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Function tests

Discussion in 'VCDS (formerly VAG-COM) forum' started by Pornstarr, Apr 15, 2008.

  1. Pornstarr
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    Pornstarr Member

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    [Apr 15, 2008]
    I know Vagcom allows you to run the output tests.

    But will it also run function tests like the Audi 5051 systems do?
    For example, the 5051 can run a test on the fly by wire throttle pedals to show the full range of output including the voltage signal, and tell you if it is working correctly.

    ???
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  3. Uwe@Ross-Tech
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    Uwe@Ross-Tech Member

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    [Apr 16, 2008]
    As a general rule, you can reproduce such a function test with VC if you know what the VAS is actually doing during such a test. The whole "Guided Functions" thing is nothing but a bunch of scripts that use the same functions you'd find in Self-Diagnosis or VC. Unfortunately, figuring out what it's actually doing during such a test can be a bit arcane. But if there's a particular test you're interested in, give us the details and we'll see if we can't get you suitable procedure. Note: Such procedures are often specific to a particular engine code.

    -Uwe-
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  4. Pornstarr
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    Pornstarr Member

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    [Apr 16, 2008]
    Thankyou for your reply Uwe.
    I'm pretty sure there's a problem in communication between my throttle pedal and throttle body.
    So I'm trying to figure out which one it is. Doing what I can on VC, neither of them is showing a fault. However, at full throttle, my logs are only peaking at about 56% throttle opening.

    Presuming it's not a mechanical failure....I can only presume there's a communications problem. So starting at the pedal, I'd like muchly to know if it's transmitting within range, the correct signal.

    Mine's a B5 S4 avant, pre-face lift. Making, I believe, the engine code AGB.

    Feel free to correct me if I have any misgivings along thought process.
    Whilst mechanical maintainance is de rigour for me, this new self diagnostics lark is new.

    Many thanks.
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  5. Uwe@Ross-Tech
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    Uwe@Ross-Tech Member

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    [Apr 17, 2008]
    You realize that the throttle pedal does not communicate with the throttle body, right?

    The ECU reads the position of the throttle pedal. It interprets this as a request for torque. Then the ECU commands the throttle to open however much it thinks is needed to produce the amount of torque it thinks the driver is calling for (talking into account RPM, available boost, and a number of other factors).

    Take a look at what you have in Measuring Block Group 062, this may shed some light on things:
    http://www.ross-tech.com/vag-com/m_blocks/060-069.html

    Bear in mind that each of the sensors pairs on both the throttle and the pedal go in opposite directions (allowing the ECU to do a plausibility check a detect a failed sensor) and that none of them will likely reach 0% or 100% (again, to allow the ECU to detect a failed sensor).

    -Uwe-
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