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Thread: General help needed with OBD II protocols

  1. #1
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    General help needed with OBD II protocols

    Hi,

    This isn't Car-PC related but rather protocol related... I've been reading this forum and see there's many people here with in-depth knowledge of the various protocols used through the OBD II interface. I'm hoping that someone will be able to help me out since i haven't been able to find any information.

    I purchased a scanguage II recently basically for its DTC reading/clearing functions and guage data. Their website advertised being able to add custom gauges, and i wanted to monitor my transmission temperature sensor.

    They only provided trans temp programming codes for VPW and CANxx vehicles. My scanguage says it's using protocol KWPf. I'm trying to find information on this protocol so i can possibly figure out a way to get this gauge working but i'm coming up with nothing. scanguage support was less than helpful suggesting i try the ISO codes for VW (didn't work)

    A friend has an ELM327 that i can borrow to probe the OBD II port but i don't really know where to start.

    Can anyone point me to some information on this protocol, and maybe give me some pointers on where to start? links to relevant reading material are appreciated, i'm not expecting to be spoon-fed but really don't know where to start with figuring this out.

    If it's relevant the vehicle in question is an 05 saturn Vue (GM), but the powertrain is a honda V6 w 5 speed AT... That's not custom, that's how these came from the factory.

  2. #2
    Constant Bitrate joeyoravec's Avatar
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    Quote Originally Posted by kevin1162 View Post
    They only provided trans temp programming codes for VPW and CANxx vehicles. My scanguage says it's using protocol KWPf.
    I think you're looking at the problem at the wrong layer. When you talk about CAN or VPW or KWP you're basically talking about the network wire (sort of like ethernet). Just because a vehicle uses X doesn't mean it has anything in common with another vehicle that uses X. For example reading trans temp on a Volkswagen has absolutely nothing in common with a GM even if they both use CAN. Or even reading on a pre-2008 Ford has very little in common with a post-2008 Ford even if they both use CAN.

    Quote Originally Posted by kevin1162 View Post
    If it's relevant the vehicle in question is an 05 saturn Vue (GM), but the powertrain is a honda V6 w 5 speed AT... That's not custom, that's how these came from the factory.
    There's the real problem. Like any good bureaucracy, GM has a corporate standard and they follow it for "most" vehicles in the family. However KWP vehicles (Saturn, some Cadillac, Pontiac Vibe, etc) are almost always using an outsourced powertrain and the diagnostics will be very different. All I could recommend is to try reading it with the dealer tool, monitor the network and see what happens.

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    I understand what you mean... The reason my post was worded the way it was is because the scanguage xguage command sheet provides enhanced data commands which are supposed to be universal for each manufacturer dependent on the protocol.

    I.e. GM VPW vehicles send send command 6C10F122194001 to receive trans temp data where GM CANSF vehicles send 07E022194001...according to their data sheet.

    no years or anything are specified so i figured that each manufacturer would have a set of 'universal' commands. Even though they don't i was secretly hoping there would be a way to figure this out without using the GM Tech II since it's near impossible to get your hands on one unless you buy it.

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    Constant Bitrate joeyoravec's Avatar
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    Quote Originally Posted by kevin1162 View Post
    I.e. GM VPW vehicles send send command 6C10F122194001 to receive trans temp data where GM CANSF vehicles send 07E022194001...according to their data sheet.
    There's some structure to the madness. I can try to break it down, it's actually kind of similar:
    VPW:
    Header: 6C = Type of request, 10 = destination (ecm), F1 = source (obd2 tool)
    Request: 22 = Read Data by parameter identifier
    Argument: 1940 = Trans Fluid Temp

    CAN:
    Header: 7E0 = address (obd2 tool to ecm)
    Request: 22 = Read Data by parameter identifier
    Argument: 1940 = Trans Fluid Temp
    So sure in the ideal case GM followed their own standard, but across enough vehicles you start to see the problem. Like why ask to the engine controller when the trans is usually what knows fluid temperature. And not all vehicles support command 22 to read by identifier. And not all vehicles are going to call it parameter 1940. Etc.. It's not quite as universal as that user manual might lead you to believe. Especially for your car which is outside the mainstream.

    Quote Originally Posted by kevin1162 View Post
    no years or anything are specified so i figured that each manufacturer would have a set of 'universal' commands. Even though they don't i was secretly hoping there would be a way to figure this out without using the GM Tech II since it's near impossible to get your hands on one unless you buy it.
    Tech2 has been replaced by the MDI, and it seems like they're dropping features from the tech2 especially on KWP vehicles. I don't blame them, it must be a nightmare to support the few vehicles that work differently. So you might do better finding an MDI and TIS.

