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Thread: Mk7 Golf Gti multiple errors. Throttle body, reference voltages, engine sensors.

  1. #21
    NostraJackAss Jack@European_Parts's Avatar
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    "Success - I've found the source of the 5V rail in the engine harness", I thought initially - but looking closer, how does the arrangement shown work? How can it work? How can a 12v fuse be connected to a 5V supply - even with the asterisk conditionality noted on the WD? I hate VW's WD s -What am I missing?

    Don
    To answer Don's question with a question hey what's this T105/35 from J623 do?...........

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  2. #22
    Verified VCDS User DV52's Avatar
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    ^^^ Jack - it must be my thick Aussie accent, or the fact that Antipodeans speak quickly (I apologise for both) - but what you have highlighted on your WD is EXACTLY what I have "boxed" on my WD - see post #12 on this thread.

    As I have said:

    Quote Originally Posted by DV52 View Post

    My first hypothesis was that the 5V rail in the engine prewiring harness was produced by the 2 x pins on the ECU that I have boxed in my WD above. But this doesn't make sense since your method allows for the DTC to remain (wrong- I meant "clear"] with the T105 connector pulled (this implies that the 5Volt rail is produced elsewhere).
    Don
    You are suggesting that T103 /35 is the power source for the 5V rail in the engine prewiring harness (and by inference, T105 /33 is the earth for said 5V rail). Good - we both agree!!

    BUT- consider the implications of our mutual agreement on your methodology: If the T105 connector is pulled - then as a consequence, the 5V supply disappears from every sensor, sender, valve etc that relies on the prewiring harness power supply.

    You have asserted (and I have accepted) that if "the the fault doesn't reset with ECU unplugged on engine harness side, th[e]n there is a problem at ECU"

    This method allows the counterfactual scenario: that is - "the fault" is reset - meaning that the "problem" is NOT in the ECU.

    So here's the issue - if the 5V rail is indeed generated in the ECU (as I think we both agree) and if the connector that distributes this power supply to the myriad of sensors, sensor etc in the prewiring harness is pulled - how can the DTCs ever be cleared?

    Without intending any offense - doesn't this dichotomy mean that if the T105 connector is pulled - the result of the methodology will ALWAYS point to a faulty ECU (i.e. resulting in false positives when the fault may be elsewhere)?

    This is do'in my head-in big-time . I'm desperately trying to understand where the logic in my thinking is wrong - help!!!

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

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  4. #23
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    I'll try to explain in couple simple words:
    The 12V to 5V converter is inside ECU. This convertor has an overload protection. Output voltage is monitored. If it is out of spec, ECU stores fault code.
    The biggest part of sensors, but not all, powered from this 5V converter is located in engine compartment and wired to ECU via T105 connector.
    Pulling it will induce a lot of new fault codes stored, but the one for 5V supply out of range should become stored as intermittent and be clearable, if overload/short circuit is in wiring or sensor behind T105.
    The same 5V supply inside ECU is connected to another pin at second connector. Mainly for APP sensor.
    If 5V supply fault code remains permanent with T105 pulled, problem is either in APP sensor/wiring to it, or internally in ECU.

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  6. #24
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  8. #25
    NostraJackAss Jack@European_Parts's Avatar
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    This is do'in my head-in big-time . I'm desperately trying to understand where the logic in my thinking is wrong - help!!!

    Don

    What Martin said Don ......"fuck yeah"!

    Unplugging Engine side harness and not gaining the 5 volt after DTC reset isn't always mean it's an ECU, but has indicated a bifurcation point to diagnosis path.

    Now if after only supply powers, ground and CAN are connected & the ECU wakes up for 5 volts on ECU engine harness side plug, than now you know it's not ECU and the plug on that side is suspect for any sensor or consumer.

    Hence why I recommend always bench harness to check status of ECU isolated.

    Last edited by Jack@European_Parts; 02-07-2020 at 05:32 PM.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
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  9. #26
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    Now if after only powers ground and CAN are connected & the ECU wakes up for 5 volts on ECU engine harness side plug than now you know its not ECU and the plug on that side is suspect for any sensor or consumer.
    This is more correct. More 5V consumers than only APP sensor may be connected to ECU via "body harness side" connector.

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  11. #27
    NostraJackAss Jack@European_Parts's Avatar
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    Martin is my hero tonight!


    Don you can be a hero too!
    European Parts Emporium/Performance / Immobilizer Solutions EPE
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    Above Magic! No Written record, AUTO-SCAN or Appointment = NO HELP!
    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email or call facility for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

  12. #28
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    Quote Originally Posted by DV52 View Post


    "Success - I've found the source of the 5V rail in the engine harness", I thought initially - but looking closer, how does the arrangement shown work? How can it work? How can a 12v fuse be connected to a 5V supply - even with the asterisk conditionality noted on the WD? I hate VW's WD s -What am I missing?

    Don
    You are missing taking into account that fuse assignment section is universal overview of what may or may not be connected to/powered from fuses shown there. Exact information is given at *, *1 and *2. Some specific in VAG WD's...
    Believe me, some other manufacturers have much more strange, stupid and even absolutely incorrect things in official factory WD's and repair manuals

  13. #29
    Verified VCDS User DV52's Avatar
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    ^^^ MartinsX: Many thanks for making time to comment on my quandary and for sharing your knowledge - yes, I entirely understand the "universality" of the WDs and the impact of the asterisk qualifiers.

    Of course, I agree that the only way that the diagram can make sense is to ignore the overt suggestion in the circuit that the 5V rail is connected to a 12V fuse. Notwithstanding that the WD reads (strongly suggests?) as if this is what happens, to interpret the circuit arrangement in this way ignores the basic laws of physics.

    My point - obviously not made clearly - is for VW to devote 99% of an entire page in their WD to a patently nonsensical ciruit description - and then to dismiss the entire diagram through the small-print asterisk notes, is........well difficult to understand IMHO!!

    Don

    PS: thanks also for your explanation of the T105 pin disconnection procedure - I wasn't aware that the 5V rail was internally wired to another pin on the T91 connector in the ECU
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

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