I have a 2003 VW Jetta GLS 2.0L automatic, and my check engine indicator light won't go out (cleared codes...disconnected battery, etc.), and I continue to get this annoying code relating to my ECT sensor, which I have replaced, at least the one located atop of the engine on the driver's side (was black, but replacement is green), thus allowing my cluster's temperature gauge to now work (did not before). The dealer is telling me that if I still get this code that it's probably the thermostat that I need to replace next, and if the problem persists, I should consider replacing my water pump. I was not born yesterday, and was fixing my own cars most likely well before these guys were even a twinkle in their dad's eye. At first, they explained that it was an "electronic thermostat" problem (but I caught them lying to me). I originally thought, "O.K., maybe with all of the computer controls these days, this might be the case now". So I look for it (I finally found it - attached to the end of the lower radiator hose at the block, behind and just below the alternator), but with no wires attached to it. As a matter of fact, the housing for it looked oddly like the ones I've seen all my life (of 50 yrs.), so I googled this so-called "electronic thermostat", and to my surprise, I found that the thermostat for my Jetta is just the ordinary mechanical type, not electronic at all!!!! My car does not overheat, and it does not take too much time either to warm itself up, and all fans work great too, and the heat is great, so the thermostat is working just fine. And if this is O.K., unless there is a flow sensor I don't know about somewhere, my water pump must be working just fine as well. I called the dealer again yesterday and asked them about another sensor I found, attached to the lower part of the radiator (driver's side), and was told that this was the sensor the engine computer actually uses to get coolant temperature to the computer, so my question now is: is this the sensor I should replace next? They say this sensor rarely goes out, but it can't be the thermostat NOR the water pump causing my problems now, because they are both working just fine. Hmmmm!! Has anyone else had this problem? I just keep getting the "maybe it's this, or perhaps it's that" kind of answers from the so-called "experts" at the dealership (electrornic thermostat, MY %@@")!!! I think the dealership is hoping I'll be gullible. My old 1998 Jetta 2.0L I sold to a friend, and the car at that time had > than 130,000 miles, and up to that time I had virtually NO problems with it at all. It was the best car I've ever had. So why is this car giving me SO MUCH GRIEF?

 

Hello brother,
Did you fix the problem? I have had the same problem for more than a year and there is no way I am going to take it to the dealer. They charged me $1300 for an alternator so there is no way!!!! Please let me know what the issue was. I have the same problem you had.
Thanks

 

I was pulled over for my invalid inspection sticker and finally had to go to the dealer. They replaced my thermostat and this cleared the bad codes. It's funny though that up till now, my engine never indicated more than 190 degs., no matter what. However, several times this summer, usually while sitting in traffic, my A/C turned off, and my temp. indicator showed over 212 degs. Anyway. the mechanic explained to me that the engine computer takes in several variables such as outside air temperature, coolant temperature, cylinder head temperature, etc., and then calculates how much time the thermostat should take to open up. This calculation determines how well the thermostat is functioning and aids in fuel/air mixture control. Seems to me it would be easier to just attach a flow sensor to the output side of the thermostat instead of going to all that trouble. Anyway, it cost me roughly $200 to fix the problem, and the check lamp now stays extinguished. They did replace the thermostat, as well as my catalytic converter (was bad and replaced under warranty recall) so try it and hope your lamp goes out too. Get the thermostat from VW - don't trust Autozone for this. If in fact all this computing actually takes place, use a factory part. Anyway, hope this helps. Good Luck.