1997 E36 OBDII connectors

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  1. 1997 E36 OBDII connectors 
    #1
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    I have 1999 E46 with ELM327 OBDII cable and Scanmaster software. It works fine with the software. No fault codes etc. so I'm happy. When I use the same software with the 20 pin connector adapter on my 1997 E36 it does not connect. Any ideas why?

    Thanks for all your ideas and detailed response - but I take it that it is a no-no to try and get my E36 to connect.
    Last edited by Timz; 21-01-2011 at 18:41.
     
     

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    Yes. The E46 uses 1 wire for bi directional communications using the OBD2 ISO protocol.

    The E36 has separate Rx and Tx ports, and I don't think operates collision detection to prevent the units talking while they are receiving. There is also a third data line which may or may not be redundant. They are OBD2 compliant, however the modern adaptors use a single data line, so in theory you need a second TH3122 for the interface. I've not gotten to the bottom of it all yet, as to how off-the-shelf adaptors can be used on E36.
     
     

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    Timz (21-01-2011)

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    It does use more than one line, it has 2 separate K buses which are linked with a jumper cable in the ADS 20 pin plug, but the OBD2 code functionality in Euro cars is disabled.
    I have a feeling you may be right about the 2 wires/buses being used due to overcrowding of the data line.

    Any US car from 1996 will work with one of those readers, but the Euro spec wasn't fully OBD2, so missed out on post cat lambda sensors, the check engine light, and the easy OBD2 code reading.

    If the OBD2 code reading was disabled via the loom / wires used, it could be interesting, as there would be a way to make it function, but it seems that OBD2's ISO protocol was barred, and only BMWs "DS2" functions.
     
     

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    Very interesting slant that OBD2 messages are not supported in EU cars !

    I'v checked the wiring diagrams, and can't see a difference between post 1996 EU and US E36.

    The OBD2 functionality and whether it is disabled is interesting. OBD1 and OBD2 both use the same ISO9141 communications protocol, therefore all E36 should at least be able to accept the voltages and timing of ODB2 (haha probably). After all the M52 engine ECU is the same hardware and PN in US and EU models, as are 95% of the other ECUs.

    So is the message itself different for DS2? If so INPA allows you to select ADS as your interface and that should change the packet headers and footers and message content to suit EU cars.

    Assuming the vehicle and the adaptor are electrically compatible (full duplex on Rxd and Txd would probably be the pivoting feature), then INPA or SSS should be able to format the message to suit the EU models.
     
     

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    Timz (21-01-2011)

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    Quote Originally Posted by joylove View Post
    Very interesting slant that OBD2 messages are not supported in EU cars !

    I'v checked the wiring diagrams, and can't see a difference between post 1996 EU and US E36.

    The OBD2 functionality and whether it is disabled is interesting. OBD1 and OBD2 both use the same ISO9141 communications protocol, therefore all E36 should at least be able to accept the voltages and timing of ODB2 (haha probably). After all the M52 engine ECU is the same hardware and PN in US and EU models, as are 95% of the other ECUs.

    So is the message itself different for DS2? If so INPA allows you to select ADS as your interface and that should change the packet headers and footers and message content to suit EU cars.

    Assuming the vehicle and the adaptor are electrically compatible (full duplex on Rxd and Txd would probably be the pivoting feature), then INPA or SSS should be able to format the message to suit the EU models.
    DS2 might be a format of ISO, but it has a greater functionality. The exact messages / packet sniffing isn't something I've got into, but there are people making their own communication devices.
    You are correct that the M52 / Siemens ECU is the same hardware, but it would seem this functionality is enabled or disabled with the coding/SSS when the country code (or Vehicle Order- VO) is set.

    I believe all of BMWs diagnostics use their DS2 protocol, the headers would include the Bus Index (most modules will have a stick on them with the Index written on it)

    There will be a difference between the codes, as an OBD2 reader will just get a P code between 0-999 (and more for the BMW specific codes)
    http://endtuning.com/obdcodes.html

    On the flip side, the Siemens MS41 (328 M52 ecu) only has up to 255 codes
    http://endtuning.com/bmwcodes.html#MS41

    Obviously there will be 8 bit "slots" in the eeprom (I believe about 12 or 14) which can be filled by an 8 bit number.

    Because the OBD2 code reader does not need to be told it's talking to a BMW or MS series, it can't be taking the 8 bit number and translating it into one of the thousand plus P codes, there has to be a separate store of P and DS2 codes.
     
     

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    Having looked at the chatter and INPA logs, there is a lot of data passed beyond the fault code. Here you can see an INPA error log, it lists number of occurences, sporadic/constant fault, engine speed and so on. This will obviously be spread across a number of messages packetised in the relevant comms protocol. In this case it was a 1999 E46 over OBD2.




    I'm trying to say that potentially (depending on ECU model - age related) they are way beyond 256 'daughter' messages in scope, within the bounds of an 8 bit recorded fault code in the link.

    However, if the goal today is not to guess what the EU MS41 can do rather figure out how to talk DS2 to it on the cheap, I'm rather peturbed by finding this unsubstantiated tidbit here.
    Now I understand BMW only decided to institute OBD to conform to californian emission standards and did so rather reluctantly as you only get the bearest minimum on the OBD.

    I also believe E39's use the more 'in house' DS2 standard of communication with the car, and contain everything you could ever want to have a converstation to the car with, again through the OBD socket but using 9600,e,8,1 on a standard COM, instead of the 10400 n,8,1 but using the same K/L line wires.
    If the baud rate has been clobbered to 9600 from ISO9141 10.4k, this immediately means TH3122 ISO9141 compliant transceivers ICs (~£1 each at Farnell) are not compatible with DS2, and a few of them in full duplex would not be a suitable interface.

    A simple level translator would be the sort of thing needed.
     
     

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    Timz (21-01-2011)

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    Some of those timestamps are available to OBD2 systems under the name of "freeze frame data", and the frequency counter for errors is also 8 bit (recording up to 255 occurances)

    The error codes underneath some of those errors show 10 bytes, so it seems reasonable to think for each error, a 10 byte message is sent detailing the module, code, frequency, and freeze frame.

    I think I might have had some BMW diag training docs, but they are usually bare bones minimum to keep the techs up to speed of working the kit, rather than building their own ones.
     
     

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    I've seen a few schematics too, for 'OBD1' (Probably DS2) and most are based around level shifters, with no baud rate modifiers.
     
     

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    The main body is about using the DIS/GT1, but there is info on some changes to diag protocols, but not too in depth.
    Attached Files
     
     

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    Page 4 is a goldmine of info I was missing. Thanks.
     
     

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    Timz (21-01-2011)

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