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Discussion Starter · #1 ·
Hi all, I was wondering if I could get some help diagnosing a problem I've been having. Went through a bunch of threads on multiple forums, and I've narrowed it down to either my thermostat or my coolant temp sensor. Before going and straight out asking, I did all the suggested tips, but at this point I'm stuck.

About a week and a half ago my Check Engine light came on, so I took my TT (2005, 1.8T, 225) to an auto parts store to get the code read. They said it was P2181 - Performance Malfunction in Cooling System. They cleared it for me and told me to keep an eye on it. I started my research online, checking this forum, AudiForums, and VWVortex. Somewhere I found a post saying that if its the first time, just drive on, but keep an eye on the coolant temperature gauge. I didn't see anything weird. About 4 or so days later, the CEL came back on with the same code. I got it cleared again, but this time noticed that the dash gauge goes up really slowly. At one point I even noticed that after being parked for 3 hours, it didn't start from the very bottom when I started the car. This is when I started doing more in depth research. Somewhere else on the internet I read that you can check if its the thermostat or the coolant temp gauge by checking the climate control. I did as the post suggested, and found that my AC blows freezing cold air on LO and really hot air on HI - so no help there. More research got me to the Climatronic codes. I monitored those on my way home from work (40 miles both on and off the highway) today and heres what I found (the dash gauge was pointing straight up never moving the whole time).

49C - At highway speeds (~70mph) it was fluctuating between 84 and 88deg. At medium speeds (~55mph) it was showing 92-94deg. And at the lights it was showing 97-101deg.
51C - 90deg all the way

Halfway home, my CEL came on again, so I took it to the store thinking it was another P2181, but it turned out to be different. The first place showed a P0501 and P0507. They said that the P0507 code was "PENDING" and most likely a fluke, so I asked them not to clear it. Took it to another show for a 2nd opinion and they only showed a P0501. I don't think this is related to my cooling issues, but its worth noting since this happened while I was messing around with the Climatronic codes (I also checked 17C, 28C, and 31C out of curiosity).

So what do you guys think? Thermostat? Coolant temp sensor? Both? Should I be worried about the P0501 code I got?
Let me know if you need any more info - I tried to include everything useful could think of.
(only reason I'm getting codes read at auto parts stores instead of dealers and Audi/VW shops is because they all close early in my area)

PS/offtopic - At the 2nd shop I stopped by today, I saw this beautiful 2005 TT 3.2. Gorgeous color.
 

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2001 Amulet Red 225 coupe.Owned from new as well as a Nurburg VXR & an XR3, all from new.
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Hi CrzRsn, Coolant temp seems perfect to me & thermostat controlling temp as it should. Gauge is weighted to read 90 any where between 82 & 98 ish. Fans cut-in approx 104 ish.
Sounds like coolant temperature sensor to me. Replace it using an OEM sensor. click link..
http://www.wak-tt.com/tempsensor/tempsensor.htm
Hoggy. :D
 

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Discussion Starter · #3 ·
Thanks a lot Hoggy!

I'm going to order a coolant temp sensor really soon and get this taken care of, but first I noticed some new strange (to me) behavior today.

Was driving to work today - 10 minutes after leaving home I was driving down the highway when the CEL came back on. I noticed my temp gauge was only at the 2nd tick mark (on the cold side) so I immediately switched to the 49C readout. That was showing 77-78. About 5 minutes later the gauge went up to the middle mark really quickly (~5 seconds) and the 49C readout jumped to 82-83. As I took the offramp the gauge went back DOWN to the 2nd tick mark (cold side), then back up as I merged onto another highway about a minute later - wasn't paying attention to the 49C readout on the ramp. On the 2nd highway all seemed fine and the 49C was reading 83-84 all the way to work.

Haven't had the code read yet, but I'm willing to bet its going to be a P2181 again.
Does this still sound like the temp sensor?
 

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2001 Amulet Red 225 coupe.Owned from new as well as a Nurburg VXR & an XR3, all from new.
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95,371 Posts
HI The temp sensor will be causing the fault alarm, but with the varying temp you may have an intermittent thermostat prob, but change the sensor first with an OEM one & then monitor temps using Code 49c on CC.
Hoggy. :D
 
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