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Emission Control System Light :-(

Discussion in 'A3/S3 Forum (8L Chassis)' started by A3 T, Feb 25, 2013.

  1. A3 T
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    A3 T Lord Of The Rings

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    Driving along today and this light pops up:

    [​IMG]



    I gave the car a vagcom scan when i got home and it come up with this:

    16804 - Catalyst System: Bank 1: Efficiency Below Threshold
    P0420 - 35-00 - -
    Readiness: 0000 0000


    Could this all be related to my other threads:


    http://www.audi-sport.net/vb/a3-s3-forum-8l-chassis/180508-car-almost-dies.html


    The difference now is that the 17705 code didn't show up (maybe because I've not been booting the car around) this 16804 code is no longer saying “intermittent” but now says “Readiness: 0000 0000”.


    I'm guessing its time to change the pre cat lambda sensor


    Any ideas ?
    Last edited: Feb 25, 2013
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  2. Alex C
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    Alex C Well-Known Member

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    could it be fuel pressure regulator sticking? over fueling at low rpm - stalling - having to give it more rpm to keep it going? perhaps boost leak also? Would a sticking FPR throw a more definite fault code? I'm guessing really - but i would take a look at the FPR

    EDIT - you'd get lambda errors - ignore
    Last edited: Feb 26, 2013
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  3. A3 T
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    A3 T Lord Of The Rings

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    A guessing reply is better than no reply ;)


    I think my 16804 code is the lambda mate.
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  4. Alex C
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    Alex C Well-Known Member

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    yeah but its the post CAT lambda identifying that your CAT isn't doing its job properly i think - which i why i was thinking that maybe un-burnt fuel had damaged the CAT due to an over-fueling issue possibly caused by an FPR issue. But if that were the case you'd probably get a fuel system too rich error as well which you don't have.

    Could always have a look at the FPR - no harm done
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  5. A3 T
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    A3 T Lord Of The Rings

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    oh ok mate.

    Thanks for the replies, you seem to be the main (sometimes only) poster in my threads.....lol
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  6. Vwdan80
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    Vwdan80 Member

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    Since you have vcds you can do a lambda sensor ageing test and a cat ageing test to see what the condition is before changing anything :)
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  7. A3 T
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    A3 T Lord Of The Rings

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    I didn't know you could test them with vagcom.


    Do you know of any guides?
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  8. Vwdan80
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    Vwdan80 Member

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    I did find a guide on how to do it on vwvortex forum, if you google 'lambda sensor ageing test vw' it'll come up. It's some good info to read up :)
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  9. Vwdan80
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    Vwdan80 Member

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  10. A3 T
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    A3 T Lord Of The Rings

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  11. Vwdan80
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    Vwdan80 Member

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    You need to warm the engine up, doing the tests with the car running, I think that the cat needs to be over 400c for the tests to initiate, just follow the guide for the initiation procedure :)
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  12. A3 T
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    A3 T Lord Of The Rings

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    So i warm the car up and...



    Block 034 - Aging of Pre-Cat Oxygen Sensor

    - Go to Block 034 (this test must be done in basic settings, not measuring blocks). Depress and hold brake pedal to run the automated test. The engine RPMs should raise to around 1400. Field 1 is the engine speed. Field 2 is the catalytic converter temp. Field 3 is the value which tells you how aged the sensor is (not sure what it's called). Field 4 will say either 'TEST OFF/ON' before/while the test is running and either 'B1-S1 OK' or 'B1-S1 NOT OK' after the test is finished. The aging value must be above 0.80. The value for a new sensor is 1.99. The value will decrease as the sensor ages. Release the brake pedal after the test finishes.



    And after the test it will say 'B1-S1 OK' if the sensors good or 'B1-S1 NOT OK' if the sensors f***ed.



    Does that sound about right ?



    Also with the AUM engine do i depress and hold the brake or keep the revs between 1800 and 2200 as said here:



    http://forums.vwvortex.com/showthread.php?1672645


    I didn't have time to try anything today but i did read about checking the readiness option in vagcom and this is what come up (with the engine cold and off):


    [​IMG]




    Does this mean anything....lol
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  13. A3 T
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    A3 T Lord Of The Rings

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    Anyone ?

    Or is this another one that's a bit over your heads.....lol
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  14. Vwdan80
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    Vwdan80 Member

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    I would try both the procedures you have said of and I'm sure one of them will work, you can't do any damage, I'll try it on my car tomorrow just to make sure :)
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  15. A3 T
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    A3 T Lord Of The Rings

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    Ok mate ....lol
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  16. Vwdan80
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    Vwdan80 Member

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    i have just tried the ageing tests and they work fine on my s3.
    To activate them the cat needs to be over 350'c and you have to hold the revs manually to over 2200 rpm and hold them there throughout the tests. you have to do complete sensor one test first then sensor 2 test then catalytic converter test after that.
    just for reference my first sensor had a dynamic value of 1.1 and on the cat test the value didnt go above 0.01 during testing.
    Hope this helps you confirm if the cats nackered :)
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  17. A3 T
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    A3 T Lord Of The Rings

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    Thanks mate.

    I've just logged in to give an update and you've beaten me to it.....lol


    I did the tests today but it was different to how you described it.

    For me as soon as i went to block 034 the accelerator pedal stopped working.

    I had to go hold down the brake pedal and then push the accelerator all the way down , as soon as i did that the revs slowly increased to about 2000 and the test started.

    When it had finished i got the message “B1-S1 OK”, So i went on to do the block “046” test and that straight away said “Cat B1 OK”

    So i followed up with a block “036” and that straight away said “B1-S1 OK”.

    What I'm finding a bit strange is why block 046 and 036 show that message before i even do the test. And now even if i go to block 034 it says “B1-S1 OK” before i even do a test.


    Something else i noticed today is that my revs with no air con on ...etc sit at around 720 and I'm sure the VAC is sitting at around 23psi at idle.
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  18. Vwdan80
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    Vwdan80 Member

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    It's the ageing value of the cat and sensors that you need to look at as they tell you how old they are and if they are nearing the end of their life, rather than just the ok or not ok bit.

    the tickover bit sounds ok my car idles the same. But the vac doesnt sound right
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