97 A4 2.8, dash temp gauge reading stone cold all the time... I searched and read about the sensor to replace, but does this one sensor feed the ECU also? I would think a broken sensor would trip a CEL, wouldn't it? Heater works OK after engine is warmed up... Just wondering if ECU gets coolant temp from a different sensor than the one feeding the gauge....

 

I have a similar issue. There is only one physical sensor. Within the one, there are two different thermistors. One to drive the ECU and the other for the dash. If the sensor is in the same location on your 12v as my 30v, it is in a coolant pipe on the passenger side of the engine next to the firewall, just below the throttle body.

http://www.audiworld.com/tech/eng54.shtml

It's really not that bad to replace. I replaced mine in less than 15 min, though it did not fix the problem. I assume that since I still have the same symptoms, the thermostat must be the problem. As the ECT was easier to replace, I elected to start there.

 

He's right, that's where it is. Be careful not to break the shitty corrugated plastic tube coming out of the valve cover = $$.

 

Thanks, been there and done that with that stupid plastic breather hose, it had broken before and caused a CEL... replaced with heater hose.. I'll give the sensor a shot, seems inexpensive enough...

 

true dat. and be careful of the stupid flimsy plastic horseshoe clip thing that holds the sensor in. broke mine lolz. its a dollar or two at the stealership