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Thread: Multiple ECU responses

  1. #11
    Moderator - CarPC News Penzance's Avatar
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    Just as an aside, I found reading through this thread interesting. It applies specifically to Aussie Fords, but some of the insights made make it worth going through.

    Again, my apologies for sidetracking.

  2. #12
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    Quote Originally Posted by Vitaliy View Post
    Use the ATWM message to set up periodic keep-alives. It doesn't matter what you actually send, as long as it's a supported PID (like 01 0C).
    So the command would be ATWM 010C?

    But regarding the problem, do you have any idea what is causing it? I think that before I set the headers there is no problem.. And as said before, the scanner sends something every 5 secs or so and I haven't seen it going to sleep on any other vehicle..

  3. #13
    VENDOR - ScanTool Vitaliy's Avatar
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    Quote Originally Posted by Nitroking View Post
    So the command would be ATWM 010C?

    But regarding the problem, do you have any idea what is causing it? I think that before I set the headers there is no problem.. And as said before, the scanner sends something every 5 secs or so and I haven't seen it going to sleep on any other vehicle..
    C'mon man, you've got the ELM327 datasheet -- look it up. When you set up the wakeup message, you need to provide the headers along with the data.

    I don't know why the ECU times out. If you can connect a second scan tool in parallel, monitor the transmissions, and post the session here, we can try to decipher it together. If you can do it with timestamps (using a free serial port monitor or similar), so much the better.

    Best regards,

    Vitaliy
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  4. #14
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    Thanks Vitaliy, well my knowledge about electronics is not very good so sometimes I read things in the datasheet that I can't understand.. That's why I asked..

    I have a second scan tool and I can find a Y cable but I don't have a clue about how to monitor the transmission.. :P

  5. #15
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    OK I did some testing on the Tiguan 2.0T Auto transmission and this makes things even more complicated..

    The first weird thing I noticed is that the tranny ECU supports a lot of PIDs such as rpm, vss, absolute throttle position(?), even engine coolant temp.. And I'm asking, why ON EARTH would a tranny ECU respond on engine coolant? Since when do trannies have coolant? Or is this information that they share with the engine ecu?

    Second and most annoying is that the Engine ECU id is 7E8 and the tranny ECU id is 7E9.. The format of the messages is like 7E8 06 41 00 <data> blah blah.. The Bimmer is 86 F1 12 41 00 <data> blah blah.. So this makes the searching for the engine ECU even worse as in the bimmer case you just need to find the 86 and the 12 but in the VW case you need a 3 letter byte (7E8) which makes filtering a bit more complicated..

    The worst thing is that the AT SH command doesn't accept 3 letter bytes so I was not able to make queries only to the engine ECU.. Something interesting to note is that in case a PID is supported by the Engine ECU and not the tranny ECU, the tranny ECU shuts up and only the engine ECU is responding, for example, for 0110 (MAF) responds only the engine ECU, same for 0114 (narrowband oxygen sensor)..

    The 3 letter byte is probably because the VW is a CAN one as it is a 2009 model.. But how should I use the ATSH command in order to get responses only by the engine ECU?

  6. #16
    VENDOR - ScanTool Vitaliy's Avatar
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    Quote Originally Posted by Nitroking View Post
    OK I did some testing on the Tiguan 2.0T Auto transmission and this makes things even more complicated..

    The first weird thing I noticed is that the tranny ECU supports a lot of PIDs such as rpm, vss, absolute throttle position(?), even engine coolant temp.. And I'm asking, why ON EARTH would a tranny ECU respond on engine coolant? Since when do trannies have coolant? Or is this information that they share with the engine ecu?

    Second and most annoying is that the Engine ECU id is 7E8 and the tranny ECU id is 7E9.. The format of the messages is like 7E8 06 41 00 <data> blah blah.. The Bimmer is 86 F1 12 41 00 <data> blah blah.. So this makes the searching for the engine ECU even worse as in the bimmer case you just need to find the 86 and the 12 but in the VW case you need a 3 letter byte (7E8) which makes filtering a bit more complicated..