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    This is starting to make sense...

    Is there anywhere i can find information on things like

    -the packet-structure of the different protocols
    -parameter identifiers
    -arguments


    So you might do better finding an MDI and TIS
    What do those acronyms stand for?

    it seems like they're dropping features from the tech2 especially on KWP vehicles
    Can i assume then that KWPf is just a minor variation on the KWP2000 protocol? What's different between the two?

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    Constant Bitrate joeyoravec's Avatar
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    Quote Originally Posted by kevin1162 View Post
    Is there anywhere i can find information on things...
    SAE HS-3000 is the collection of standards for passenger vehicles. It contains good background knowledge but the details come straight from the automaker, and GM charges something like $50k for a license which is insane

    MDI (Multiple Diagnostic Interface) is the tech2 successor, except this time there's no screen and it's intended to use with a laptop. Here's a PDF with slightly more info: http://boschdiagnostictools.com/stor.../mdi-tech2.pdf

    Quote Originally Posted by kevin1162 View Post
    Can i assume then that KWPf is just a minor variation on the KWP2000 protocol? What's different between the two?
    I don't know the term kwpf. I looked at the scangauge docs and I see a lot of other acronyms that they seem to have invented. It probably means something to them, but not to me.

  7. #7
    VENDOR - ScanTool Vitaliy's Avatar
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    "KWPf" probably means KWP w/ fast init.
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    AE HS-3000 is the collection of standards for passenger vehicles. It contains good background knowledge but the details come straight from the automaker, and GM charges something like $50k for a license which is insane
    too rich for my blood lol

    MDI (Multiple Diagnostic Interface) is the tech2 successor, except this time there's no screen and it's intended to use with a laptop. Here's a PDF with slightly more info: http://boschdiagnostictools.com/stor.../mdi-tech2.pdf
    Yeah i found that out after posting, because of my model year the only advantage that has over the Tech2 for me (that i can see anyway) is being quicker at flashing the ECU... But the cost of that and then a subscription to TIS just to find out what the address and PID are that i need isn't really economical (neither is a tech2).

    "KWPf" probably means KWP w/ fast init.
    As far as i can tell you are correct... Everything i could find is saying that my car utilizes ISO14230-4.

    Like why ask to the engine controller when the trans is usually what knows fluid temperature
    So i started to think about this after learning more about the data structure of the command that i'm trying to send (priority, destination, source, etc)... I'm probably looking at one of these scenarios:

    - PID for trans-fluid temp is incorrect
    - destination address is incorrect (need TCM not ECM)
    - This data not present within the KWP serial stream

    Can anyone speculate which one is most likely? I know that my vehicle has a trans temp sensor and that it does output a variable value, not just on/off. But I looked at the pinout of my DLC through alldata and pin 2 is for 'class 2 data'. wtf is class 2 data and is it likely that my trans temp info would be transmitted on this bus instead? Pretty sure that the scanguage is only looking at the KWP data lines.

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    Constant Bitrate joeyoravec's Avatar
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    Quote Originally Posted by kevin1162 View Post
    But I looked at the pinout of my DLC through alldata and pin 2 is for 'class 2 data'. wtf is class 2 data and is it likely that my trans temp info would be transmitted on this bus instead?
    Class2 is GM diagnostics on a J1850VPW network. Anything's possible. Maybe it has a split architecture where some modules are on VPW some on KWP. Maybe they have an X-to-VPW gateway for compatibility with GM diagnostic tools. Or maybe it's on the diagram but the wire is unused. Hard to say, you'd have to try it out.

    Quote Originally Posted by kevin1162 View Post
    Can anyone speculate which one is most likely? I know that my vehicle has a trans temp sensor and that it does output a variable value, not just on/off.
    Add to that list "doesn't do command 22" for reading data. Your header is definitely wrong for iso14230, but my guess is that your car has radically different diagnostics. For example the vibe (on kwp) you have to send totally different commands as if it was a toyota. Wouldn't surprise me if saturn decided to think different and do their own thing too.

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    Your header is definitely wrong for iso14230
    I never thought of that... I found a document from linear-logic about the the header-structure and it states that the first 3 bytes of the command are stuctured the same for VPW, ISO, and KWP.

    It's probably because i don't know exact terms to search for but i can't find anything that defines the structure of a KWP command.

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