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Thread: articles on hacking your vehicle bus

  1. #11
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    So if you want to hook to the Single wire protocols I am assuming you connect the -Can to ground and +Can to the data line. Is that correct?

    Rodney

  2. #12
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    Quote Originally Posted by redheadedrod View Post
    So if you want to hook to the Single wire protocols I am assuming you connect the -Can to ground and +Can to the data line. Is that correct?

    Rodney

    Quote Originally Posted by redheadedrod View Post
    So if you want to hook to the Single wire protocols I am assuming you connect the -Can to ground and +Can to the data line. Is that correct?

    Rodney
    which protocol exactly?

    mine is Chrysler J1850 VPW which is a single wire so i had to hook up as follows:

    [16] to +12v
    [4] & [5] to ground
    [2] to the Chrysler PCI data line



    the above picture is the port on the vehicle, i'm actually talking about the pins on the OBD2 adapter itself, which is the mirror image of that i guess

  3. #13
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    I guess based on this link:

    http://www.archivedsites.com/techcon...n_feb_09_F.pdf

    I am using pin #2 to communicate with it. Not sure how to go from there..
    By your display it looks like I would need to tie into 2 and 10 but they only show #2.

    And I am not sure how you actually connect to it that way.

    I also just found this video that goes into detail:

    https://www.youtube.com/watch?v=98h9qULPRus

    Rodney
    Last edited by redheadedrod; 08-12-2014 at 02:38 PM.

  4. #14
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    Quote Originally Posted by redheadedrod View Post
    I guess based on this link:

    http://www.archivedsites.com/techcon...n_feb_09_F.pdf

    I am using pin #2 to communicate with it. Not sure how to go from there..
    By your display it looks like I would need to tie into 2 and 10 but they only show #2.

    And I am not sure how you actually connect to it that way.

    I also just found this video that goes into detail:

    https://www.youtube.com/watch?v=98h9qULPRus

    Rodney

    interesting, so on quick glance it looks like some GM vehicles speak a CAN protocol on pins 6/14 and that's the default OBD2 interface which can connect to engine or interior systems. however, they also still support the older J1850 VPW (one-wire) protocol on pin 2 (what GM refers to as "Class 2"). that Class 2 interface on pin 2 might be limited to interior systems depending on how exactly that BCM gateway works, not sure.

    so theoretically, if you have a vehicle configured like the PDF shows (i'm not sure the year range on that) - then you should be able to just plug right into the diagnostic port and either:

    - set the protocol to J1850 VPW (Class 2) using command ATSP2, and then use traditional commands like ATMA to see bus traffic. this would be very much like what i'm doing in my Jeep.
    - OR set the protocol to the correct CAN one (or maybe AUTO will choose the right one), and then you'll need to explore more about what AT commands are needed to interact with the CAN system as it's more complex and i'm not up on CAN yet.

    i don't see a need to splice into any wiring really.
    Last edited by theksmith; 08-12-2014 at 03:24 PM.

  5. #15
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    @redheadedrod - i was doing more research into this general area and realized that in my previous post i failed to comprehend even close to a full picture of how GM vehicle networks can be setup. my current understanding is:


    - older GM vehicles (i think ~1995 to ~2004-ish) used the "Class 2" protocol for everything. it conforms to the OBDII spec ISO 9141 / SAE J1850 (the 10.4 kbps VPW single-wire variation). you should be able to use pin 2 on any standard ELM327 compatible OBD2 adapter to talk to this network (and of course pins 4&5 go to ground and pin 16 to +12v). you would issue the command ATSP2 to force to this protocol. for these models/years, i am unsure if hooking to pin 2 on the car's diagnostic port will provide an interface to only the diagnostic bus or if all buses are linked to it (or if there are even separate busses), you'd have to explore. 10.4kbps is a slow crawl and should be easy enough to decipher something out of if the bus isn't too saturated.


