Audi and Electricals (Kinda Long)

[mkb]

Cody,

Thanks for the input.  When I was fixing the wiring in the shifter, I also 
checked the TCM, and it appeared bone dry.

Based on your suggestion about my flawed logic, I think it's time to either get 
ELSAWin or just buy a copy of the Bentley for the A6.  I've found used versions 
on Amazon for around $60.

Also appreciate the tips on checking  the circuits.

--
mohammed
99 a6 2.8q avant
97 a4 1.8tqa



----- Original Message ----
From: John Cody Forbes <cody at 5000tq.com>
To: mkb <mkb125 at yahoo.com>
Cc: "quattro at audifans.com" <quattro at audifans.com>
Sent: Tue, September 21, 2010 11:21:00 PM
Subject: Re: Audi and Electricals (Kinda Long)

30 is the battery POSITIVE. 31 is ground. 

I think your logic is flawed about the wiring diagrams being the same between an 
A4 and A6. They have different equipment and a different layout. I wouldn't 
expect any ground points nor supplies to be the same. Find yourself a copy of 
ELSAWin which covers these models well and can be had free on the web.

With transmission problems on any modern VAG product one of the first things is 
to get to the trans controller under the passenger seat and check for moisture. 
It is very very common to find the floor wet and the trans ECU fried. Typically 
I remove the control unit and pour out a cup or more of water. On occasion the 
thing comes back to life after being dried, but I'd never bet on it.

In my opinion, after checking for moisture, you need to figure out which pins on 
the trans controller are circuits 15 (switched power), 30, and 31. Then use a 
DMM to check that they are actually what they should be... Within .5v of battery 
voltage at circuit 30, the same only when the key is on at circuit 15, and close 
to 0 ohms from the circuit 31 wire to a known good ground. If these check out 
you could have a bad TCM. If they don't check out THEN it's time to start 
working backwards up the system to find the source of the problem.

-Cody (mobile)

On Sep 21, 2010, at 11:05 PM, mkb <mkb125 at yahoo.com> wrote:

> 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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