Anyone With CAN Bus Sniffing Experience? - Page 2 - Pontiac Solstice Forum
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post #16 of 27 (permalink) Old 02-26-2019, 04:50 AM Thread Starter
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I was half-right about the terminators. One is in the ECM but the other is between the BCM and the DLC.
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post #17 of 27 (permalink) Old 02-26-2019, 06:57 AM
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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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post #18 of 27 (permalink) Old 02-26-2019, 10:02 AM Thread Starter
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Quote:
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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.
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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post #19 of 27 (permalink) Old 02-26-2019, 11:21 AM
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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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post #20 of 27 (permalink) Old 02-26-2019, 11:57 AM
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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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post #21 of 27 (permalink) Old 02-26-2019, 01:17 PM Thread Starter
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I believe that the bus can function without the terminators, but the reflected signals can (and usually do) cause a lot of communication problems.

We probably still have the token-ring wiring in the walls.....

We use Device-Net for some machine control, or we will until we get the rest of it ripped out. It is a CAN Bus that is incorrectly used for field device wiring.
The worst thing when there is damage to the wiring is that everything goes down and there is no way to easily find the problem.

Fortunately for us, the car is a protected environment (until people start modifying things) so network integrity is generally pretty good.
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post #22 of 27 (permalink) Old 02-26-2019, 01:22 PM
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That may depend on the topology. If its a star network, then "termination" really doesn't mean anything. If the devices are in series, then it might be a different story. How are the devices you work with configured (wrt topology)?

That's just my half-assed attempt at armchair circuit analysis; I haven't dealt with the physical layer on CAN.

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post #23 of 27 (permalink) Old 02-26-2019, 02:00 PM Thread Starter
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Device-Net is daisy-chained, just like the high-speed LAN in the car. Star is much easier to troubleshoot. That's one reason the the industrial control world is moving away from it and toward Ethernet/IP
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post #24 of 27 (permalink) Old 02-28-2019, 05:03 PM
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Funny (not!) DeviceNet story. A customer bought an old box making machine. It had to be disassembled into 10 separate control panels, shipped across the country and re-assembled. All of the I/O was DeviceNet - 54 nodes. When reassembled, you could occasionally get all the nodes on-line, but more often, you'd be missing anywhere from three to 25.
Thinking this was a new development (I never saw the machine run), I'm looking at connections, failed devices, just about anything - except the terminations.
After a couple days, I decide to start from scratch. Sure enough, there are five bus terminations. The two at either end of the network (like you'd expect), and three encoders with integral terminators switched 'on'. My guess is, as the encoders failed and were replaced, who ever installed them didn't know any better.
Probably thought they were getting rid of a lemon when they sold it.
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post #25 of 27 (permalink) Old 02-28-2019, 10:41 PM
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Quote:
Originally Posted by JohnWR View Post
Fortunately for us, the car is a protected environment (until people start modifying things)
It just occurred to me that you (and maybe we) are now introducing into the car an entirely new set of failure modes by futzing about with this stuff.

Muahaha.

If you need sniff logs, let me know and I *may* be able to help, time, etc. allowing. Send me a PM or whatever.

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post #26 of 27 (permalink) Old 03-01-2019, 12:01 PM Thread Starter
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I am sincerely hoping (expecting, really) that there will be no new failure modes caused by my futzing.

I am monitoring only, and only on the low-speed bus, so unless I do something really bad there won't be an impact.

My hardware should be here soon and i will start the serious futzing, then we'll see what happens.

Thanks for the offer, I may take you up on it. I will also be posting information about whatever I find.
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post #27 of 27 (permalink) Old 03-01-2019, 01:27 PM
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I am sincerely hoping (expecting, really) that there will be no new failure modes caused by my futzing.

I am monitoring only, and only on the low-speed bus, so unless I do something really bad there won't be an impact.

My hardware should be here soon and i will start the serious futzing, then we'll see what happens.

Thanks for the offer, I may take you up on it. I will also be posting information about whatever I find.
When you start futzing with it, start a new thread with results, etc. I am really interested in getting into CANBUS stuff and the Kappa platform seems like a great way to start. As I understand it, it has a single high speed and low speed bus unlike my CTS-V that has like 4 low speed buses. I have the hardware and would be happy to assist, just so I can learn myself.
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