Audi and Electricals (Kinda Long) C5/A6

[Chris Semple]

30 is battery positive in Bentley speak. One note from the KISS school 
of auto tech, before chasing wiring connections with a meter, pull up 
the RF carpet and have a good look at the TCM(trans computer). That 
series of cars isn't known for electrical troubles, and it does seem 
that your issue is "narrowed" down to the trans circuit. They are 
however, known for flooding out the floorboards which includes the TCM 
on the RF and the CCM(comfort/conv module) on the LF. Audi 
half-engineered the plastic box containers for these ecu's, which means 
that they created a box for these things to live in(good) but didn't 
weatherseal the box or provide drains in the box(bad). So even a 
smallish amount of water getting in there will have a hard time getting 
out. I've used baggies and shrinkwrap as a preventative measure on some 
cars. Inspect the TCM for water damage, including the harness. I've sold 
plenty of TCMs, occasionally with harness pigtails. Even bought cars 
from dealers who were sure they were "junk" :)

-Cheers
-Chris Semple
Concord NH
'84 4000q
    '08 E350 Club
        '04 F350 DRW
> Hi Folks,
>
> So I'm trying to sort out my A6.  Seems to have some electrical issues most of 
> which I think I have sorted out.  I think I've got one major issue to resolve 
> but I'm no electrician and I'm having a tough time trying to understand wiring 
> diagrams but I think I understand a little more than I did a few weeks.
>
> So here's the situation.  My VAG-COM reports the following:
> 00668 - Supply Voltage Terminal 30
> 31-00 - Open or Short to Ground
>
> This is reported by the transmission control module (TCM) on the VAG-COM so I 
> assume that the TCM is not getting enough supply voltage.  Why do I say this?  
> Because the transmission range display on the dash lights up.  I can reset the 
> code and the display shows correctly until I restart the car.  I also know (I 
> think) that Terminal 30 is the negative (right?) post from the battery that 
> supplies the various components with power.  I assume that all the other 
> components are OK because only the TCM is throwing the open or short to ground 
> (right?).
>
> Now, I could clean the battery ground and the ground strap on the starter, but 
> since I only see the TCM throw an error, I assume that the ground connections 
> are good.  So then there must be a wire from the battery that supplies the TCM 
> with voltage and that must have a short somewhere from where it connects from 
> the power source to the target module, the TCM in this case.
>
> Right now, I'm looking at a wiring diagram for a auto tran with tip from my 
> Bentley for an A4 (repair manual page number Y429).  I'm assuming it's going to 
> be pretty much the same if I look under the same engine code and year.  And I 
> see a red wire from terminal 30 go to A40 which is a plus connection in the 
> instrument panel wiring harness which then goes to T15g/11 which is a 15 point 
> brown wire connector station right, A-pillar.
>
> Folks, bear with me.  I've been trying to complete this post for the last two 
> hours referring to the Bentley and trying to understand and write something down 
> without sounding like an idiot.  If you've read this far, I appreciate it.
>
> OK, so after some hours of thought, I think my plan of attack is to go to the 
> right side A-pillar with a MM, locate T15g/11 (15 point brown connector) and 
> check the circuit there since it's probably the easiest to get to.  I don't 
> really know how to do this, but I figure I'll sleep on it and it'll come to me.
>
> Folks again, I apologize for this long, rambling post.  Hopefully, someone will 
> read it and say "No, you're a complete moron, you're totally off track" or, 
> "Yeah, that seems about right" at which point I'll change my strategy or 
> continue on with plan this w/end.
>
> --
> mohammed
> 99 a6 2.8q avant
> 97 1.8tqa
>
>
>       
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>
>   


-- 

-Chris Semple
Force 5 Automotive
223 South Main St
Concord, NH, 03301
603-223-6700
www.force5auto.com