I was told by an Audi Mechanic witch lives in my neighborhood and he says the j151 is a relay that controls or works the indash temp gauge and they go faulty on the TT
He sees that relay go bad quite often
So I'm thinking of changing mine and see if that works. I asked why then the vag-com does not give you a code..he had no answer..I guess it relays the signal from the ecu to the relay to the indash gauge..

 

Update on the dancing temp. gauge mystery:

I was setting the code to 46, not 49:-( do disregard my comments above.

Now that I have observed it on 49, I can see the temp ranges from about 95-102. If I am sitting still, then rev my engine (when it's sitting at 102) the temp comes down within a minute or so, but then begins climbing again. When I am on highway, it runs about 98.
I was reading on another forum about a problem similar to mine where the culprit was sludge.
Here's the link: The Audi TT Forum :: View topic - Overheating mystery solved:TT1.8 Owners beware

Any comments? Is a fluctuation between 95 and 103 fine, or should I be worried about sludge or some other problem?

 

Well sludge does cause some heating issues as well as other issues..
I have a catch can well running to the ground, so no Hockey puck for me so to speak..

 

98 on the highway should be okay. It should be expected to go up to 102 at idle, but try turning on the a/c when at idle and see if the cooling fans bring it back down under 100. It doesn't look like to me that you're reallly having a problem. When I had temp troubles, it turned out to be the thermostat. Occam's Razor: the simplest explanation tends to be right.

 

I have a 2000 audi tt, have tried the temperature trick on the panel and the car warms up from 80 c and then starts fluctuating between 90c and 98c when driving, but the temp gauge is a click away from the hot..the shop said it might be the water pump. so i figure ill change the timing belt as well if thats the case. please any other suggestions that might help before i go and spend the grand on getting the pump and belt changed.. thank you.

 

Hello Fireman et al., I'm sure you all have been on the edge of your seats about what was causing my little TT to overheat. It was a bad thermostat.

The therm needle now sits dead center, and never moves.
The temp trick now tells me my little -pain in the butt- runs between 90c.-93c.

"Occam's Razor: the simplest explanation tends to be right."

Now.. what to do about the remote key? It wont lock my drivers door., nor can I lock the car from the inside with the little button on the console!