OBD response prefix

OBD response prefix check is not applied to the CAN ID part of the response.

I have found two sensors in GR Yaris that share the same PID but have different OBD Headers (CAN IDs):

Steering Angle
Header: 7B3
PID: 221004

Brake Master Cylinder Pressure
Header: 7B0
PID: 221004

Here are the CAN messages that are generated with such OBD configuration for brake master cylinder sensor:
Request: 0x7B0 03 22 10 04
Response: 0x7B8 04 62 10 04 0A

However responses to the Steering Angle requests also have the same response prefix (04 62 10 04), because both sensors have the same PIDs.

RaceChrono should automatically match responses by response CAN ID, which is request CAN ID + 8. Or full response message with CAN ID should be matched against the response prefix if set in the configuration.

Currently, when I have both of such PIDs configured in RaceChrono, responses are shared across both channels.


  • aolaol
    edited May 21
    OK, so I think what's happening is that RC "combines" the two requests, even when they have different header. It shouldn't of course. I will investigate. RaceChrono does not see or send the full header (to save bandwidth), but I don't think it's needed as it knows which one it should be getting back.
  • aolaol
    edited May 21
    @dvim Can you send your Vehicle profile to tracks(at)racechrono.com, please? I will make sure the exact configuration will be fixed
  • Just sent it. Thanks for looking into this!
  • Thank you, I will let you know once I've investigated it.
  • aolaol
    edited May 30
    @dvim my first assumption was wrong, so there's more going on with it.

    Please follow these instructions to generate debug data. Make sure both "offending" channels are enabled.

    1) Please turn on "RaceChrono > Settings > Expert settings > Save device output".

    2) Then record a session while connected to your OBD-II reader. It is connected if the "Connecting to..." goes away and does not appear again. Short session with GPS lock, and the OBD-II reader connected is ok. No need to be at a race track, just a casual drive around is fine.

    3) Please share that session with me (using the share button, that generates a .rcz file). Please email to tracks(at)racechrono.com
  • I have just tried to record a session with device output, and noticed that the data logged in the session actually looks alright.

    I may have sent you down the wrong path. Initially I noticed the problem in the channel configuration page where live data can be used to see values of all of the configured channels. On that page values are jumping for channels that share the same PIDs. I've sent you a recording of that screen to the email you mentioned.

  • @dvim Thank you for the clarification, it may be indeed a problem only in the test mode. It works a bit differently so it's certainly possible.
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