comes on when cold out. It does seem the dividing line for triggering it is just below freezing, but low twenties and below will always find it triggered.
Interestingly on one of the vehicles the problem began the day after Jasontdi had installed an inline 1500w coolant heater. There were no leaks and the coolant was full, but I had initially thought it was related. This occurred at the start of it's third winter. The second vehicle did not have any issue until this year, its fourth winter (This is also just after Jas, did the 100k timing service on it.
) . Here is my original post on the issue:
http://forums.tdiclub.com/showthread.php?t=195846&highlight=coolant
My guess is that adding even just a few drops of water to the reservoir finds just enough slightly less mucked up wire to complete the circuit and send the
full signal out to the light. There's probably a better cleaning aid for the sensor strip than steel wool though ...