RE: VAG scan tool & codes for V8

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> Does anybody out there in Audi land know how the VAG 1551 scan tool
> works?
> I mean specifically what is the communication protocall 
> between the VAG
> and the ECU?
> If I can find this info, I am considering building my own tool. I
> suspect that it is just a faster version of the blink output but have
> not yet put a scope on it to find out.
> As far as scan tools go, are there any good ones available for
> occasional users like me? (meaning cheap)

... well, it must be possible to decypher the coding scheme because there is
already a product available (CarComp/Baum) which could read codes from the
ECU on a PC.  I've noticed in the V8Q service manual that there does seem to
be a fairly involved section on the fast transfer mode, but I've never taken
time to read it carefully.  There may be some clues to get you started in
figuring them out in there.  

Personally, since I can read out the codes with a jumper wire and a light
bulb, and since the V8's ECU doesn't have the logging capability of the
newer cars I've never felt that there would be that much added value for a
VAG1551/1552 tool.  

> And finally, does anybody have a list of fault codes for a 1991 V8Q? I
> am getting codes 3433, 3434, 3443, 3444 and can not find them listed
> anywhere.

I don't have my book here with me, but I'm wondering if perhaps you aren't
seeing codes from the automatic transmission.  There are separate pins that
you short to read engine, transmission and instrument cluster codes.  I
understand that some cars can even read trouble codes from the radio!

HTH!
Steve Buchholz
San Jose, CA (USA)