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I am working on a project that needs information from the low-speed data bus and it will simplify things considerably if someone has experience sniffing it and has isolated some of the signals.

Anyone?
 

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There's quite a bit of info out there already.

I found this one helpful (though incomplete):

https://docs.google.com/spreadsheets/d/1qEwOXSr3bWoc2VUhpuIam236OOZxPc2hxpLUsV0xkn0/edit#gid=1

... but you need to know a bit about the protocol first. What interface are you using? What exactly are you trying to build?

I'm using one of these for track days:

https://www.autosportlabs.com/product/racecapturetrack-mk2/

which supports Lua scripting - it can do things like, say, randomly change your radio volume on a set interval, or clear DTCs every 10 seconds, or maybe even something that's actually useful - that will let you write to the bus if you need to poke things. Also happily does CAN logging. You can get something cheaper, like:

https://www.8devices.com/products/usb2can

which might be a little more reasonable for a side project, but you'd have to make a cable to connect it to the OBD port, or to splice it into the harness. (Or this cable might work.)
 

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Discussion Starter #3
Yes, there is a lot of information out there, and there are a number of interfaces available.

How to do it isn't the problem, decoding the messages is the challenge.

I am replacing the radio and need the messages for various warning sounds, power on/off, and instrument light dimming.
 

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The spreadsheet I referenced has message ids, etc. for most of the audio functions. The rest is protocol.


The other way to do it is hook up a sniffer and start triggering the behavior that you’re trying to replicate. CAN isn’t very complex.

Sent from my iPhone using Tapatalk
 

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The spreadsheet doesn't seem to do anything, and the links I tried couldn't access anything. I'll try it again from a different computer.

Yes, I understand how to do it, but it takes time I don't rally have right now. I was hoping that someone already had, so I wouldn't have to.
 

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Okay, time for a really stupid question...
John, if you are just replacing the radio why not use one of the radio interfaces Crutchfield and others sell for that purpose?
 

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The spreadsheet doesn't seem to do anything, and the links I tried couldn't access anything. I'll try it again from a different computer.

Yes, I understand how to do it, but it takes time I don't rally have right now. I was hoping that someone already had, so I wouldn't have to.
There are different pages (tabs) in the spreadsheet, breaking down messages by category.

For audio, for instance, for the steering wheel controls: (Direct link to tab)



The steering wheel controls (these are from an '08 G8, but should be the same as our cars) have a header of 0x100D0060, followed by our bytes indicating function (which button was pressed) and a count. To increase the volume, you'd send

0x10 0D 00 60 00 00 00 xx

where 'xx' is the number of "volume up" presses that you want to send.

Forgive me if I'm telling you things you already know. The spreadsheet also contains some sniffing logs. In the linked-to tab, the C through P columns contain such a log. Many of the tabs for the various CAN functions have these logs.

I saw another collection of
 

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Discussion Starter #8
While I cannot say that I have done an exhaustive search I have looked at a lot of different adapters, and have read all of the radio replacement threads that I could find here. So far all of the adapters that I have looked at either leave out some function, use an internal speaker (instead of the radio speaker) to reproduce the chimes, or have had problems with installation or operation. For some the descriptions are too vague for me to understand exactly what they do and how, and I don't want to buy one and be disappointed.

Connecting to the bus isn't difficult, and neither is converting the CAN messages to the outputs that the radio needs, so I decided it would ultimately be more satisfying to simply assemble and program my own interface, especially since that would also give me the option to do some customizing of the sounds and functions. If Raygun's spreadsheet can lead me to the proper messages that option gets a lot less time consuming.

I have sent emails to some of the interface manufacturers asking for some additional detail, but haven't gotten any responses yet. Depending on what I get back from them, or anyone here for that matter, I may still go the conventional route.
 

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Discussion Starter #9
There are different pages (tabs) in the spreadsheet, breaking down messages by category........
Thanks.

I'll do some more looking through your information now that I have a working computer again.

One concern is that the messages are sometimes not standard, even when you think they would be. I'll give the listed ones a try to see if they are actually the same.

I do know that our steering wheel controls are analog and not digital, so that is an obvious difference.
 

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@raygun: Thank you again for the data. Now that I can actually open the spreadsheet it does appear to have exactly what i was looking for. Testing should be pretty easy and, assuming that GM actually stayed consistent with themselves, you have saved me a lot of time.
 