    - about 2004 GM started to use CAN protocols along with the Class 2 systems. they called their CAN protocols GMLAN, and they come in 2 flavors - high speed and low speed (GMLAN HS & GMLAN LS). technically they have a mid speed version too but i haven't seen anything about what might use it.

    -- the Class 2 bus was kept around for most interior items like doors, HVAC, some radio models, etc. - but only for a few years.

    -- for "not that old" cars the GMLAN LS bus augmented the Class 2 bus to do "other" interior stuff including the Heads-Up Display and certain radio versions. on newer cars (not sure the year), i the Class 2 bus is completely gone and all non-essential systems talk on this GMLAN LS bus. this LS bus is also known as Single Wire CAN or SW CAN, and as the name implies it's a bastard CAN standard that uses only one wire (SAE J2411). it moves at brisk walk of 33.33 kbps. it seems to be fairly standard that pin 1 on the car's diagnostic port gives access to this bus. however, it's not a standard OBDII thing, nor even a typical CAN implementation so talking to it requires a special transceiver usually not found in 99% of ELM327-compatible OBD2 dongles. however, ScanTool's OBDLink MX Bluetooth DOES have the right stuff and it's tied to pin 1 already: http://amzn.to/1vccPpn - i believe this product is using their stn1170 IC, but i cannot find in their datasheets what AT or ST commands are required to switch to this protocol, hopefully they would be forthcoming with the info as using this adapter would be a simple way to work with this bus. otherwise, the SparkFun CAN Bus shield is rumored to work with SW CAN though not really designed for it, and then there is the relatively new Raspberry PI CarberryPi shield project. of course you could go lower level and build your own circuit around any number of commercial transceiver ICs, but that's work.

    -- the GMLAN HS bus is used for powertrain and other important things that need near real-time interaction. it is a "normal" 2 wire CAN setup that conforms to the OBDII spec ISO 15765-4 / SAE J2284-3 (11 bit, 500 kbps warp speed). it will appear on the car's diagnostic port on the standard CAN pins 6 & 14 and most any OBD2 adapter should be able to talk to this (ATSP6 i think is the correct command). however, that might only get you diagnostic bus info... other pins may have additional GMLAN busses (check out the Chevy Volt for example...) however, note that only the latest versions of the ELM327 firmware (v2.1) include advanced CAN capabilities (and i don't know where to buy an OBD2 dongle with a genuine ELM327 IC in it). dongles based on ScanTool's stnXXXX ICs also look to have extra "ST" commands for dealing with CAN systems.


    sorry for the long post, but didn't want my previous one to mislead anyone. mainly it sounds like it depends on your model year whether you care about Class 2 on pin 2 or SW CAN on pin 1.
    Last edited by theksmith; 08-19-2014 at 07:34 AM.

  6. #16
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    Ok I guess I have to go back to the original question about the ELM or the scantool connectors. I actually have two Scantool devices at this time.

    For 1 wire connection do I just connect the Can- to Ground and the CAN+ to the SW connection?

    I have seen some postings of people saying this was the case but just want verification that I am on the right road. I have a scantool "chip" that is installed on a custom board built by a forum member. I will likely tie this into my main diagnostic bus and leave it there. I will likely try something different on the class 2 bus. Just trying to figure out what I need to do. I will be tying this permanently mounted board directly to the ODBII wires. This will still let me use my USB - ODBII cable if I desire or any other cable but will allow me a good connection to the bus for my computer.

    Thanks for the information you have presented so far. Saves me a lot of work once I get to it. Still ironing out some of my installation while moving and getting ready for the next semester.

    Rodney

  7. #17
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    Hey Rod the chip you have should be able to do what the MX does minus the Bluetooth of course. Check on scantools forum for the microobd200 chip is under developers its the same as the stn-1170. It might even be faster as in Driveline I continually stream obd2 data at 50hz or above SNO

  8. #18
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    Thanks sno

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