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can't understand basics.. how the scan tools work?

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  • can't understand basics.. how the scan tools work?

    I have just started researching the odbii part of my carpc project, and I am confused about some of the basics...

    ODBii provides signals that are standardized, but the data transfer method (the bits on the wire.. maybe call it the protocol?) are different based upon manufacturer choice. At least this is what I got from reading the sticky. So you need a device to go between the interface of the car and the serial port on your 'puter that can handle the specific transfer method used by that car manufacturer I gather.

    If I got this much right, then it seems to me that you now have all of the data sent to your serial port, which you could pick up and program into a display GUI.

    So why is it that these provide different output data? IE some packages can read some functions out of the system but not others? It seems that you could read any codes you would want out of the ODBii system. Once you had used one of these boxes to convert the data to serial it should just be a matter of pulling the data out you want and displaying it with software written to make sense of the output.

    I must be confused here....

  • #2
    thats what i got out of that too, but didnt think about it anymore after that, thanks for brinign that up, im interested now too

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    • #3
      Roger, you don't have to reply to every thread. SLushieken, a lot of the bottlenek in reading data is in the units that you buy. This is mainly because, as you said, differen't manufactureres use different protocols, so the basic tools, or at least my assumptions would lead me to conclude that they, are constructed to fit a large range of vehichles, and so it may not include some specific features.
      My Carputer! (More Car Pics at the end)
      2 Kicker Comp 10"
      Epia M-9000, 256 MB DDR, 120 Gig HD
      Lilliput 7" VGA Touchscreen
      Check it out?!

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      • #4
        aww why not (cries and hides under bed) as of recent its become one of my favs, sneaks another post in... j/k

        Do manufacuteres themselves produce these readers? I know i found a online manual of my ford vehicle, and its very conveint for any wiring, if these were somehow compatible that would be the best diagnostic tool i've ever seen!

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        • #5
          Buy a universal scan tool like Autoenginuity's and you won't have to worry about manufacturer specific protocols. Otherwise, OBD-2 is a standard and the tool fits all cars that are 1996 and up. Some 2004s now use CAN though.

          Say you buy the universal tool.
          Plug it into the car's OBD-2 port.
          Start the car.
          Turn on the software.
          Wait for the software to connect to the car.
          Bang. Pick all the data options you want, including clearing check engines... etc.
          You can now monitor the car live and drive away logging data such as fuel trims, rpms vs. speed, O2 sensors, Mass Air Flow, Air intake temp (for those with CAIs...)... etc. If it's not related to the ecu, you can't monitor it.

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          • #6
            Originally posted by RogerWilco
            aww why not (cries and hides under bed) as of recent its become one of my favs, sneaks another post in... j/k

            Do manufacuteres themselves produce these readers? I know i found a online manual of my ford vehicle, and its very conveint for any wiring, if these were somehow compatible that would be the best diagnostic tool i've ever seen!
            Ya know roger... theres this website that you would probably find useful and maybe even get as excited about as this one!! Almost every question/response i have seen you post here can be found on this website...

            are you ready??


















            www.google.com


            Yay!! for google!!
            The Ultimate CBCC?? (Clean Black Car Club)

            Click here for the Truth

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            • #7
              Ya know roger... theres this website that you would probably find useful and maybe even get as excited about as this one!! Almost every question/response i have seen you post here can be found on this website...

              are you ready??
              How about you search google, right now and find me the online manual i have of my ford explorer.
              Whats that ? you cant find it?
              so im guessing it doesnt exist right?
              .

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              • #8
                Are you 10 or 13?

                just curious.
                The Ultimate CBCC?? (Clean Black Car Club)

                Click here for the Truth

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                • #9
                  thats a nice Mitsubishi Eclipse GS?
                  are you 10?

                  Comment


                  • #10
                    "Do manufacuteres themselves produce these readers? I know i found a online manual of my ford vehicle, and its very conveint for any wiring, if these were somehow compatible that would be the best diagnostic tool i've ever seen!"

                    yes, most of the OEMs produce the readers. Some hire the hardware portion out, but stay very close to the development and ongoing validation testing. Also, most OEMs also provide service manuals online too, to comply with federal requirements. Chrysler's is www.techauthority.com. I believe ETI's website lists all the major OEMs websites.

