Temperature gauge fault.

[luig]

I just thought i would pass this on......

I have a 53 plate 1.9tdi Sport, and a couple of years ago the water temp gauge went a bit bonkers, with the needle going up and down from 0 to 130 as i was driving along.
This was fixed at the stealers under warranty, and the temp sender unit was replaced.
It has work fine ever since......

Until a couple of days ago the needle started at 90 from a cold start up and over 130 when warm.

When the ignition was switched off instead of going back to zero it stayed at 90?!?!

I was contemplating a hefty bill when I thought I would have look myself.

I tried disconnecting the battery for a couple of hours to see if that did anything...but it didn't.

So I had a look at the fuses, and as I was pulling a couple of them out and replacing them, I tried fuse number 27, took it out and put it back in. There was a bit of a whirring sound from the dash board and he-presto the temp gauge has now reset, and gone back to working perfectly again!

I wonder how much the stealers would have charged?

 

[beezanick]

I had the same problem with my fuel gauge.

I have an aftermarket warenty with my car so got seat to diagnose the fault so I could get it fixed. They said it was a faulty instrument cluster, and would be £400+ to fix it. I then had the battery off when I was fitting cruise control and when I reconnected it, the gauge was fine! Told seat - and they wouldnt believe me! I explained that it must have an auto calibration, and this had happend when I disconected the battery. Their response was that I didnt know what I was talking about and their technisions knew far more about it electronics than me, that it was imposible for that to have happend, and that the instrument cluster was definatley faulty and would not have just needed a 'reset' and I should listen to them cos they knew what they were doing. I should also get a new cluster fitted by them to solve the problem.



I then explained I am an electronics engineer, and such feats are indeed possible. They were welcome to look if they wished. They soon saw I was correct.

 

[luig]

Just goes to show how much they (stealers) actually know!

I am now thinking that when my gauge went haywire the first time, this fix might have worked?

 

[beezanick]

Quite possibly, I had the battery disconected for about 5 hours, although I would guess it would would work with a shorter period. It is certainly worth a try to see if you could save yourself £400.

 

[RUM4MO]

I had the same problem with my fuel gauge.

I have an aftermarket warenty with my car so got seat to diagnose the fault so I could get it fixed. They said it was a faulty instrument cluster, and would be £400+ to fix it. I then had the battery off when I was fitting cruise control and when I reconnected it, the gauge was fine! Told seat - and they wouldnt believe me! I explained that it must have an auto calibration, and this had happend when I disconected the battery. Their response was that I didnt know what I was talking about and their technisions knew far more about it electronics than me, that it was imposible for that to have happend, and that the instrument cluster was definatley faulty and would not have just needed a 'reset' and I should listen to them cos they knew what they were doing. I should also get a new cluster fitted by them to solve the problem.

I then explained I am an electronics engineer, and such feats are indeed possible. They were welcome to look if they wished. They soon saw I was correct.

I think that there is a calibration procedure for a few function like gauge read-outs in VAG-COM. I once mentioned "VAG-COM" to a VW dealer (not the one I use normally - just in case!) and their service head receptionist gave me a right "going over" as firstly VAG-COM will break the car and secondly, unless you buy the proper VAG-COM costing £4000 then nothing will work - this was backed up with "I've bought the proper one and I know what I'm talking about"! Strange, as this dealer had previously also told me that instrument panels can not be recoded, my car was an import so washer liquid low warning was not enabled - "you need a new instrument panel to sort that one out!". Strange thing was that I enabled that feature and the brake wear feature in a couple of minutes!! Dealers, eh, but sometimes you do need them, my experiences of doing early oil changes first alerted me to some bullsh*t being kept for feeding to customers who think that they know what they are talking about!

 

[RUM4MO]

Quite possibly, I had the battery disconected for about 5 hours, although I would guess it would would work with a shorter period. It is certainly worth a try to see if you could save yourself £400.

This is not the first time that I have seen this topic being discussed - can't remember where or what the root cause of the problem was though in these other cases.

I've always been a bit wary about exactly how this temperature gauge works, I've always considered that while the display is an analogue device, it is not being fed with a continuously varying voltage input signal, more that it is being sent maybe only 5 or 6 voltage levels which relate to the current engine temperature being seen by the ECU. As you say if even one data bit stays set then the reading will start off being incorrect. Not quite like the "old days" when an instrument panel voltage regulator could go faulty and increase the fuel level and drop the engine temperature readings.

 

[beezanick]

I just find it a bit anoying when the dealer - who should know about the cars - tells you a load of lies and then treats you like you know nothing about the subject of cars...

I would guess that the dials will be some kind of stepper motor, and would need to be set to their start positions - hence the calibration. The dealer still insisted it could be the fuel sender, even though the gauge read 1/4 tank when the ignition was off. They wanted £70 + vat to see if it was the cluster or the sender, which I think was a bit much! I sugested I should go elsewhere, and they agreed to do it for free (I had to have it diagnosed by them for my warrenty). How kind.