CAN signal decoding

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CAN signal decoding

Postby Belet » Mon Sep 14, 2015 9:10 am

Hi, guys
When it comes to diagnostics on CAN bus, how to confirm which unit the fauty waveform is?
We capture the CAN H and CAN L signals and decode them by Pico 6 Auto software, and we get a list of data such as ID,DLC,DATA Bytes,CRC Sequence and so on.
How can we know the message is from ECM or TCM through the sort of data above?
Many Auto Teches asked me lots of similar questions as they had encountered many troubles dealing with the CAN faults.
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Re: CAN signal decoding

Postby PicoPhil » Mon Sep 14, 2015 9:39 am

Good morning
Thank you for the post about CAN bus decoding. This now becomes a interesting subject and most of the data codes you have listed will only be known by the vehicle manufacturers. This is the DNA of the vehicle and all manufacturers will guard this with their life. All we can do is look at the data files and observe.
Thank you for the post.
Philip
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Re: CAN signal decoding

Postby Belet » Mon Sep 14, 2015 9:48 am

picophil wrote:Good morning
Thank you for the post about CAN bus decoding. This now becomes a interesting subject and most of the data codes you have listed will only be known by the vehicle manufacturers. This is the DNA of the vehicle and all manufacturers will guard this with their life. All we can do is look at the data files and observe.
Thank you for the post.
Philip

Hmmm.....You are right, Phil. But can we get better ways to facilitate it ?
It's a rather hard time for many auto teches when facing problems of CAN.
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Re: CAN signal decoding

Postby Fat Freddy » Mon Sep 14, 2015 10:11 am

J1939 is probably one of the easiest to decode with the right tools. Won't ramble on too much about it but there is some interesting info out there, and I'm no expert.

HTH
FF
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Re: CAN signal decoding

Postby PicoPhil » Mon Sep 14, 2015 11:13 am

Hi Fat Freddy
Agree with your comment and there are thing out if you look.
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Re: CAN signal decoding

Postby Belet » Tue Sep 15, 2015 12:57 am

Hi both,
Thank you for the post.
I got it.
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Re: CAN signal decoding

Postby LM358 » Tue Sep 15, 2015 8:17 pm

You can recognize OBD2-frames because their identifiers all begin with 7.
Take a look at the following:

https://en.wikipedia.org/wiki/OBD-II_PIDs

A good way to get started is to connect a universal OBD-scanner to the car and read the "live data" with the tool. At the same time, you decode the CAN-frames with your Pico.
Try to catch some OBD-frames (with 7XX-identifier). You can even understand the data (all the info is in the Wikipedia-document).
There is a lot of traffic on a CAN-bus, so it can be difficult to catch the 7XX-frames among many others.
The best way to solve that problem is to built an acceptance filter using a µC.
If you have assembly-programmer skills, I can help you with some software for PIC18F258. I don't speak C+ nor C#.

Good luck - Eric (Belgium).
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Re: CAN signal decoding

Postby Belet » Wed Sep 16, 2015 6:48 am

LM358 wrote:You can recognize OBD2-frames because their identifiers all begin with 7.
Take a look at the following:

https://en.wikipedia.org/wiki/OBD-II_PIDs

A good way to get started is to connect a universal OBD-scanner to the car and read the "live data" with the tool. At the same time, you decode the CAN-frames with your Pico.
Try to catch some OBD-frames (with 7XX-identifier). You can even understand the data (all the info is in the Wikipedia-document).
There is a lot of traffic on a CAN-bus, so it can be difficult to catch the 7XX-frames among many others.
The best way to solve that problem is to built an acceptance filter using a µC.
If you have assembly-programmer skills, I can help you with some software for PIC18F258. I don't speak C+ nor C#.

Good luck - Eric (Belgium).

Thanks for your post, Eric.
It really helps a lot.
I will take account of it and try it. :D
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Re: CAN signal decoding

Postby Steve Smith » Wed Sep 16, 2015 10:47 am

Many thanks to all for the posts.

This is a topic we must pursue as the value of decoding data frames/packets into meaningful data will bring a new angle to diagnosis.

Just being able to identify the presence of a particular control unit would be beneficial when serial data is inconclusive.

One of the tools we can utilise when searching through decoding table is the "Filter"

Within the decoding table, click on the "Filter" option and type in the ID required to list all fames with the required ID.

In the image below, using the "Filter" option and entering ID 5CO will list all relevant data that will help the search for OBDII identifiers. (This will still remain time consuming but will help)

SERIAL DECODE ID.jpg


Take care.......Steve
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Re: CAN signal decoding

Postby Belet » Thu Sep 17, 2015 9:02 am

Thanks for the post, Steve
Filter is a helpful function though faults on Can-bus are real puzzles to auto teches.

Best regards
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