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D2 - Transmission Gearboxes, diffs, drive shafts.

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  #11  
Old 1st August 2021, 04:07 PM
Simon Wallwork Simon Wallwork is offline
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Oh dear.

Scooshed some WD-40 in there, and refixed the cover- seeing as the fault had gone away.

Took it out on the road and not only is the fault back, but it also does it in tiptronic now too!

I guess next step is remove the TCU and clean its insides?
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  #12  
Old 1st August 2021, 04:23 PM
Simon Wallwork Simon Wallwork is offline
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How the heck do u remove the TCU wiring connector???
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  #13  
Old 1st August 2021, 05:59 PM
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The_Laird The_Laird is offline
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Just picked up on this thread - 37 degrees in Langbank - really?
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  #14  
Old 1st August 2021, 07:50 PM
Simon Wallwork Simon Wallwork is offline
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We moved!
In Bulgaria these days after the job in Kazakhstan ended. My S8 is here now, Tiger will be here (hopefully) in a week.
Actually, I think the heat might be a factor here. Certtainly the ESP/ ABS goes on the blink when it's too hot, but behaves in cooler weather.
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  #15  
Old 1st August 2021, 08:52 PM
MikkiJayne MikkiJayne is offline
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Quote:
Originally Posted by Simon Wallwork View Post
How the heck do u remove the TCU wiring connector???
Unscrew the TCU bracket (two screws at the front) so that it can be lifted towards the front of the car, then unbolt the TCU from its bracket (4x M6 nuts). You may need to lift the ECU out to get the TCU wiring free.
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  #16  
Old 1st August 2021, 11:15 PM
Simon Wallwork Simon Wallwork is offline
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Thanks Mikki.
I shall report back.
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  #17  
Old 2nd August 2021, 09:09 AM
Simon Wallwork Simon Wallwork is offline
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Well, I re-racked the TCU. no difference.

Now took the top off it, looks great inside...

tried the toothbrush and rubbing alcohol on the side you can see, and tipped some down the inside too...

Next, I'll drink the rubbing alcohol if it doesn't work...

hmmm. Board looks Ok at a glance, but looking through a triplex loupe, there's clearly corrosion and deposits all over the place.

I'll let it dry and then put it together, but I think it's likely 'Donald Duck'd' A8 parts don't have a replacement.

Part number is 4D0 927 156 BN

OK put it back in, no joy. Now what do I do!?

Last edited by Simon Wallwork; 2nd August 2021 at 10:44 AM.
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  #18  
Old 2nd August 2021, 01:12 PM
Simon Wallwork Simon Wallwork is offline
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Update.
Cleaned the TCU more and more. Went at it with isopropyl alcohol, toothbrush, cotton buds and scraped between tracks where it looked like it might be corroded.
Fitted it two or three times- each time 100% faulty in tip and auto.

Got bored and decided to fix the two damaged brass ferrules on the box that contains the TCU/ ECU and ABS, so at least once repaired, new TCU might stay dry. I cut a slot to screw them in and bedded them with Superglue.
Decided to build it back up properly and just use it in limp mode while trying to find a new TCU. Flooded the TCU with WD-40 and dusted the terminals with a diamond file.
Built it back up.

Decided to enlist some proper help and said a prayer to God that somehow it would work!

Tried it in tiptronic- still knackered.
Restarted and set off in 4th. Went OK! Drove it in tip and in Auto.
All OK! :-)

Don't know if it'll stay fixed, but all OK for now.
Maybe it just wanted attention??

Gave thanks to God! ('Cos I don't think it was me....).

Last edited by Simon Wallwork; 2nd August 2021 at 02:00 PM.
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  #19  
Old 4th August 2021, 09:52 AM
Simon Wallwork Simon Wallwork is offline
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Well, it didn't stay fixed......;-(

Seems it's some sort of 'startup' fault.

The red lights/ limp mode thing either happens at the first gear change as you move off after starting the engine.

Or else the trip is completely normal.

If the fault is absent, you can drive for hours normally, but the next startup might bring the lights on, with a thump followed by limp mode.

If you start and leave it in tip- first gear- it never comes.
Also, I can start and reverse for as long as I like.

Baffled.

The fault is clearly associated with that first change up- but not all the time.
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  #20  
Old 4th August 2021, 05:47 PM
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johnny_quattro johnny_quattro is offline
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I had my gearbox rebuilt in 2014.

Some time later it started lighting everything on the dash and went into limp-home mode. Called the gearbox specialist and they said it was definitely an electronics issue. Waited a few months and obtained the replacement TCU (thanks Prestige) and it fixed my problem instantly. My original TCU was immaculate; the replacement was not quite as clean and tidy but it certainly did the job. Still working fine 6 years later.

John G
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