CAN Bus, are we analyzing the whole signal? The uScope is still more powerful than it seems…

Justin Technical Support Specialist California Posted   Latest   Edited  
Demonstration
AESwave
Education
Network Communications
Can Bus Signal Distortion
Uscope
Network Diagnosis

Awhile back I started writing an article, which follows this short prologue. I have admittedly, been a slacker and did not diligently finish this article. Until now that is. I recently saw a case study that was posted in some of the technician groups we all frequent on Facebook. The case study , produced by Mario Rojas, was the catalyst to finally finishing my first real write up. As an epilogue of this article you will see some of the captures that Mario was faced with, and why I wish I would have finished this article when I first set to writing it. At the end of this article I will , with his permission, use some of his captures as further evidence to support the article from a real world standpoint.

diag​.​net/file/f4ruohgnf…

Here is a screenshot from a recent case study done by Mario Rojas (Super Mario Diagnostics) you can see the effect the electrical system had on the CAN signal measured. Thank you to Mario for allowing me to borrow a part of his case study to push this concept from theory to actual application. diag​.​net/file/f3gff5ilp…

As you can see, without the combined signal math channel, it would be very easy to call the CAN H and CAN L signals as distorted or bad. But as you watch the case study, you will see that would be a bad call. I encourage all reading this article, to watch the entire case study, to see the situation and the outcome. The entire Case study can be viewed at : youtu​.​be/BEiu6JcpSew

Special thanks to Jorge Menchu, Carlos Menchu, and Matt Fanslow for reviewing and editing my horrible grammar and spelling. It's been in progress, just barely less than a year......

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Bill Owner/Technician
Michigan
Bill Default
 

Thank you Justin & Mario for taking the time to highlight this issue and explain it!!

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Justin Technical Support Specialist
California
Justin Default
 

Thanks for the support Bill!

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Dmitriy Analyst
Ontario
Dmitriy Default
 

I am going to be that grumpy voice in the corner muttering: "But what about the common-mode limits?" If the interference gets bad enough, and the signals fall outside certain limits (standard values are -2 to 7V, though many receivers support wider ranges such as +/-12V), the message will not be transmitted correctly even if the difference between CAN High and Low remains valid and nice…

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Dominick Technician
New Jersey
Dominick Default
 

nice, great job

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Thanks
Geoff Diagnostician
Hawaii
Geoff Default
 

Great article. Love Mario!! His videos make auto repair/diag look fun. Then I go back to work and....grrrrr

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Justin Mobile Technician
Utah
Justin Default
 

Looks familiar. Here is my post on Facebook from last May. This mess was caused by a power line near the vehicle I was testing.

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Justin Technical Support Specialist
California
Justin Default
 

Wild, not sure how I missed that case from you. I would love to read the whole thing Justin.

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Justin Mobile Technician
Utah
Justin Default
 

It was just minor blip. No real write up.

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Cody Diagnostician
Arizona
Cody Default
 

Does look familiar, crazy how a power line and a throttle body can resemble in noise

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