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Any TT owner experiencing hesitant cold start-up problems be sure to double check your Coolant Temp Sensor regardless of color or recent replacement. As you're about to find out, green sometimes doesn't mean 'GO'.

Per the dealer service record I aquired when I bought my TT a few weeks back, it reported that my coolant temp sensor and MAF were both replaced due to a check engine light that appeared while the dealership had ownership of the vehicle. Which they no doubt did and did correctly, however after a few weeks into my ownership I was experiencing the same hesitant cold start-up problems my past two Audi's had also. Annoying? Yes. Something worth ignoring and passing off as 'standard 1.8T functionality'? No way in hell, I was finally fed up.

After studying the forums for days and reading every article regarding the coolant temp sensor issue I decided it was time to take action and investigate my issue deeper. Once I found the green coolant temp sensor and removed it (and I quickly discovered that it's easier to remove the retention tab FIRST, then remove the wire harness SECOND) I came face to face with a part that I knew was infamous for creating so many frustrated TT owners across the globe. Waiting till the next morning to perform the procedure and releasing pressure from the coolant reservoir as religiously mentioned, I only spilled out a few teaspoons worth of coolant on the bellhousing as expected. Easy clean-up, and I had a full gallon of G12 coolant waiting on the side-lines incase an unexpected catastrophy took place. As you can see from the pictures my temp sensor was infact the latest and greatest. Green in color, and current part number. Upon closer inspection, looking inside the plug/connector end it was visually obvious to me why my 'recently replaced' coolant temp sensor was causing so many problems. Look at that build-up! What in the hell is that in there, and how did it get in there? It looks like someone poured themselves a tablespoon of starbucks coffee in the connector end of the sensor, refused to rinse it out and proceed to plug it back into the wire harness!

Anyhow I replaced this 'dirty' and troublesome sensor with a brand new one I picked up from my local VW dealership (the Audi dealer was a longer drive). I also took into account what other people on the forums had mentioned and made SURE I removed the old/original 'O' Ring and replaced it with the new one I got with the new sensor. Interesting how no one previously mentioned to use pliers or some type of pinching device to easily remove the current 'O' ring, that in my case, was wedged pretty good in its original resting place. Installed the new 'O' ring on the new sensor, plugged the wire harness into the new sensor, inserted the connected sensor into the hardline, applied reasonable pressure down onto the installed sensor and proceeded to install the retention harness. Checked installed plug &amp; harness VERY carefully with a flashlight to ensure proper installation so no 'accidents' would occur during driving. Carefully poured water onto bell housing to clean off tiny coolant spillage, got into driver seat and held breath while turning ignition........Success. First cold start of the day and car didn't proceed to have it's hesitant start-up. Problem solved. And to think this whole time I thought it was a gasoline brand issue.

What's the whole point of this story and detailed write up? Simple. Don't assume just because you have the updated 'green' coolant temp sensor in your car that it can't go bad soon thereafter. If you've recently replaced your black or blue sensor with these new updated green sensors, I have just proven even the new green ones have bad batches also. It seems to be a luck of the draw for getting a good reliable sensor. I think the problem may have more to do with this coffee-like build-up/condensation that seems to appear inside the socket end of the sensor. I am 99.9% convinced that the build up ruined the connectors inside the sensor thus casing it to report inacurate/corrputed data to the ECU during a cold start-up...you know the rest of the story.

Hope this helps anyone else who might find this discovery useful. It will be interesting to see how long the new sensor will last for me before it fails also. I'm about to make a collection of these so I am send em back to Audi in a ziplock bag with a note attached that says, "I think one of your engineers needs to be fired."

 

Interesting!

 

Very good.....Guess I better hold onto that bag of 3 that I have!

 

too bad there's no way for us to tag these types of posts for ease of future retrieval...

 

Starbucks coffee anyone....?

 

i always associated the cold start problem with APR, but maybe it was just luck that it started to happen at the same time.

 

A bit of Skoal from the previous mechanic, perhaps?

 

If you've replaced this plug once and you're still having the problems (chipped or not), replace it again.....and again......and again until you find one that works. Normally I wouldn't recommend this practice with european parts due to cost, but this part isn't more than $5-7. Its even worth buying like 5 of them in one trip. I estimate 2 out of 5 should work. With those odds, it's amazing more 1.8T owners haven't gone postal yet.

 

Thanks for the details... bound to help someone in a similar situation, interesting too...

 

or have this stickied for the winter.