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Thread: Relationship Between two Hex strings...

  1. #1
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    Question Relationship Between two Hex strings...

    Hi All!

    I'm trying to make a .NET based application for ELM327 trouble code scanning device. Most of my app code is done. however, I am stuck at one point. And I need someone to help me decode two hex strings to find a relationship between them.

    I have logged some communication between ECU and a trouble code scanner for carrying out car's fuel pressure test. However there is one message (that is sent from the user side) that keeps on changing each time which is dependent upon the last message received from the ECU which is also varying every time.
    I'm posting different responses from logged data for carrying out fuel pressure test at different times.

    Code:
    RECEIVED (07E8)			     SEND (07E0)
    05 67 03 0C 17 6A 00 00	     05 27 04 8F 45 37 00 00
    05 67 03 0C DB 68 00 00	     05 27 04 B0 70 6B 00 00
    05 67 03 10 3B 87 00 00	     05 27 04 3B BC 10 00 00
    05 67 03 12 CC E7 00 00	     05 27 04 5A 50 5B 00 00
    05 67 03 13 A4 88 00 00	     05 27 04 34 E7 63 00 00
    05 67 03 15 D9 CB 00 00	     05 27 04 5D 76 7D 00 00
    05 67 03 1A 2F 05 00 00	     05 27 04 57 81 33 00 00
    05 67 03 1B 45 AE 00 00	     05 27 04 E8 10 E7 00 00
    05 67 03 29 BC B3 00 00	     05 27 04 85 65 10 00 00
    05 67 03 31 09 97 00 00	     05 27 04 E1 FB A6 00 00
    05 67 03 32 C5 6B 00 00	     05 27 04 D1 EC 83 00 00
    05 67 03 33 1E 9E 00 00	     05 27 04 7A A4 AF 00 00
    05 67 03 3A F6 2F 00 00	     05 27 04 71 26 98 00 00
    05 67 03 3B 75 AB 00 00	     05 27 04 E9 76 0C 00 00
    05 67 03 3E 50 51 00 00	     05 27 04 59 2B 67 00 00
    05 67 03 3F D9 94 00 00	     05 27 04 91 2B D3 00 00
    05 67 03 42 58 A9 00 00	     05 27 04 19 E7 CB 00 00
    05 67 03 43 F9 A0 00 00	     05 27 04 55 81 ED 00 00
    05 67 03 48 82 DD 00 00	     05 27 04 F3 2D 41 00 00
    05 67 03 4E 25 DE 00 00	     05 27 04 DE F2 99 00 00
    05 67 03 51 40 DE 00 00	     05 27 04 DB B6 DF 00 00
    as it can be seen 3 bytes are always changing with each test, both, in the message received from the ECU, and the one sent back to the ECU from the diagnostic scanner. Can anyone help me trying to figure out relationship between these two strings?

    P.S: The messages under RECEIVED column come in reply to a command "02 27 03". currently I've stored about 70 logs in a database. my program keeps on sending the command "02 27 03" until it gets a reply that I already have in the database. In that case the fuel pressure test starts successfully. but it often takes hours because there exist more than 16 million combinations for 3 byte data...
    Last edited by Awais Niazi; 08-17-2013 at 06:06 PM.

  2. #2
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    To help you we need to know what kind of vehicle and the year.

    If it is new enough to be ODBII the commands are pretty standard and should help you out dramatically.

    If you have an odbii vehicle then you can search for ODBII codes pretty easily.

  3. #3
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    Quote Originally Posted by redheadedrod View Post
    To help you we need to know what kind of vehicle and the year.

    If it is new enough to be ODBII the commands are pretty standard and should help you out dramatically.

    If you have an odbii vehicle then you can search for ODBII codes pretty easily.
    thanks for the quick reply. well sorry my bad I should have mentioned the vehicle. its Land Rover Defender model 2007 (11 bit CAN)

  4. #4
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    and yes indeed it is OBD-II Standard vehicle...

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