Scanning Can Bus with ELM327

Wildeman101

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Utah
I am wanting to sniff the can bus information on my truck and have found @TJBaker57's info to be very helpful on the topic and get me started in the right direction. I just can't seem to get a good stream of data and also get a lot of random characters; "^M" in my "monitor all" streams. The time stamps aren't showing up either and the data doesn't show up row by row . Any help with getting my app (Serial Bluetooth Terminal) set up to monitor data correctly would be greatly appreciated. Thanks!
 

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TJBaker57

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First thoughts: likely need to change settings for linefeeds and also between line delay settings in serial bluetooth terminal.

Try this...

Screenshot_20211108-105448_Serial Bluetooth Terminal.jpgScreenshot_20211108-105457_Serial Bluetooth Terminal.jpg

Thats the easy stuff. Now are we sure the truck uses protocol 6?? (ISO 15765-4) If it does then the data stream speed will very likely be too fast and you will get a Buffer Full message quite quickly.
 

TJBaker57

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Having had a look at your capture file it does resemble CANBUS (ISO 15765-4). It's quite a jumble there so difficult to decipher. It will become clear when we get the formatting straightened out. Reminds me of my early days online in like 1990, setting modem serial parameters.

What OBD2 adapter/interface are you using?
 

azswiss

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As an interim method for parsing the data you can import the log file into MS Word and then replace ^M with a new line. Taking the first line from your screenshot above:

Capture1.JPG

You will need to do this in two steps:
1) Convert ^ into another character such as *
2) Convert the sequence *M into a new line by selecting Manual Line Break from the Special drop down menu.

The original text above is then reformatted as follows:
Capture.2JPG.JPG
 

TJBaker57

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This is how your CANBUS data will likely look. Here I am monitoring a subset of the data stream and even then I get the Buffer Full error.



12:44:21.686 atmr01
12:44:21.698 184 00 03 00 00 01 FD
12:44:21.698 1C7 07 02 38 FE 03 FC 3F
12:44:21.712 1E5 5C FF 02 70 07 00 02 10
12:44:21.712 1E9 0F C8 00 0C 0F B7 00 1A
12:44:21.720 189 CF FF 0E 70 31 8D FF
12:44:21.731 197 3F FF 00 14 00 00 00
12:44:21.735 19D C0 00 3F FD 00 13 E7 14
12:44:21.743 1A6 04 06 A0 00
12:44:21.750 1AF 20 00 20 14 30 0A 00 FF
12:44:21.752 1EB 01 69
12:44:21.756 1F5 48 08 00 04 00 00 09
12:44:21.763 BUFFER FULL
 

TJBaker57

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What does the "^M" represent in the original screenshot above?

I am guessing this is the result a selection in the serial terminal app?? There are several options for end of line characters. Reasonably certain it is not something on the vehicle data bus.
 

Wildeman101

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This is how your CANBUS data will likely look. Here I am monitoring a subset of the data stream and even then I get the Buffer Full error.



12:44:21.686 atmr01
12:44:21.698 184 00 03 00 00 01 FD
12:44:21.698 1C7 07 02 38 FE 03 FC 3F
12:44:21.712 1E5 5C FF 02 70 07 00 02 10
12:44:21.712 1E9 0F C8 00 0C 0F B7 00 1A
12:44:21.720 189 CF FF 0E 70 31 8D FF
12:44:21.731 197 3F FF 00 14 00 00 00
12:44:21.735 19D C0 00 3F FD 00 13 E7 14
12:44:21.743 1A6 04 06 A0 00
12:44:21.750 1AF 20 00 20 14 30 0A 00 FF
12:44:21.752 1EB 01 69
12:44:21.756 1F5 48 08 00 04 00 00 09
12:44:21.763 BUFFER FULL
Thanks for this example. I was using a cheap elm327 Bluetooth dongle. I haven't had time to go back to it, but I also have a setup to use an Arduino and a can bus shield so that should allow me to get more data without any buffer full issues.

I don't understand why it doesn't show as much information before getting a buffer full message? I understand that it's a faster bus speed and more data is being transferred, but why doesn't it at least read the same number of bytes as your examples of class 2 serial data before getting the buffer full message?
 

TJBaker57

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I don't understand why it doesn't show as much information before getting a buffer full message?


I wonder if it has something to do with the speed at which the data stream is coming in? In your posted example you used an "atma" command. That leaves the floodgate wide open. I used an "atmr01" command which engages a filter so a good chunk of the data is simply allowed to go by without any processing.
 

MRRSM

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FWIW ...If you decide to bump up to using a visual and graphic representation of captured CANBUS serial data activity, the free software from PICO along with purchasing their least expensive PICO-Scope Model #2204A will allow you the chance to probe Two Channels and actually see the data stream breakdown as "Voltage Over Time" representations on the Laptop Screen:

This link describes this 'On Topic' CANBUS Article and a Software Download Tab is also found here. You do NOT require the PICO Oscilloscope to practice with using the PICO-Scope Software Suite:


Presently, this 2 Channel 1 AWG Unit is available on Amazon for around $150.00... Well worth every Penny for use in any or all Automotive Oscilloscope Diagnostics of Electrical, Electro-Mechanical or Electronic and Network Vehicle Components:

 

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