Thread: OBD2 / Elm327 Developers - Please Aid

ill try to explain, say your car is KWP2000 ( thats the protocol for engine management ) as said before and works in ASCII or OBDII/EOBD now CAN bus its a protocol on its own so basicly ELM327 has 2 interfaces built into it and works best with USB2 because its a faster network but you can use the serial side but as said by another member it has to be buffered because serial is too slow thats why is has the XON/XOFF and has to be turned on in your device manager if your going to use serial connection,
hopefully this will shed a little light on the subject as this is where people tend to go wrong

Originally Posted by techbod

ill try to explain, say your car is KWP2000 ( thats the protocol for engine management ) as said before and works in ASCII or OBDII/EOBD now CAN bus its a protocol on its own so basicly ELM327 has 2 interfaces built into it and works best with USB2 because its a faster network but you can use the serial side but as said by another member it has to be buffered because serial is too slow thats why is has the XON/XOFF and has to be turned on in your device manager if your going to use serial connection,
hopefully this will shed a little light on the subject as this is where people tend to go wrong

That, I already know. What I need to know is how to initialize the ELM, in this case, for both interfaces. Basically a brief description of the ELM327 communication protocol.

The ELM327 datasheet lists all the commands necessary to select the protocol, issue commands and receive data. The ELM can only operate using one protocol at a time, unlike a lot of other tools.

As for a library, the only thing that comes close is the source the Scantool software at scantool.net.

Cardix is an SDK that was adding support for ELM at some point. At the moment I think it's primarily J2534.


Lukeyson

That I know too. The problem is that the command table on the ELM327 ref sheet does not tell how they are to be used (i.e. order for initialization, how data is retrieved, etc), it only lists the commands.

This is in perfect timing for me, I'd like to know how to use the ELM327 as well.

Apparently Scantool.net is open source so you can check out how they do it, however it's much much simpler to just follow some instructions and send the commands rather than decode someones source in a different language.

If you haven't already got it, as Lukeyson pointed out the datasheet from Elm Electronics is a good place to start for the Elm AT commands, but to know what to send and how to interpret the responses you'll need a copy of SAE J1939 or ISO 150310-5 to proceed further.

Graham McKechnie
GLM Software
www.glmsoftware.com

I'm working on a c++ OBD2 (ISO) interface library, however its based off of the ELM from here: http://www.obdpros.com/ Not sure if that is compatable with what you are working with, but I can port it to c# when I'm finished if it is.

im an old tech and these new systems intrigue me because the dealers are screwing us in costs for very basic none fault codes thinking we are dumb now im starting to learn more since I retired and using it to help those who cant afford dealer prices,
im no programmer so just got basic knowledge in this area but when it comes to diagnosing and fixing cars that's my area of expertise so its a need to know thing with me in fact I think I'm getting obsessed with it lol ( your never too old to learn ) my father told me that many years ago and its taken over my life "not much else to do at my age" but it keeps my mind busy so I don't turn into an old fossil, I glad to see so much enthusiasm on this subject it really helps

Actually, if you're at the point of issuing commands to get data out of modules, you might be beyond the mere scope of the tools and into the realms of the standards.

J1979 - is the first standard - it's across all cars but only gets basic stuff out of the PCM.
J2190 - is very bloody useful, and outlines the standards by which modules can be manipulated.

14229-1 would be useful - Universal Diagnostics. ie diagnostics on your protocol
15765-3 is also useful - diagnostics on CAN.

These are a bit of a re-hash on J2190, but are still useful as well.

As for the rest - well, you have to get through the big black door. All of the data in these modules is considered prioritary and confidential, so is not released to the public. But you can subscribe to ETI if you're rich and can access vendor data that way. If you want to write commerical software you have to licence the proprietary data from a manufacturer - and that ain't cheap either. Just ask Brian from PalmerPerformance!


Lukeyson