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Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » CANbus Frames

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Author Topic: CANbus Frames
Mohy
Member
Posts: 31
Post CANbus Frames
on: March 8, 2022 (GMT)

Hi,

I am trying to decode CANbus frames from my Toyota, This is a sample of what Torquescan explorer of CANBUS communication comes up with:

Line “Frame ID” “Frame Data”
1 002 002000018B
2 003 0030002000002A
3 010 010E
4 019 0190880432B
5 020 0200000FA
6 022 022020101FE0000002C
7 023 0230206020600003A
8 025 0250FF61002787878AC
9 028 0280FEC0004FEB000DD
10 04F 04FEB000DD

I reviewed the ELM327 DS and searched on the forum and cannot find any description to properly understand how to decode the above frames. Any help taking the above as examples would be much appreciated.

Many Thanks

piemmm
Administrator
Posts: 6623
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

Hi!

Canbus frames are mostly manufacturer specific and the plugin can record them so a DBC file can be made or adjusted. You will need to know what each frame id is (without the manufacturers aid, this has to be manually worked out most times)

DBC files for toyotas are on: https://github.com/commaai/opendbc which can then be directly imported into the extrended PID editor (in the settings) – the DBC file itself is text and will give you a good idea what the canbus frames contain

Mohy
Member
Posts: 31
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

Thanks, I realized this. But wanted the rules for dissection of frame (where is the pid and where is the payload), so I can try to figure out which frame provides the gear position.

According to the docs I read the frame starts with a few bytes indicating pid then length of data bytes then a crc.

However, what I see above is inconsistent with this rule.

piemmm
Administrator
Posts: 6623
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

Hi!

These are not MID/PIDs, they are can frames which are broadcast frames at a set rate on the vehicle bus – they bear no relation to mode 21, 22, or 01 PID requests

The can frame starts with the frame id (the first part of the frame) then the payload after that and are usually 8 bytes or shorter in length.

There is no ‘rule’ for it as such as the data is usually crammed into the frame as bits, bytes, etc – this is why DBC files usually work at the bit level

Mohy
Member
Posts: 31
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

HI,

Thanks for this.. So I guess sniffing this is not the right path.

piemmm
Administrator
Posts: 6623
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

Hi!

It’s probably more useful to use the PID scanner part of the plugin and let it trundle through some more 21 and 22 PIDs (then you will have a list, with data which is likely what you want that you can export)

Then it’s a case of either monitoring that PID for changes (open door, close door, look for a change kind of thing) or finding the relevant documentation from the manufacturer (if you have access to that)

Mohy
Member
Posts: 31
Post Re: CANbus Frames
on: March 8, 2022 (GMT)

HI Ian,

Thanks much. I will post my findings (if any) on the forum. Would be nice to have a sticky thread for each brand so we could collectively publish our findings in one place..

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