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Thread: Sample long coding and clarification for 2017 Jetta before purchase of HEX-V2

  1. #11
    Benevolent Dictator Uwe's Avatar
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    Yes, the DRL behavior is definitely controlled by the BCM.

    However, I do not think you can achieve what you desire with coding. I believe what you are looking to do would require modification of the EEPROM data in the BCM, which VCDS cannot do. Hence if this is the main thing you want VCDS for, I recommend against purchasing it.

    No, I do not think erWin would be helpful in any way.

    -Uwe-
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    Quote Originally Posted by Uwe View Post
    Yes, the DRL behavior is definitely controlled by the BCM.

    However, I do not think you can achieve what you desire with coding. I believe what you are looking to do would require modification of the EEPROM data in the BCM, which VCDS cannot do. Hence if this is the main thing you want VCDS for, I recommend against purchasing it.

    No, I do not think erWin would be helpful in any way.

    -Uwe-
    Thanks for your honest help! It is disheartening about the DRLs however looking at the wealth of resources and features offered by VCDS and the amazing help given by the community, I think I'm gonna go ahead and and order the HEX-V2 by today, thanks for all your help and looking forward to becoming a member of the VCDS community

    Kind Regards,
    gokarty

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    Verified VCDS User DV52's Avatar
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    Quote Originally Posted by gokarty View Post

    Meanwhile I have an interesting observation to point out. Last night I tried removing every single pin in the headlight switch individually but not a single PIN controlled the DRLs. However, when I start my car without the headlight switch installed, the headlights(low-beam) turn on, even though there is no switch!
    gokarty: hmm........ you certainly are somewhat of a "forum butterfly" (no offense intended) -I didn't know in which thread to post my reply to your repeated observation !!

    So - I wanted to suggest a reason why (perhaps) your observation above occurred and to do so, I've borrowed (in the picture below) a section of the WD from a mk6 Golf (because it appears to be closest in build platform for your Jetta). However, I emphasis from the outset that my picture is NOT from the 2017 Jetta WD - I don't have that particular WD.



    In the picture, I've shown the connections between the BCM and the rotary light switch and in particular how VW indicate the internal wiring for the LDS.

    Not sure how familiar you are with VW WD s, but they tend to use DIN 72552 standards which define "Terminal numbers" for the various electrical functions in a vehicle. As an example of how to read the WD (and I apologize in advance if you already know this stuff) take the designation for the pin on the extreme LHS of my picture on the LDS (called "E1") which is T10h /4 15a.

    For this pin on the LDS: T10 means that this pin is on a 10 x pin connector - 4 means that this is pin#4 - 15 means that this pin has "Terminal 15" function as defined in DIN 72552. Note that I have included on my picture the DIN 72552 functions for ease of reading.

    So- for the purpose of the observation in your quote, notice how the ganged, multi-pole switch-bar in E1 applies a T30 voltage to (nearly all) the BCM pins. Importantly for your observation, notice how the multi-pole switch does the opposite for the TFL pin (the DRL function): this pin on E1 has +12V applied in the normal state (which I read to be the normal DRL-ON state with the dial set in the 0 position).

    If you are following my explanation, I hope that you will see that when you removed the 10 x pins at the rear of the LDS - you disconnected the T30 voltage to the TFL pin on E1 and in effect this generated a DRL OFF signal to the BCM.

    Now, normally - because of the ganged nature of the multi-pole switch in E1, the DRL OFF signal would be interpreted differently by the BCM depending on which of the other pins on the BCM received a T30 voltage (i.e. which light function was selected by the driver). In this case however - none of the other pins on the BCM received a T30 voltage (because the other pins were un-plugged)- so the BCM simply interpreted the DRL OFF command as meaning turn-on the night-time lamps.


    QED

    Don

    PS:I can hear you saying to yourself "Bingo -if the Jetta has the same set-up, that's the answer to my SPST switch problem: I simply need to disconnect pin #9 on the LDS". However, as you have observed, this switches-on the low-beams and Parking lights. And, as I suspect happened when you disconnected the 10 x pins, the BCM also said "WTF is happening here? Where is the missing T30 voltage on my other pins telling me which night time lights to turn-on?" - which was translated more politely as a DTC on the CAN network as a "implausible state error"!

    So, I suspect that Uwe's conclusion above is correct (it normally always is correct), but with the exception that the WD is useful for the sole purpose of demonstrating why a SPST switch won't work
    Last edited by DV52; 03-30-2020 at 07:26 PM.
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

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  6. #14
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    Quote Originally Posted by DV52 View Post
    gokarty: hmm........ you certainly are somewhat of a "forum butterfly" (no offense intended) -I didn't know in which thread to post my reply to your repeated observation !!