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@JohnWR

This might make things a little more economical:

Arduino CAN-BUS Shield

If you have an Arduino lying around, this should make things a little easier. There's also decent support / forum activity for Arduino + CAN out there. You'd still need to buy or build a D-SUB to OBD-2 cable. The one on Amazon I linked to earlier *should* work.
 

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No, they are digital. You press a button using your digit == Digital!


:devil:
That is just ... just .... bad. Funny, though.

@JohnWR

This might make things a little more economical:

Arduino CAN-BUS Shield

If you have an Arduino lying around, this should make things a little easier. There's also decent support / forum activity for Arduino + CAN out there. You'd still need to buy or build a D-SUB to OBD-2 cable. The one on Amazon I linked to earlier *should* work.
I have been looking at two options, although neither has some of the functionality of that one. One is really low cost, the other is a bit more expensive, but more convenient.

https://www.amazon.com/XCSOURCE-Receiver-Controller-Development-TE534/dp/B01IV3ZSKO/ref=pd_lpo_vtph_147_bs_tr_t_1?_encoding=UTF8&psc=1&refRID=2ZRVZ2WV1F3A4JVVSS5M
https://www.sparkfun.com/products/14483

In either case, I will have the low-speed LAN wire (and ground) at the radio connector for a direct connection. For testing I will just rig a connection from the DLC.
 

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@JohnWR Well, for those prices, why not?

My soldering skills aren't as great as they used to be, so if I can find something that snaps together, I'll tend towards paying the extra $30 or whatever.

For my data acquisition widget, I'm considering splicing into the CAN hi/lo wires behind the OBD port - though it'd have to be turned off for any diagnostic tool to connect - or just wiring it up as another node on the network, which is a tiny bit more effort. I haven't looked at the physical bus layout so I'm not sure exactly how that works.

This was helpful:

https://www.instructables.com/id/How-to-Hack-and-Upgrade-Your-Car-Using-CAN-Bus/

Does anyone know where the terminator is on the car?
 

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Discussion Starter #15 (Edited)
There are other components that I will be soldering, so a couple more connections are no thing.

I believe that the terminators are in the ECM and BCM, but will check the manual tonight to confirm or correct, unless someone beats me to it.

There is also a pretty good network diagram in the manual. I will post it tonight also, unless ......
 

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Thanks for the pictures. The first one is actually a pretty clean schematic. I don't see a lot of those in service manuals.

I vaguely remember seeing a little black box about the size of a flash drive plugged into the harness over by the DLC, and someone saying that was a bus terminator. But, that was a few years ago when I was swapping the dash on the '06. It could just been that last remaining FBI tracking device that I never located.

Fun (but silly) kill switch idea: add a switch under the dash or wherever that breaks one of the CAN lines. I bet the car would never start if there was a break in the bus. I'll leave it as an exercise for the reader to verify that. :)
 

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Discussion Starter #18
Thanks for the pictures. The first one is actually a pretty clean schematic. I don't see a lot of those in service manuals.

I vaguely remember seeing a little black box about the size of a flash drive plugged into the harness over by the DLC, and someone saying that was a bus terminator. But, that was a few years ago when I was swapping the dash on the '06. It could just been that last remaining FBI tracking device that I never located.

Fun (but silly) kill switch idea: add a switch under the dash or wherever that breaks one of the CAN lines. I bet the car would never start if there was a break in the bus. I'll leave it as an exercise for the reader to verify that. :)
You're welcome.

I think you are correct about the car not starting, as long as the break is between the BCM and ECM. Someone posted with problems starting their car after removing the VCIM, and had to jumper the LAN wires to get it to run.
 

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You're welcome.

I think you are correct about the car not starting, as long as the break is between the BCM and ECM. Someone posted with problems starting their car after removing the VCIM, and had to jumper the LAN wires to get it to run.
I can verify that you need to jumper the wires if you remove the VCIM or the car won't start.
 

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I know the bus has to be terminated in order for it to function, so that's not super-surprising. If the devices on the bus are daisy chained, and you remove one, you get an open circuit.

Anyone remember Token Ring? ("Why is the network down?" "Oh, Bob is rearranging his office and had to move his PC.")
 
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