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Thread: How to turn on "show me everything on the bus, please" mode

  1. #1
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    How to turn on "show me everything on the bus, please" mode

    I have a Scantool.net OBDLink SX, which I presume is based on the STN1110. I can connect just fine using either the supplied OBDWiz or a terminal program.

    My problem is I'd like to monitor traffic to sniff out non-standard PIDs, but I'm not having any luck. Maybe this tool/chip just can't do it, but I've done it with an old original ELM327 some time ago, so unless I've forgotten an important step, something is different.

    Can anyone tell me how to turn off filtering so I can see the various modules talking to one another?

    Many thanks!
    Dave

  2. #2
    SuperMod - OBDII GPS Logger forum
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    You may be talking about ATMA?

    Gary (-;
    OBDGPSLogger, for logging OBDII and/or GPS data
    OBDSim, an OBDII/ELM327 software simulator
    mp3car forums: obdgpslogger, obdsim

  3. #3
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    I am indeed. On an '03 BMW M3 I got -no- response from ATMA. On a Cadillac Escalade, I got about 10 lines of data and then "BUFFER FULL". There are a number of posts related to this but nothing in the "Here's how you set the baud rate so you can capture a few seconds worth of data".

    So, if anyone knows how (and I'm fine with ODBWiz or TerraTerm, Hyperterm, whatever) to get it to do a decent dump, please let me know!

    My first shot was "STBR 460800" which did appear to change the baud rate, but when I set the terminal program to 460800 I could only get garbage, so I'm missing something!

    Thanks,
    Dave

  4. #4
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    Modifying the baudrate, there's a whole protocol around doing it successfully [the ELM327 datasheet explains in detail]. The problem is that it's borderline impossible to do manually; clearly it was intended to be trivial to do in code, and it is.

    Make sure you upgrade your scantool with the latest firmware. The current default baudrate is 115200 which should be acceptable.

    You could set the CAN filtering [again, the elm327 datasheet covers it] to only search on ECUs you specifically want. That's probably the first,best way to cut traffic and noise to what you want.

    Hitting a key after "ATMA" cancels it. Make sure you didn't do that accidentally in the M3. Otherwise, perhaps the M3 just isn't very chatty?

    Gary (-;
    OBDGPSLogger, for logging OBDII and/or GPS data
    OBDSim, an OBDII/ELM327 software simulator
    mp3car forums: obdgpslogger, obdsim

  5. #5
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    I did read the datasheet, and I think you're confirming what I suspected: you only have about 50ms to 'confirm' that the new baud rate is OK, and that's pretty hard to do (ie: change the serial port settings) in a comm program!

    Since I'm trying to narrow down and locate a particular command on a particular module (as a test, door lock) I'm not sure how to proceed, because there's too much data to run ATMA unfiltered and yet I don't know the module's CAN BUS ID (or address) to filter!

    I don't suppose there's a registry or database of module IDs anywhere?

  6. #6
    SuperMod - OBDII GPS Logger forum
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    You could change that 50ms using ATST, if you like. But yeah, the default 50ms isn't easy to work with

    Turn on headers [ATH1] and run 0100. That'll be a good start, as it'll give you a list of ECUs to start from.

    Gary (-;
    OBDGPSLogger, for logging OBDII and/or GPS data
    OBDSim, an OBDII/ELM327 software simulator
    mp3car forums: obdgpslogger, obdsim

  7. #7
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    If the same tool worked on an Escalade, but doesn't work on an M3 and you were able to get OBD data from the M3(right protocol), the BMW may have a diagnostic bus connected to a gateway that has no traffic except what a scan tool generates.

  8. #8
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    I described an easier way to switch baud rate on OBDLink, and a better method for avoiding BUFFER OVERFLOW errors, in this thread:

    https://www.scantool.net/forum/index...19371#msg19371
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
    — Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

    You cannot send me a private message using this forum. Use my email instead: vitaliy[@]scantool.net.

  9. #9
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    Quote Originally Posted by DAVEPL1968 View Post
    I have a Scantool.net OBDLink SX, which I presume is based on the STN1110. I can connect just fine using either the supplied OBDWiz or a terminal program.

    My problem is I'd like to monitor traffic to sniff out non-standard PIDs, but I'm not having any luck. Maybe this tool/chip just can't do it, but I've done it with an old original ELM327 some time ago, so unless I've forgotten an important step, something is different.

    Can anyone tell me how to turn off filtering so I can see the various modules talking to one another?

    Many thanks!
    Dave
    Dave, the truth is that the elm chip wasn't really designed to allow an unfiltered can bus to be viewed. There seems to be some work arounds, but thats just what they are.. Work arounds.

    If you are serious about this get a CAN to USB converter. There are several on the market. valueCAN, CANUSB, or the drew tech device (forget the name).

    If you need to use elm, then remember that the data rate of the can bus is likely at 500 kbs and the comms back to the pc is 115.2 kbps. So when the data throughput on CAN is high the link back to the pc is a bottleneck that results in the can buffer not able to be serviced fast enough. Thus buffer overflow.

    Good luck.
    Hack Your Car
    www.CanBusHack.com

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    Did you know that I had two IDs on this web site.. Neither did I (well I forgot).. So I guess I go by both names: chewtoy and chewwtoy.. what's next?
    Hack your car's CAN BUS at www.canbushack.com

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