    So - I wanted to suggest a reason why (perhaps) your observation above occurred and to do so, I've borrowed (in the picture below) a section of the WD from a mk6 Golf (because it appears to be closest in build platform for your Jetta). However, I emphasis from the outset that my picture is NOT from the 2017 Jetta WD - I don't have that particular WD.



    In the picture, I've shown the connections between the BCM and the rotary light switch and in particular how VW indicate the internal wiring for the LDS.

    Not sure how familiar you are with VW WD s, but they tend to use DIN 72552 standards which define "Terminal numbers" for the various electrical functions in a vehicle. As an example of how to read the WD (and I apologize in advance if you already know this stuff) take the designation for the pin on the extreme LHS of my picture on the LDS (called "E1") which is T10h /4 15a.

    For this pin on the LDS: T10 means that this pin is on a 10 x pin connector - 4 means that this is pin#4 - 15 means that this pin has "Terminal 15" function as defined in DIN 72552. Note that I have included on my picture the DIN 72552 functions for ease of reading.

    So- for the purpose of the observation in your quote, notice how the ganged, multi-pole switch-bar in E1 applies a T30 voltage to (nearly all) the BCM pins. Importantly for your observation, notice how the multi-pole switch does the opposite for the TFL pin (the DRL function): this pin on E1 has +12V applied in the normal state (which I read to be the normal DRL-ON state with the dial set in the 0 position).

    If you are following my explanation, I hope that you will see that when you removed the 10 x pins at the rear of the LDS - you disconnected the T30 voltage to the TFL pin on E1 and in effect this generated a DRL OFF signal to the BCM.

    Now, normally - because of the ganged nature of the multi-pole switch in E1, the DRL OFF signal would be interpreted differently by the BCM depending on which of the other pins on the BCM received a T30 voltage (i.e. which light function was selected by the driver). In this case however - none of the other pins on the BCM received a T30 voltage (because the other pins were un-plugged)- so the BCM simply interpreted the DRL OFF command as meaning turn-on the night-time lamps.


    QED

    Don

    PS:I can hear you saying to yourself "Bingo -if the Jetta has the same set-up, that's the answer to my SPST switch problem: I simply need to disconnect pin #9 on the LDS". However, as you have observed, this switches-on the low-beams and Parking lights. And, as I suspect happened when you disconnected the 10 x pins, the BCM also said "WTF is happening here? Where is the missing T30 voltage on my other pins telling me which night time lights to turn-on?" - which was translated more politely as a DTC on the CAN network as a "implausible state error"!

    So, I suspect that Uwe's conclusion above is correct (it normally always is correct), but with the exception that the WD is useful for the sole purpose of demonstrating why a SPST switch won't work
    Hi Don,

    thanks for your input!

    Yes that makes sense! After going through the wiring diagrams and the fuse assignments myself, I figured that there is no easy way of wiring an SPST / DPDT

    So, I guess I'm going to have to take the longer route of wiring a switch at the BCM output, however can you help me with a few questions that might sound dumb:

    1) According to the Wiring Diagram, I need to tap/disconnect a wire connected to pin 3 on a T73b connector, watching the Ross Tech videos (really helpful btw!) I know that it's a 73-pin connector connected to the BCM, but since it also has a "b" that means that there already are other 73-pin connectors used in the diagram, how do I locate the correct connector and pin 3 on the BCM?

    2) After locating the connector, how do you open it? Is it possible? I figured rather than cutting wires, it's safer (and easier to reverse) to remove the wire from the connector and make my own circuit with a SPST that plugs in

    Also, here is the wiring diagram for your reference : https://imgur.com/a/SHcHcBb

    Mu understanding is I need to wire a switch inline with the blue/white wire that runs to "L174" Left Daytime Running Bulb

  7. #15
    Verified VCDS User DV52's Avatar
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    Quote Originally Posted by gokarty View Post
    Hi Don,

    thanks for your input!

    Yes that makes sense! After going through the wiring diagrams and the fuse assignments myself, I figured that there is no easy way of wiring an SPST / DPDT

    So, I guess I'm going to have to take the longer route of wiring a switch at the BCM output, however can you help me with a few questions that might sound dumb:

    1) According to the Wiring Diagram, I need to tap/disconnect a wire connected to pin 3 on a T73b connector, watching the Ross Tech videos (really helpful btw!) I know that it's a 73-pin connector connected to the BCM, but since it also has a "b" that means that there already are other 73-pin connectors used in the diagram, how do I locate the correct connector and pin 3 on the BCM?

