Help? Ambient temp sensor wrong, leads to engine cooling fan on 24/7

[Kai AndersFinn]

Greetings all,
I come to you with a dilemma that needs solving, as I've got my GTI ready to sell.
In May of 2017 I started the car one day and the ambient temperature sensor (not engine temp) was really wrong, it said -16F or something similar. Over the course of a few days it could read -42F or move steadily up to 80 or 100F, when the actual temperature outside was in the 60sF. It was random. It didn't follow any obvious pattern. After a few days of wrong ambient temps, the engine cooling fan came on 24/7, even when I turned the car on first thing in the morning from being stone cold. The dealer replaced the ambient temp sensor in May 2017, but suspected that may not fix it. It just happened again about 2 weeks ago, same series of unfortunate events. The same dealer replaced the ambient temp sensor connector Thursday. We hoped it would do the trick, but it hasn’t. I got in after getting the car detailed a day after the repair and the temp read -16F on a 38F degree day. With it still playing up and sending fault codes, it won't pass emissions, which is coming due next week, and I need this fixed as soon as possible to sell the car in good working order. I don’t want to put more and more money chasing this, and I can’t afford to do that, so I welcome any help and expertise. Thank you!

[Crasher]

Is the outside temperature display still wrong? Has the car ever been involved in a front end crash?

[Kai AndersFinn]

Hi Crasher,

I just took it out to see what was up with it today and the outside temp gauge is close to right, which is what it's been since I've had the car for the last 6 years. It's never been super accurate, but it's behaving normally today. I haven't had any front end crashes, and when I bought it with about 11,000 miles Carfax report showed one rear end fender bender that didn't even cause the air bags to deploy. I did run over a decent sized stick that went under the car that I couldn't avoid a few days before the first time the temp gauge started this last May. I suppose that could've caught on a wire, but I told the mechanics this last May.

[Crasher]

If the reading is approximately correct then it won't be the problem. I had a Golf 5 from a trader the other week that had obviously been in a front end smash and the sensors two wires were twisted together making the outside temp read about 150 and the fans were going ballistic so I twist wired in a 2K resistor which made it read 7 ish and the fans shut up. This was just to prove the point but being a car trader he was happy with the cheap fix as it was-typical!

[Kai AndersFinn]

If the reading is approximately correct then it won't be the problem. I had a Golf 5 from a trader the other week that had obviously been in a front end smash and the sensors two wires were twisted together making the outside temp read about 150 and the fans were going ballistic so I twist wired in a 2K resistor which made it read 7 ish and the fans shut up. This was just to prove the point but being a car trader he was happy with the cheap fix as it was-typical!

It passed emissions yesterday, so by some miracle it didn't send a fault last week when the temps read wonky. It only did it that one day and behaved the rest of the week. Now I'm free to sell it with full disclosure to the new buyer. Who knows, it may never do it again, but the $500 I put into this issue so far is all I have the stomach for. It may be done or it may wait until next April to have it's annual freak out. Thanks, this is a great forum.