- Jan 29, 2014
- Reaction score
- VCDS Serial number
Some modules will communicate directly, without a gateway in between VCDS and the module, and others won't (or may be somewhat flaky). I do not think the Gateway adds or subtracts stuff from/to the message headers, but it can do stuff like bit-rate shifting (not all the modules and CAN buses in the car use the 500 kbps expected on the diagnostic CAN bus!) and buffering / message timing adjustments. The normal sequence VCDS uses is to ask the gateway to open a channel to a particular module. The Gateway then responds with something to the effect of, "OK, I'll do that for you, and you should use the following timing parameters". If that negotiation with the Gateway fails, VCDS will still try the module directly (necessary due to the very few models such as the B7 A4 that have some modules that only talk via CAN but have no proper gateway), however this approach may result in less than optimal timing being used, and may not work at all if the module is using a bit rate other than 500 kbps.OK - more questions to the knowledgeable folk here to get the BCM on my test-bench to stop lying about the doors being locked (post #130 above);
First question (and it's a particularly fundamental question - the answer to which I hope does not impinge on any VCDS commercial secrets): Other than operating as the "Fat-controller", what other must-have data does the CAN Gateway provide for successful communications with the VCDS cable. More specifically, I'm trying to understand why when I plug-in the CAN high/low lines from the OBD port on my test-bench directly into the CAN pins on any other control module (with volts connected, of course) - I can't get my HEX-NET to talk. I'm thinking that perhaps the Hex19 module adds/subtracts data from the message header on the other modules - but I'm guessing.
Second Question: Assuming that direct CAN (wiring) connection is possible, what software switch settings should I use on VCDS to maximize the chance of success?
As usual, any response is welcomed - and thanks muchly in advance,
There's also an added consideration: Some modules won't power up (come out of sleep mode and accept a diagnostic session) without other modules being present and telling them, "hey, wake up and smell the coffee" first.