Which protocol is used on the vehicle bus?

[green_chicken]

Hi guys,

I have a Fabia III (NJ) and wanted to read the signals which are being send on the vehicle's bus system. Therefore I have to know the protocol of the vehicle.

Did anybody of you successfully listen on the bus of the car to read some values? Is it even possible to read let's say rpm witha proper device which is connected to the OBD-II connector of the car?

 

Best regards

Edited 22 October, 2017 by green_chicken

[roo]

It runs off of a can-bus system, and it is also compatible with the international OBDII specs.  

The most comprehensive for reading values and the like is VCDS from www.ross-tech.com and it runs via a laptop.   Another option is OBDeleven which runs via an app, but apart from a few system changes I am not sure what it does. 

Personally I use VCDS.  The dongle is not cheap, but it's worth it in my eyes, but then again I've had the lead for 12 years and it has paid for itself a few times over after helping people over the years, plus for my own curiosity and use.

Edited 22 October, 2017 by roo

[green_chicken]

OK I guess you mean the "HEX-V2". I'm not quite sure if you understood my question because of you writing "a can-bus system" like some kind of can-bus system.

I'm looking for the actual protocol. If you could have a look at this sheet you see that the different Fabia models use different protocols (= 3rd last column).

https://www.blafusel.de/obd/obd2_scanned.php#1641

I have to know the specific one so I can look for a cheap (and open source) solution.

What I want to archive is something like this: 

 

What you've posted seems like a very commerical solution with fixed functionality? Or is it possible to sniff all the CAN traffic, filter for changing values of specific CAN-IDs and send custom packets on the bus?

 

Edited 22 October, 2017 by green_chicken

[langers2k]

Something like CANable or CANtact should work.

 

Might be worth taking a look at socketcan and find a USB interface that's compatible.

 

edit:

Remembered the name of the interface I have, it's a USBtin. It's just another piece of socketcan compatible hardware

Edited 22 October, 2017 by langers2k

[green_chicken]

So it really uses CAN protocol (= ISO 15765) and not "some kind of CAN protocol"?

The above answer did not make that clear to me sorry.

 

I just ask because no Fabia model in the past used the ISO 15765 according to the datasheet. I also don't know if CANable or CANtact support any other protocol than CAN.

[langers2k]

ISO 15765 isn't listed against any Fabia on the webpage you gave, it's only mentioned once and that's for a Ford Ka.

 

There will be other protocols such as LIN-bus used for slower/less important things (front wiper motor, rain/light sensor).

 

As for CAN-bus, your Fabia probably has more than one CAN-bus network, for instance my '61 plate Octavia at seven I know of:

- Convenience

- Drive chain

- Extended CAN

- Dash panel (instrument cluster)

- Diagnostics

- Infotainment

- AFS (xenon range/cornering/levelling)

 

Each CAN-bus runs at a different speed so make sure you set that correctly when tapping into them.

 

As a starting point, find a wiring diagram for your car so you can find the CAN gateway and understand what is connected to each of it's CAN-bus networks.

 

I have a USBtin and I was able to record CAN packets using socketCAN so I'd be very surprised if USBtin/CANable/CANtact were incompatible with your Fabia. All three should all be able to receive and transmit the raw CAN packets using socketCAN. In the Toyota clip, "candump" and "canbusload" are free but "toyothack" is something the video creator made to parse the data from socketCAN. You'll need to make your own version specific to the messages used by the Fabia.

If you're waiting for someone to tell you exactly what it's using you're probably going to be disappointed as this is far beyond what most forum users understand. It might be work reading some of the VW self study programs (SSP), I think 186, 238, 269 and 517 are all CAN-bus related.

 

Be interested to hear what you're actually trying to do and how you get on though  

[lowedb]

CAN bus is a protocol in itself. There is also a communication protocol that sits on top of it that is manufacturer and even model specific and therefore hard to get information on. You won't find VAG giving that away any time soon, and a very small number of people who understand much about it.

 

I think what you are asking about is the diagnostic communication protocol implemented over the CAN bus. That's also because you are talking specifically about the CAN bus that you can access via the diagnostic plug, and that is diagnostic CAN. You don't get access to all of the data that's on all of the CAN systems through that. As far as I know ISO 15765 is UDS, and that would kind of stack up that Fabia didn't get UDS until the Mk3. Now the point about UDS is its an open protocol so information about it ought to be much easier to come by, though the details of which services are supported are still somewhat vehicle specific.