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Thread: GM J1850VPW sniffing and sending commands

  1. #1
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    Jun 2022
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    GM J1850VPW sniffing and sending commands

    Hello,

    I am trying to figure out the J1850VPW commands for door lock/unlock and windows roll up for 2006 Chevy Trailblazer. I am planning to make an Arduino-based controller for these functions. Using a Bluetooth OBD adapter and Serial Bluetooth Terminal application for Android phone, I recorded some messages running on Serial class 2 data bus during doors locking/unlocking and window rolling up/down. Here are these commands:
    Doors:
    68 C4 40 11 1F 1F EF
    68 C4 40 11 00 01 93
    68 C4 40 11 00 1F F8

    Windows:
    68 CB A0 09 02 11 00 00 70 41
    68 CB A0 09 08 11 00 00 70 E2
    68 CB A0 09 04 11 00 00 70 20
    68 CB A0 09 01 21 00 00 70 90
    68 CB A0 09 01 41 00 00 70 4E
    68 CB A0 09 01 12 00 00 70 45
    68 CB A0 09 01 14 00 00 70 2C

    The supposed door commands are composed from 7 two-character bytes, while the commands for windows are composed from 10 bytes. I know that the first 3 bytes constitute the "header" of the message, with the first byte representing the priority and the type of the message, while byte 2 and 2 determining the target and the source module, respectively. Thus, byte 1 [68] is the priority and the type of the message, byte 2 [C4] means door locks, byte 3 [40] - BCM, byte 2 [CB] - windows, and byte 3 [A0] - driver module. However, I am not sure about the meaning of the following bytes, and how they are related to the particular door or window. Could somebody help me to figure out this information? Also, should I change anything while sending a command to the car, mimicking the activation of the door locks or windows? For example, should I use byte 2 [F1] (scan tool) instead of [40] or [A0], or anything else?
    Thanks,

    Anton.
    Last edited by santon; 1 Week Ago at 03:12 PM.