    2) After locating the connector, how do you open it? Is it possible? I figured rather than cutting wires, it's safer (and easier to reverse) to remove the wire from the connector and make my own circuit with a SPST that plugs in

    Also, here is the wiring diagram for your reference : https://imgur.com/a/SHcHcBb

    Mu understanding is I need to wire a switch inline with the blue/white wire that runs to "L174" Left Daytime Running Bulb
    GoKarty: hm......... I'm not entirely sure that you wiring diagram is correct for your specific car - but first, let me answer your questions:

    Question 1): You are indeed correct in assuming that "there already are other 73-pin connectors". In fact, the "other 73-pin connector" is actually on the same PQ25 BCM. When a BCM pin on a WD has the alpha "a", "b" (or "c") - it is referring to the connector that has the same alpha stamped in capital letters on the BCM housing. So T73b /3 means pin #3 on the 73 x pin connector on socket B. Here's how to find socket B on a PQ25 BCM:



    If you look again at your WD, you will see mention of T73a - this is socket A in the picture above

    Question 2) Each of the sockets on the BCM normally have their -own retaining catches to ensure that the connections don't shake loose. It's normally just a matter of releasing the catch, then forcing one end of the socket slightly inwards - but I suggest that you get hold of the Electrical systems document for your Jetta which will describe the location of the BCM and how to release the catch - if you want.

    However - a few other matters that you might want to consider before proceeding:
    1. As I prefaced in my opening remarks, your wiring diagram seems a tad strange because you have mentioned in a previous post that the DRLs on your car are a LED string. Worryingly however, the WD shows a headlight assembly that consists entirely of incandescent lamps. I've no doubt that the WD is for a Jetta - but I suspect that the specific wiring arrangement in your picture isn't the correct headlight option for your car. Whilst it's highly likely that the same BCM pin is used for the DRL on your fitting - I always prefer to eyeball the correct WD as positive confirmation before cutting any wires on a car
    2. You might want to think further about cutting the BCM output pin to the DRLs and using a separate switch to turn ON/OFF the lamps: the PQ25 is a sophisticated device which contains it's own fault monitoring circuits. If the BCM senses that there is no electrical current flow when it energizes the DRL output pin (because your new switch has open-circuited the wire to the LED strips) - it will generate a DTC with an accompanying message on the dash indicating a faulty fitting.
    3. If you proceed, you might think about NOT doing any splicing/cutting at the BCM socket: it's cram packed with other wires and generally it's not a good place to make modifications unless absolutely necessary (IMHO) : it's far easier I suspect to make connections in the engine bay loom where access is more straight-forward (if you want to proceed)


    Don
    Last edited by DV52; 04-01-2020 at 12:46 AM.
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

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  9. #16
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    Quote Originally Posted by DV52 View Post
    GoKarty: hm......... I'm not entirely sure that you wiring diagram is correct for your specific car - but first, let me answer your questions:

    [...]
    Don,

    Thank you for the clarifications and help, I'm going to try and find a wiring diagram with the LED strip accounted for, if that's not possible, I'm gonna try using a DMM at the headlight connector to figure out which wire controls the DRLs

    Thanks for your help!
    Last edited by Uwe; 04-01-2020 at 03:10 PM. Reason: Snipped Quote

  10. #17
    Verified VCDS User DV52's Avatar
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    gokarty: Please understand that while I'm more than happy (ecstatic - in fact) to answer your questions, I'm certainly NOT recommending that you proceed in your endeavor (for the reasons I've stated).

    Ultimately however, I assume that you are a sane, sentient being - with the mental capacity to make your own decisions!!

    Good luck and please keep us (me, really) informed of progress !!

    Don
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

  11. #18
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    Quote Originally Posted by DV52 View Post
    gokarty: Please understand that while I'm more than happy (ecstatic - in fact) to answer your questions, I'm certainly NOT recommending that you proceed in your endeavor (for the reasons I've stated).

    Ultimately however, I assume that you are a sane, sentient being - with the mental capacity to make your own decisions!!

    Good luck and please keep us (me, really) informed of progress !!

    Don
    Don, thanks for your input, will keep you posted
    As for now, I'm not doing anything until I have done some more research and can be more confident in my abilities!

    Thanks and Regards,
    gokarty

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