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Thread: Low Speed GMLAN Interface

  1. #1
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    Low Speed GMLAN Interface

    Ok, I’ve been looking around this board for a while, so now for my first post.

    I am looking for a low cost off-the-shelf Vehicle to USB or RS232 adapter for the Low Speed GMLAN. At this time I do not wish to start from scratch and build my own interface, maybe in the future if my ideas pan out.

    This is not an OBDII device, nor will any of the ELM based devices work.

    Purpose is to explore the bus and operate a few items like the door locks. I have read of someone using only the CANHi side of a Two-Wire CAN to read the bus, but this was not a stable platform and sending commands sounded iffy.

    On my vehicle the ECU, TCU, Brakes and Steering are on the 2-Wire Hi Speed GMLAN or “CAN” operating at 500kps. All other communications within the vehicle are on this Low Speed Single Wire CAN.

    There’s been some recent activity on this forum regarding this SW CAN.

    What I know: well think I know
    GM’s “Low Speed GMLAN” is a Single Wire CAN operating at 33.33kps.
    It conforms to SAE standard J2411 & GM standard GMW3089.
    Its Higher Layer protocol is OSEK.

    To help others wishing to develop a project the following CAN transceiver chips interface with it:
    NXP AU5790 SEE IMPORTANT NOTE IN POST #34
    Infineon TLE6255
    Melexis TH8055 or 8056
    Freescale 33897
    On Semiconductor NCV7356

    Anybody make what I am looking for?

  2. #2
    E85
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    Quote Originally Posted by Hebe View Post
    Ok, I’ve been looking around this board for a while, so now for my first post.

    I am looking for a low cost off-the-shelf Vehicle to USB or RS232 adapter for the Low Speed GMLAN. At this time I do not wish to start from scratch and build my own interface, maybe in the future if my ideas pan out.

    This is not an OBDII device, nor will any of the ELM based devices work.

    Purpose is to explore the bus and operate a few items like the door locks. I have read of someone using only the CANHi side of a Two-Wire CAN to read the bus, but this was not a stable platform and sending commands sounded iffy.

    On my vehicle the ECU, TCU, Brakes and Steering are on the 2-Wire Hi Speed GMLAN or “CAN” operating at 500kps. All other communications within the vehicle are on this Low Speed Single Wire CAN.

    There’s been some recent activity on this forum regarding this SW CAN.

    What I know: well think I know
    GM’s “Low Speed GMLAN” is a Single Wire CAN operating at 33.33kps.
    It conforms to SAE standard J2411 & GM standard W308GM9.
    Its Higher Layer protocol is OSEK.

    To help others wishing to develop a project the following CAN transceiver chips interface with it:
    NXP AU5790
    Infineon TLE6255
    Melexis TH8055 or 8056
    Freescale 33897
    On Semiconductor NCV7356

    Anybody make what I am looking for?
    Coincidental . I am looking for a source of the SW CAN transceiver chips and google came up with this page.

    Is your car a Pontiac G8? They certainly have the the HS CAN/SW CAN split as you describe.

    Thx.

  3. #3
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    My vehicle is a 2009 HHR.

    It is my belief that all GM vehicles since ~2006 have both the Low and High Speed GMLANS, but what do I know.

  4. #4
    E85
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    Quote Originally Posted by Hebe View Post
    My vehicle is a 2009 HHR.

    It is my belief that all GM vehicles since ~2006 have both the Low and High Speed GMLANS, but what do I know.
    Well...you do know what you are talking about as that is pretty well correct from 06 on, some 05 but not much.

    Are you mainly interested in the LS CAN for ICE/entertainment reasons?

  5. #5
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    I don't understand the "ICE" term.

    However, I wish to intercept the door lock and unlock command from the remote receiver and the chime on and off commands.

  6. #6
    E85
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    Quote Originally Posted by Hebe View Post
    I don't understand the "ICE" term.

    However, I wish to intercept the door lock and unlock command from the remote receiver and the chime on and off commands.
    Sorry...TLA: three letter acronym..."In Car Entertainment": ICE.

    Yes that will need the LS CAN.

  7. #7
    VENDOR - ScanTool Vitaliy's Avatar
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    I think that it's possible to use an ElmScan 5, by replacing the CAN transceiver with a SW version, and rewiring the pins to go to pin 1 of the J1962. Then you configure one of the user CAN protocols for 33k, and you should be good to go.
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  8. #8
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    Quote Originally Posted by Vitaliy View Post
    I think that it's possible to use an ElmScan 5, by replacing the CAN transceiver with a SW version, and rewiring the pins to go to pin 1 of the J1962. Then you configure one of the user CAN protocols for 33k, and you should be good to go.
    I had considered doing something like what Vitality suggests and had the following problems with the concept:

    * A review of the ELM product manuals from various manufacturers did not reveal a setting for 33.33K. The settings I found seemed to exclude this speed. Are you definitively saying this speed is available on an ELM product? I had earlier in my quest called ELM and they said it did not support what I was looking at doing. Or perhaps I worded my question to them incorrectly.

    * Since I have been looking into this I have now generated a desire to have a good working unit for general OBDII use after this project and do not want to bugger up a perfectly good unit. I don't know about you, but my soldering skills to repeatedly solder a chip in and then back out seem to destroy pads.

    * I am willing to spend a bit more for both capabilities in one product. So I am still looking around.

    I notice you limited your suggestion to the ElmScan 5 and did not mention your newer product, whose name escapes me. Would it be capable of this as well?

  9. #9
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    ObdPro does a hardware mod that enables you to use the obdpro scantool to talk to the SW CAN. I'm having mine modded as we speak. Seems like there's almost enough demand to enable this by default...
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  10. #10
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    Quote Originally Posted by tripzero View Post
    ObdPro does a hardware mod that enables you to use the obdpro scantool to talk to the SW CAN. I'm having mine modded as we speak. Seems like there's almost enough demand to enable this by default...
    I thought that OBDPRO used the ELM 327 command set. That doesn't offer a way to set the 'high voltage' state (SW CAN has 3 states). You can't get to some functionality without that, so perhaps they added a superset command or something.

    -jjf

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