                    The diagnostic tools and the factory owner's manuals / diagnostic manuals are closely related to make it more efficient for a technician to repair the vehicle with the appropriate tools (like a scan tool).

                    The federal OBD2 generic specification was to make it easier for a non OEM scan tool manufacturer a way to produce tools that could be sold to the service aftermarket. It covers the spec that the vehicle should respond to. This is what the scan tool hardware needs to know to communicate with the vehicle. The communication between scan tool hardware and PC is not specified and can be proprietary to the scan tool hardware company. Many aftermarket and hobbyiest scan tool companies post their API so that other software developers can use the scan tool hardware. Some do not, because the market is not very big or lucrative yet to support the API and all the support calls that can come in by hobbiests trying to use the hardware.

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                    • #11
                      Originally posted by DavidL
                      The federal OBD2 generic specification was to make it easier for a non OEM scan tool manufacturer a way to produce tools that could be sold to the service aftermarket. It covers the spec that the vehicle should respond to. This is what the scan tool hardware needs to know to communicate with the vehicle. The communication between scan tool hardware and PC is not specified and can be proprietary to the scan tool hardware company. Many aftermarket and hobbyiest scan tool companies post their API so that other software developers can use the scan tool hardware. Some do not, because the market is not very big or lucrative yet to support the API and all the support calls that can come in by hobbiests trying to use the hardware.
                      OK wanted to point this out as pretty reasonable. Then are you saying that I could buy one the packages that comes with the source etc. and possibly (possibly - like an inifinite number of monkeys and trypewriters could possibly write the collected works of Shakespeare) write an app that would give me all available computer data? Even the chassis subsystem messages?

                      And not to muddy the waters further but does this work the same for systems that you can use to provide input to the ODBii system?

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                      • #12
                        Well, like noted in several prior posts, there are multiple layers of data that is accesible to/from the vehicle. OBD2 covers the set that is useful for diagnostics, enhanced data is for rest of information that is not specified by the government regulation. Enhanced is vehicle specific. The OEMs usually publish the access methodology even to enhanced, but are not required to. The best source for this data (if you are a hardware / software developer) is via ETI industry group. This is not a trivial support matter. It takes much effort to maintain the support for just one vehicle, never mind the large variety of vehicles that are common or exist.

                        The best way is to use a commercial product and program to that product's API and let the scan tool program deal with the issues of communicating and translating the data into human speak.

                        There are also multiple modules on each vehicle that provide other services. Transmission, then Body, then Antilock, then Airbag, then key /entry modules, etc. from most popular data to less popular (from a diagnostic support perspective).

                        Most of the controllers also have bi-directional support to aid in diagnostics. For example, turn the fan relay on, move the idle up/down (AIS motor), turn the A/C compressor relay on, etc.

                        Native programming of the ECU (the "Flash") is where settings like ignition timing, fuel control (including limiter functions) are programmed and are not resettable via the diagnostic connector without changing the core coding. This is usually encrypted for security and requires significant expertise to modify.

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                        • #13
                          DavidL-

                          Thanks for the explanation! You must have read my mind...

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                          • #14
                            DaivdL
                            Thanks, that was very helpful, one more question though.
                            So your saying that the ODBII, is bi-direcional? everyone else i've spoken to has said that its simply for taking readings. please correct me if i've misread something.

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                            • #15
                              Depends on the car. For example, Ford will allow you to "active command" certain features, like the cooling fan, imrc, evap solenoids, solenoids in the trans, ect. It is used for diagnostic, so only those features needed are allowed. Also, the PCM is reflashable when over 15 volts is applied to a pin on the dlc connector. I wont go into which one cause if you dont have the right tool (WDS is the proper scan tool) you can really let the smoke out of the box.
                              2005 Ford Focus ST

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