Electrical Gremlins - Coolant Temperature Sensor Issue?

[Doobies]

Morning all. First post here, have had the GTI for 3 weeks now and has been awesome up until last night.

Pulled into the drive last night and the temperature gauge jumped to max, and the fans kicked in to high. No other warnings appeared. Shut it down and restarted it and the gauge went back to normal.

Today going to the shops it did the same thing. Restarted it, all good,

Returning home, gauge went to max, then got an auto stop error, lost all throttle response and a message about maximum rpm. Restarted the car and it was back to normal.

Now If I start the car and let it idle, after about 5 minutes the temperature just jumps to maximum and the auto stop fault pops up.


Any ideas? Dealerships aren't open until Tuesday. It is the original battery, the indicator says ok, only drops to 11.2v on cranking and charges at 14v and doesn't appear to be a drop in voltage when the fault occurs.

Dec 2013 GTI 7 with 28,000km


Thanks

[DV52]

Morning all. First post here, have had the GTI for 3 weeks now and has been awesome up until last night.

Pulled into the drive last night and the temperature gauge jumped to max, and the fans kicked in to high. No other warnings appeared. Shut it down and restarted it and the gauge went back to normal.

Today going to the shops it did the same thing. Restarted it, all good,

Returning home, gauge went to max, then got an auto stop error, lost all throttle response and a message about maximum rpm. Restarted the car and it was back to normal.

Now If I start the car and let it idle, after about 5 minutes the temperature just jumps to maximum and the auto stop fault pops up.


Any ideas? Dealerships aren't open until Tuesday. It is the original battery, the indicator says ok, only drops to 11.2v on cranking and charges at 14v and doesn't appear to be a drop in voltage when the fault occurs.

Dec 2013 GTI 7 with 28,000km


Thanks

Doobies: Hi and sorry to hear about your problems. It is of course difficult to be definitive with distance based diagnosis, but it sounds like there is a problem with one of the senders (i.e. either the coolant temperature sender -G62, or the radiator outlet temp sender -G83, or even the air mass flow meter -G70) that are used by the Engine Control Unit (ECU) to decide when to turn-on the fans. All the sensors mentioned are fairly rudimentary devices (simple thermistors), so not much to go wrong really, but as the saying goes - Sh#t happens.

More likely it's probably one of the connectors that connects the sender wires from the ECU to the physical device that has come loose on the engine block somewhere (just guessing). If I had a diagram of your engine, I would post a pic showing where these senders are located -but alas I don't have diagram. Perhaps someone else here can help

Interesting aspect of the temperature senders is that (I believe) VW uses thermistors with a Negative Temperature Coefficient (NTC) meaning that the higher the temperature, the lower the resistance. You would think that if a connector/wire came loose, the resistance would rise to infinity and the engine would think "very low temperature". But as I understand there are smarts in the ECU that ensure that the radiator fan turns-on if the connection fails (and also of course, if the sender develops a short-circuit).

Anyhow, have a general look around the engine bay - you are looking for loose connectors. Pay particular attention to those connectors that have two wires and that appear to be connected directly to a component that is imbedded into the engine block. Sorry that I can't be more precise

Cheers
Don
PS: Another way of getting additional information about your problem might be the start-stop error message that you mentioned. If you press the part of the screen that has this error message, it should take you to a another screen with more detail about why start-stop failed to engage. If you can find this second screen, it might be prudent to take a picture for use when you visit the dealer and for posting here if you want further help.

[AdamD]

If you're in a hurry, search this thread for someone in your area who has VCDS, and PM them to see if they can scan the car for you at short notice. It sounds like there's a good chance this erratic behaviour will have logged one or more fault codes, which should indicate the cause of the issue.

[Doobies]

Well, it's been towed this morning to Osborne Park vw. Its been sitting there 2.5 hrs and no one has looked at it yet. Vw assist organised the tow, would have hoped a tow in warranty job would have been looked at as a priority, seeing I've been without a car for 4 days over Christmas.

Given there is 2 temp sensors that makes sense, I plugged an old generic obd2 scanner in and that showed coolant temp as 93 degrees, while the gauge was in the red.

Will wait and see. If they don't look at it today I won't be happy.

[Doobies]

Well update time. Dealer thinks it's the waterpump. 2 weeks as it's coming from Singapore. Car will successfully be in the dealer longer than in my driveway.

Emailed vw telling them what I think of their repair times and that they should comp the 2 year service which is due next week as good will.

Excited owner of his first vw...

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