CAN BUS Analysis

Caleb Technician Mishawaka, Indiana Posted   Latest   Edited  
Question
Pico Technology
Trained By Techs
Network Communications
2016 Chevrolet Equinox LT 3.6L (3 LFX Flex) 6-spd (6T70)
Many History Powertrain U Codes

Hey guys I have a 2016 Equinox that has acted up 1 time for the customer. She was driving and the guages went to 0, all warning lights an service messages illuminated in the DIC and hard shift and no throttle response. Typical High Speed CAN bus failure symptoms. I know its splitting hairs. However Im not looking for help diagnosing the vehicle as much as wanting to further my knowledge on CAN related issues. Because I live 45 minutes from work I drive intermittents home often so we can catch them in the act or deem no issue at this time. We have had very good success doing this . I hooked my PICO to pins 6 and 14. The vehicle runs fine and there are no codes or symptoms. However I noticed this repeatable pattern as I was driving. 

diag​.​net/file/f7bj4z4tt…

diag​.​net/file/fip5rotw9…

I have also attached the Pico file at bottom with 2 saved screens for you to look at. Anyway there is this nasty glitch and I dont really know what to call it. It is very repeatable. Is this a module putting out bad data in a packet in the second screenshot? In the first screenshot is this singular ( ringing pulse for lack of better term) some sort of diagnostics the bus is doing for itself? I never lose the 2.5 volt bias. It doesnt set any codes, I have not duplicated the concern. Im curious if I pulled fuses to various modules if I could get this to disappear. I have scoped many CAN bus and never seen anything like this on a good network. Anyway I would like some input and discussion. In my personal opinion this is not a terminal tension issue. I have scoped many intermittent terminal tension issues and they never look like this. They always lasted longer and created a much more obscure glitch. When I use the serial decoder it cannot interpret the nasty looking packet. Wether or not that means a module on the car can I have no idea. Thanks guys. 

diag​.​net/file/f2m7nsibq…

diag​.​net/file/f4ro5gn89…

+3
Nick Diagnostician
Affton, Missouri
Nick
 

I've had luck sometimes when I cant see a failure on the network start looking for voltage drops on main grounds and power feeds. I had a Cadillac with the same symptoms but too a step back and found a intermittent 2v drop at the negative battery terminal. Cut off the factory terminal and soldered on a new lug and all was good.

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Randy Diagnostician
Glendora, California
Randy
 

I have one with exact same wave form on a audi . No reason ass why yet

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Joseph Technician
Lexington, South Carolina
Joseph
   

Caleb, I know you said there was no drivability issues but the pattern right when the bus voltage jumps high and those oscillations look suspicious like an ignition firing event. With the design of those coils I would find it hard to imagine one is backfeeding (without a drivability issue) but maybe there is some Can wires near them that aren't shielded and you are getting some EMI. just some…

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Steve Instructor
Irvine, California
Steve
 

What modules set codes and what is the topology of the vehicle. One of the modules is keeping the BUS stuck at its recessive voltage. The ringing appears to an attempt to communicate on the bus. You should have bus off and time out error codes.

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Dmitriy Analyst
Toronto, Ontario
Dmitriy
   

Caleb, from the second graph, is your Can-H bias 2.5V, but Can-L has 2.4V? [EDIT: Oops, this was just an optical illusion from viewing on a tablet. I checked the Pico file and both bias voltages are the same.]

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Christopher Technician
Saskatoon, Saskatchewan
Christopher
 

I don't have a lot of experience a light duty automotive CAN networks but I have done a fair bit on 240k baud and 500k baud used on over the road Volvo trucks which I believe operates on all the same principles. I did have something very similiar on a unit where a non terminated module had a very intermittent voltage drop concern on a hard wired ground eyelet which was loose. Only way to I found…

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Caleb Technician
Mishawaka, Indiana
Caleb
 

Hey guy's! Thanks for all the responses. I was able to get the vehicle to act up an record the data on the way in this morning along with the codes. I have a couple more tests to do along with identifying for sure the module that is causing the glitch. I will try to post everything to tonight. Stay tuned!

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Anything yet? Most cars I see here are still pre-CAN. Hoping someone will put out the "Big Book of CAN Bus Fault Examples" by the time I need to start looking at them.

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Caleb Technician
Mishawaka, Indiana
Caleb
   

Alright guys so I have finally gotten the time to sit down and end this. Like I said I drove the vehicle home the night I posted this 40 miles with no issues. The next morning halfway to work on a smooth flat road at 65 mph it acted up for about 3 seconds. Enough time for me to hit pause on the Pico and get a nice recording of the failure. The symptoms were many service lights and messages on…

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Dmitriy Analyst
Toronto, Ontario
Dmitriy
 

Wow, that was a tough one! Is it possible some equipment in your workshop emits radio interference and adds that funny looking wiggle to CAN bus lines? I have not seen such wiggles from... pretty much anyone else!

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Caleb Technician
Mishawaka, Indiana
Caleb
 

Hey Dmitriy, it's possible. However I also have a mobile diag business and so not all my scoping is done at the shop. I could be 30 miles away.

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