TDI90 erratic electrics - now Fixed!

Kennedy

A2OC Donor
Hi all, Long post alert!

...my medium mileage TDI90 has had a few electrical gremlins since last year and the symptoms have got much worse this year - now everything is particularly erratic on startup and this is causing multiple systems to error and complete loss of battery power to the dash at times.

In the most brief way I can I'll detail symptoms from last year/earlier this year, and then I'll bullet point the latest list of issues with the electrics that are disabling the car completely, in the hope that it sounds familiar to someone and I can start to trace the possible cause/s.

The car: 2004 TDI90 / 161K miles / general condition 8/10 / No real mechanical issues and drives beautifully...

ELECTRICAL PROBLEM 2019 into 2020 summary:

  • On half turn of key the usual illuminated dash icons you would see would steadily flicker rather than appear 'constant' - I learned the car would never start when in this state, the starter motor would be turning strongly but nothing
  • Turning key back and trying several more times would eventually make dash illuminate with bright constant ABS, battery, glow plug etc lights - the car would then always start
  • When dash lights flickered there was an audible electrical sound possibly from a struggling or faulty relay but appeared to be from the passenger side glove box area
  • Other notable warning from around this time was occasional Oil Level sensor being triggered
  • I realised that the reverse lights or selector switch could have something to do with it, when dash lights in flickering state (car not yet running), selecting reverse would cut all power
  • Then there was an issue that on selecting reverse to park after I had been journeying around in it for a while, the car would completely cut out with all power to dash again cut. Try to start again, flickering dash lights yadda yadda - then would be fine and 2 or 3 more attempts reverse would be fine again.
So, reverse light switch on the selector at fault? - I disconnected this and protected connector and have left it disconnected - now the car never cuts out when selecting reverse but obviously my reverse lights are disabled. Was hoping this may have been the culprit and I could replace switch, but no cigar this time.

ELECTRICAL PROBLEM 2020 current picture:

  • On half turn of key dash is now very erratic, flickering, fuel gauge needle bouncing back and forward like a windscreen wiper, sensors triggering problems with everything from ABS, Oil level, Air Bag etc and even audible warning bongs I've never heard in an A2 before!
  • Way more difficult to try and get the dash to light in a more stable way like in the previous phase, taking up to 10 minutes of trying to hit that sweet spot for everything to work
  • Problem seems much worse on cold damp mornings which I think may suggest some kind of more exposed electrical circuit, wiring or sender shorting repeatedly
  • Audible electrical grumblings still coming thick and fast from the glove box area of the car
  • If I can manage to start the car the power steering is regularly not kicking in and the Air Bag light temporarily displays
  • If I can get the car to start, normally on drier days, it is running and behaving perfectly apart from complete loss of power just once I think (shortly after startup whilst still cold)

The cold damp weather we are now having might well have contributed to things getting worse, the car is permanently plagued by these issues and I can't use it.



Think that's it...Sorry but that's as brief as I can make it to give an accurate picture of all the symptoms!

Does any of this sound in anyway familiar to any owners? Are any of you more Techy members able to offer any thoughts on what I could try to trace the issue...

Help get me back on the road!

Thanks, Kennedy
 
Get the battery tested, are you a member of the AA or such, Park it up at a mac dees and ring them, tell them it won't start and they will check the battery and run a diagnostic, I've done it twice now bef I got VCDS.
 

Think this video might give a better idea of the crazy behaviour if it works...

Cheers for comments already, yes a scan would be useful. Only thing I would say is that the error log will show every sensor on the car is at fault I would think because of constant interruption to the power... but I don’t really understand VCDS at all so will definitely think about getting it connected up.
 
I’ll be checking battery connectors first thing in the morning, I replaced battery with Varta F19 couple years ago so should be decent in itself... but I’ll definitely give that another look.
 
When you check both the battery terminals open up the little black box to the left of the positive terminal and make sure all the connections in the block are tight and the block tight on the battery terminal clamp.
good advice above, in that black box are big flat fuses
, are they tight, any cracks? You mention alot of noises near glovebox, have you had the panel under the carpet in passenger footwell off and looked for anything loose in there too.

I've had the whole dash light up before a bit like yours, that was when my alternator failed and the battery ran flat whilst driving it....
 
So thanks for suggestions so far, had another look this morning.

Battery connections are clean and tight, fuses and connections in fuse box on the positive terminal all good - all contacts had a light clean up anyway just to be sure.

Had a good dig around in passenger footwell and while battery disconnected pulled that apart and removed Comfort unit, ECU and some relays... everything appears to be connected correctly, no signs of shorting or damage.

The main audible noises when the electrics are going crazy are from the ECU, not sure if that means the ECU is at fault.

Only other noises I can detect seem to be behind climate unit but I haven’t had chance to pull that yet...

So yeah still a bit stuck, and going nowhere.

Kennedy.
 
How about the ignition switch, could this have an intermittent connection?

Maybe, seems to reliably engage and switch stuff on but then there’s all the interruptions in power.

As I mentioned before, one alert now displaying is Oil Sensor but I’m not sure if that is simply triggering because of the interruptions in battery power on start up... but, would something like the oil sensor or wiring be a likely point of shorting or failure to cause the above?

Earths have been mentioned, has anyone experienced something like the starter motor earth causing this kind of craziness? - or is it more likely to simply get a click and no turnover? Starter motor is always working on turn of the key by the way.

K
 
...I’ve removed the climate unit, doesn’t actually seem to be much making a noise behind it, stereo and Parrot connections all seem okay.
 
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