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Thread: Low Speed GMLAN Interface

  1. #51
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    Quote Originally Posted by regulatre View Post
    Speculation: The AE may be an added byte that tells certain CAN tools which network to transmit to, or other attributes about the transmission... In this case, we would be left with Header="10 02 02 00" Data="00 00", which looks nice, because most commands I've seen are 2-bytes.
    Disagree.
    What you see there is a CAN frame with headers stripped off. That is a request to $AE service, used in diagnostic modes to test actuators, devices etc

    Im curious... what car is it? Whats the ARB ID of this BCM?

  2. #52
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    Interesting how all the experts come out of the woodwork when a challenge is posed

  3. #53
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    It seems this thread just died.... Time to resurrect

    Is there a document which defines the communication protocol used to issue the commands. For example, J1979 is used for OBDII, what is the equivalent for SW CAN?

    Are there any DIY pages for SW CAN?

  4. #54
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    Split - what's your project? What do you want to know?

  5. #55
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    Quote Originally Posted by regulatre View Post
    Split - what's your project? What do you want to know?
    If there is a controlling document that defines the message format and which messages that are available

  6. #56
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    I have a project I will be working on here shortly where I will be doing some stuff with this so I would also appreciate any knowledge that can be shared.

    I have an '03 Chevy Avalanche and plan to start "hacking" the LAN bus in this truck. Eventually I want to talk to the BCM to be able to do things such as turn on lights, adjust the seats etc... I want to replace the OEM stereo with a carpc so I want to learn how to communicate with the devices hooked to the radio. Such as the steering wheel controls, rear entertainment center, XM radio etc... Once I can mimic my Stereo I will pull the stereo and use fully with my PC. I will move onto things such as the HVAC controls and whatever else can be controlled so I can either replace the standard interface with a PC or access them in parallel.

    Information I have gathered so far is that is appears all of the buses in the truck talk with the same ODBII style communications. Have not yet tried to do it though. I will be installing a pc into my truck in the next week or so and will have a scantools unit to start playing with it.

    Rodney

  7. #57
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    so back on mp3 car after a number of years of inactivity. Instead of posting a new topic or messaging a bunch of people with the same question seems logical to post here.
    i too need some help with both the high speed gmlan and the gm class 2 serial data. I am after a device that will allow me to read code or get packets whatever it is that is broadcast over the class 2 serial data line when the tow/haul mode switch is enabled and disabled. Long story short putting an allison transmission from a chevy duramax truck behind a cummins. for the tow haul feature to work for the transmission the connect to ground signal from the tow haul button is sent to the body control module, the body control module sends over the class 2 serial data line a signal or code, or packet to enable tow haul mode that is recieved by the transmission computer wich enables tow haul mode.

    sure i could wire in the body control module wich i have and would work fine, but rather not have to wire in 11 wires (various power, grounds, 2 data wires, and tow/haul input wire) just for one feature to work. that and its a slightly larger box that i would rather not have to run. I would rather have an arduino or other simpler/smaller microcontroller replicate the signal that the body control module is outputing when the tow/haul button is depressed.

    hope someone can help, and hope there is an existing scan tool type device that can help receive the information I am looking for. Seems most are after hacking gmlan or class 2 serial dat for entertainment purposes where i am after a transmission related feature. and eventually ill be interested in the gm high speed lan for engine and transmission related projects.

  8. #58
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    What year vehicle are you working with? I have a 2003 Avalanche 1500 that I am dealing with. I am still finalizing my PC installation after which I will be playing with the GMLAN with a hand built device. The GMLAN is pretty simple. There also is a chip available from Scantool.net that makes the job a LOT easier if you are trying to talk via a Arduino or other type of computer.

    If you decide to go with an Arduino or similar you could setup a box that is setup to handle what you want to and also have it do some ODBII diagnostics for you as well as whatever else you want to do with it.

    Rodney

  9. #59
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    The components bcm and transmission computer are from an 06 silverado 2500HD with a duramax and allison transmission. They are not in the truck, but I do have the gmlan from the trans computer hooked up to the obd2 connector so it can be tuned with efi live. The tcm is also hooked up to the bcm via the class 2 serial data line. The bcm also has a connection to the obd 2 data connector.
    Trying to use aduino to get the hex code from the class 2 data line. Then use arduino to emulate the same signal to enable/disable tow haul mode.
    Im a car guy, with descent electronics knowledge. I can make the hardware work but a novice when it comes to programing or coding.

  10. #60
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    So your BCM and Trans computer are from an 06 3/4 ton diesel. Are you saying BCM when you mean ECM?

    Also what year is your truck? I believe 2006 is when GM changed the databuses somewhat and you now have a high speed CANBUS to go along with the low speed GMLAN.

    From what I gather, in 2003 it is looking more and more like they only had the GMLAN and it was at 10.3k baud. In 2006 it looks like they have a CAN bus that runs at 500k baud and a GMLAN bus that runs at 33k baud so they are not really compatible.

    SO first I would say you need to make sure the control unit needs to be from the same year to make it a little easier. You will likely either need to make your truck think it still has the original engine/trans in it with some sort of translator between the units or have someone reprogram your computers to fit in with the new host truck. Because everything is so tied together I believe your best bet is to find a place that does the reprogramming you need. I know they are out there... I have seen where there are trans shops that will retro fit just about any transmission.

    Another option... Here is a link to a guy that put a Duramax into his Avalanche:

    http://chevyavalanchefanclub.com/caf...,125691.0.html

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