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Thread: BUFFER FULL ELM327 with mode 06 request

  1. #1
    Low Bitrate remus08's Avatar
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    BUFFER FULL ELM327 with mode 06 request

    Hi all,

    I've recently have a buffer full message from an ELM327 on this request

    Code:
    733.066927 > 0631
    733.156641 < 7E81040463186304444
    733.181443 < 7E821351E7000319630
    733.232047 < 7E822004C00000AF031
    733.287331 < 7E82397300090000006
    733.343711 < 7E82440319A3000C600
    733.399856 < 7E825002AF8319B3000
    733.400217 < 7E8260A00000A28319C
    733.400536 < 7E82730015200002AF8
    733.400852 < 7E828319D30000A0000
    733.407043 < 7E8290A28
    733.427031 < BUFFERFULL
    First question: I knwon that means this error but I don't understand why there so many datas in the response?

    Second question: If we look at PCI length on the FF CAN. it indicate a legnth of 40h (64 bytes) and the ELM327 datasheet said (page 52):

    The ELM327 provides a 256 byte internal RS232 transmit buffer...
    Thanks in advance!

  2. #2
    VENDOR - ScanTool Vitaliy's Avatar
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    This is a known issue with the ELM327.

    The problem is, the 256 bytes of buffer are on the UART side. CAN Tx/Rx buffers can hold a combined total of six CAN messages.

    OBDLink overcomes this problem by dynamically allocating a much larger buffer, so you will never see BUFFER FULL messages except at very low baud rates.

    You may be able to solve the problem in your case, by cranking up the baud rate up to 500 kbps.

    Vitaliy
    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.

  3. #3
    Low Bitrate remus08's Avatar
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    Thanks Vitaliy,

    Actaully, RS baud rate setup is 9600 and the chip is an ELM327 v1.5a (I guess a very poor fake). I'm gonna test with higher baud rate.

    Is someone is able to explain me how to "decipher" the message's data? Usually mode 6 response have got 10 bytes...

  4. #4
    VENDOR - ScanTool Vitaliy's Avatar
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    Do you not have a copy of SAE J1979? For TID > $0C the meaning is manufacturer specific.
    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.

  5. #5
    What can I say? I like serial. Curiosity's Avatar
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    Quote Originally Posted by remus08 View Post
    the chip is an ELM327 v1.5a (I guess a very poor fake)
    Assume it's v1.2 or earlier firmware with the version number hacked, then everything will make sense.

  6. #6
    Low Bitrate remus08's Avatar
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    Ok I think I've understood
    So we can parse the response this way

    Code:
    46
    31 86 30 4444 351E 7000
    31 96 30 004C 0000 0AF0
    31 97 30 0090 0000 06440
    31 9A 30 00C6 0000 2AF8
    31 9B 30 000A 0000 0A28
    31 9C 30 0152 0000 2AF8
    31 9D 30 000A 0000 0A28
    I didn't know that one OBDMID can support multiple TIDs, that why I was confused but that's my fault because the SAEJ1979 show an example with O2S bank1 sensor1.
    Even I don't know the meaning of the TIDs (86, 96, 97, 9A, 9B, 9C, 9D), I'm able to say they are all completed

    Thanks for your help

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