    The worst thing is that the AT SH command doesn't accept 3 letter bytes so I was not able to make queries only to the engine ECU.. Something interesting to note is that in case a PID is supported by the Engine ECU and not the tranny ECU, the tranny ECU shuts up and only the engine ECU is responding, for example, for 0110 (MAF) responds only the engine ECU, same for 0114 (narrowband oxygen sensor)..

    The 3 letter byte is probably because the VW is a CAN one as it is a 2009 model.. But how should I use the ATSH command in order to get responses only by the engine ECU?
    I don't see anything strange, except for the TCM supporting the coolant PID. In fact, the CAN standard says that the recommended CAN IDs are 7E8 for the ECM, and 7E9 for the TCM. So it's easy to tell them apart.

    Also, I am yet to see a TCM that supports more Mode 1 PIDs than an ECM.

    When you communicate on 11-bit CAN, you have complementary request/response IDs that you use for physical addressing:

    ISO 15765-4, Table 3 11 bit legislated-OBD CAN identifiers
    CAN identifier (hex) Description
    7DF CAN identifier for functionally addressed request messages sent by external test equipment
    7E0 Physical request CAN identifier from external test equipment to ECU #1
    7E8 Physical response CAN identifier from ECU #1 to external test equipment
    7E1 Physical request CAN identifier from external test equipment to ECU #2
    7E9 Physical response CAN identifier from ECU #2 to external test equipment
    7E2 Physical request CAN identifier from external test equipment to ECU #3
    7EA Physical response CAN identifier from ECU #3 to external test equipment
    7E3 Physical request CAN identifier from external test equipment to ECU #4
    7EB Physical response CAN identifier ECU #4 to the external test equipment
    7E4 Physical request CAN identifier from external test equipment to ECU #5
    7EC Physical response CAN identifier from ECU #5 to external test equipment
    7E5 Physical request CAN identifier from external test equipment to ECU #6
    7ED Physical response CAN identifier from ECU #6 to external test equipment
    7E6 Physical request CAN identifier from external test equipment to ECU #7
    7EE Physical response CAN identifier from ECU #7 to external test equipment
    7E7 Physical request CAN identifier from external test equipment to ECU #8
    7EF Physical response CAN identifier from ECU #8 to external test equipment

    While not required for current implementations, it is strongly recommended (and may be required by applicable legislation) that for future implementations the following 11-bit CAN identifier assignments be used:
    -- 7E0/7E8 for ECM (engine control module);
    -- 7E1/7E9 for TCM (transmission control module).

    To set up the IDs, you would use the same command (ATSH xyz).

    To monitor with a second scan tool, just type "ATMA" and you will see all the messages transmitted by the vehicle and the scan tool. You can use the mask/filter commands to block out messages that you don't want to see.

    Vitaliy
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
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  7. #17
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    Thanks, great info! Just a correction, the TCM is not supporting more PIDs than the ECM, it's just that the TCM supports some "weird" PIDs such as coolant temp and absolute throttle position.. But in total, ECM supports more than the TCM..

    Regarding the ATSH xyz command, I tried ATSH 7E8 (for ECM) and then I got NO DATA for each PID tested.. What did I do wrong?

  8. #18
    VENDOR - ScanTool Vitaliy's Avatar
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    7E8 is "Physical response from ECU#1". You need to send to 7E0.
    OBDLink MX: world's smallest, fastest, most advanced OBD/Bluetooth adapter with SW and MS CAN support. Read the review to learn more.
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  9. #19
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    OK now I got it.. 7E0 is always assigned to ECM or in some cases it can be assigned to TCM?

  10. #20
    Low Bitrate remus08's Avatar
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    Nitroking, the ELM327 allow to connect to several protocol, to make a good software, you will have to read SAE or ISO document which describes each protocol

    On this webpage, you can have a quick overview of standard, I know it's in french but you've got the listing

    http://www.outilsobdfacile.fr/presen...-communication

    Hope that will help

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