Direct CAN connection to any module - testing on table

[MartinsX]

Could VCDS interface be used for "testing on table" of modules normally placed behind CAN gateway? And network of modules behind CAN Gateway?
According post #13 here: http://forums.ross-tech.com/showthread.php?7490-Vcds-fault/page2 , its not safe for VCDS interface itself... Are there some CAN filters or line protection devices available?
I'm still fighting this Touareg: http://forums.ross-tech.com/showthread.php?7673-03-Touareg-comm-issue
Tonight I found that 17 and 19 (instruments and gateway) time by time looses comms with diagnostic equipment even with all CAN's disconnected. After disconnecting and reconnecting power, it appears back for some time. Not sure it's cluster itself or something else on K-line, blocking comms to cluster/gateway. Replacement cluster for V10 Touareg is "hard to find" and expensive part here and I have to test everything before looking for replacement one.

 

[Uwe]

Yes, it's generally possible for modules that run CAN at 500 kbps (so for example, modules that are on the powertrain bus). For lower speeds CAN buses, it's not possible because VCDS doesn't waste time trying any lower speeds. The catch of course is that some modules use a virtual terminal 15, where a CAN message from some other module determines whether they are powered up and will talk.

I think you're misinterpreting what I wrote in this post. As long as your test setup doesn't have any really dumb wiring mistakes (such as putting 12V directly on one of the CAN lines), I don't see how it can endanger your VCDS interface.

-Uwe-

 

[MartinsX]

OK, Thanks, Uwe!
So next questions:
- What speed is used on Comfort CAN in 03' Touareg?
- Unfortunately I have 11,5V on CAN-Low wire in this car. Can't find where it comes from, yet.
- Can a separate GW module from another VAG car (some Golfs and Skodas have separate GW) be used for "testing on table" modules with low CAN speeds?

 

[Uwe]

I don't remember the exact speed of Comfort CAN in there, but I think it's quite a bit less than 500 kbps.

I don't know if a separate GW will do. GW in that T'reg is part of the instrument cluster, and an 03 T'reg is mostly TP1.6, while more modern cars with separate GWs tend to be all TP2.0.

I'm not sure what to tell you about the 11.5V on one of the CAN wires. Short it to ground and see where the smoke comes from?

-Uwe-

 

[MartinsX]

There is almost no current on this wire. (No way to get smoke out ) A small test lamp (probably 0,25W or less) didn't lit up, voltage drops to 0 with test lamp connected. I guess it is some oxidation product ("green powder") somewhere inside some module or at some connection point or whatever place where opened contacts or wires with damaged insulation came in contact with moisture and dirt. Main question is WHERE?

Next question: is there some information available what CAN speeds and protocols are used on different VAG cars?

 

[Uwe]

Next question: is there some information available what CAN speeds and protocols are used on different VAG cars?

Speeds of the various CAN buses are usually described in the SSP for a specific model. However, I don't recall seeing much about the protocols in there.

-Uwe-

 

[Zenerdiode]

Main question is WHERE?

Have you tried the basic faulting techniques of disconnecting each control module in turn; noting when the offset voltage disappears?