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Lambda Sensors

Discussion in 'A3/S3 Forum (8L Chassis)' started by AL_B, Aug 13, 2005.

  1. AL_B

    AL_B Active Member

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    Hi guys,

    Need your help again. The saga of the hesitation problem of my S3 continues. (see numerous other posts)

    Last week I eventually got round to performing the downstream and upstream lambda sensor checks as suggested by Evotista and HTC.

    These can be downloaded from HTC's site.

    http://homepage.ntlworld.com/kevin.yeoman/CheckingLambdaControlDownstreamOfCat.pdf
    http://homepage.ntlworld.com/kevin.yeoman/CheckingLambdaControlUpstreamOfCat.pdf

    (hope you don't mind me posting the links HTC)

    I was advised by Martin (Evotista) to check the downstream lambda sensor first. Which I did using VAG-COM.

    In the downstream doc above, looking at block 30, its says Bank1-Probe2 (which is the downstream one) should reach a value of 110 at least once. Well, in the 10-15 minutes doing the test on idle, it didn't reach that value.

    I decided to move onto the upstream sensor anyway, about another 10 mins later. Following the test steps, you look at block 30 again, this time Bank1-Probe2 achieved the 110 value. A full 20 minutes late!!

    Any idea why? Do you think the sensor may be playing up? There are no error codes.

    After work this evening I ran a VAG-COM check and looked at block 30 again. This time the Bank1-Probe1 value was 010. The first digit should fluctuate between 1 and 0, repeatedly. It wasn't doing.

    Anyone else seen this?

    All help appreciated as usual.

    Cheers

    AL

    PS: As you can see from the time of this post, I am starting to loose sleep over this fr#ckin problem!
     
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  3. evotista

    evotista Member

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    Al,

    Sorry not replying to your pm earlier than this...as you can see some of us are up ridiculously early as well as late on a weekend (kids eh)

    I'm no expert on this...HTC and others are more experienced certainly....all i can say is that when i ran the procedures on my 1.8TQ the values checked out immediately on BOTH probes, no need for 20 minutes to elapse. I would have thought this is good enough on its own to take back to links, get them to VAG block 30 hopefully confirm the same as you, and replacement lambdas are yours. I wouldn't be too concerned about lack of fault codes.....it should certainly be flipping the 1 to 0 and back again constantly. Given everything else you've tried and replaced i think that this has to be the next most likely suspect.

    I'm sure HTC or Ess can comment better than me technically. Keep us all informed.

    Martin
     
  4. Drill

    Drill Member

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    Someone remind me which is upstream, and which is down cause I'm cleaning mine today or tomorrow /ubbthreads/images/graemlins/confused.gif


    Al, let us know how you get on with these.... I'm starting to suspect that these are the "New" Coilpacks /ubbthreads/images/graemlins/crazy.gif

    /ubbthreads/images/graemlins/beerchug.gif
     
  5. PaulRS3

    PaulRS3 Well-Known Member

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    probe 1 (upstream) before cat

    probe 2 (downstream) after cat.


    bank 1 (there is only one bank)

    would be bank1 and bank 2 for v6's v8's etc.
     
  6. Drill

    Drill Member

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    Thx /ubbthreads/images/graemlins/beerchug.gif
     
  7. Khufu

    Khufu Well-Known Member

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    As said, unless the readings are out of range, an error wont be reported for then lambda sensor when it still could be faulty. Alan, have you tried to just clean it (them?) yet?
     
  8. Drill

    Drill Member

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    Good point Ewan /ubbthreads/images/graemlins/crazy.gif

    I just spoke with my mechanic on Friday and he recommended straight brake cleaner to clean the Lambda sensors /ubbthreads/images/graemlins/angel.gif Plan is to give it a go this Friday (If I can get the Upstream Sensor off /ubbthreads/images/graemlins/frown.gif)

    /ubbthreads/images/graemlins/beerchug.gif
     
  9. Khufu

    Khufu Well-Known Member

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    let us know how you get on M /ubbthreads/images/graemlins/beerchug.gif
     
  10. AL_B

    AL_B Active Member

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    Evotista, no problem mate.

    Drill, Ewan,

    I'd not heard about cleaning them. I could give it that a go first. Is the downstream one easy to get at?

    I have axle stands, trolley jack, but never used them on this car. Any tips for placement? Pic's would be ideal please. PM me and I'll give you my email address.

    Cheers

    AL
     
  11. Little_Si

    Little_Si Member

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    Al,

    As far as I am aware, the downstream probe should have no effect on engine performance. It is simply used to measure post-cat oxygen levels to make sure the cat is operating correctly. No harm in cleaning it, but I don't think you'll gain anything.

    Anyone correct me if I'm wrong though.
     
  12. AL_B

    AL_B Active Member

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    Thanks Si.

    Can anyone confirm or deny what Si is saying?

    Cheers

    AL
     
  13. JamS3

    JamS3 Active Member

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    Does anyone know the answer to the above question?? Ess??
     
  14. Mo-S3

    Mo-S3 Member

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    Hi Al, hope your well
    have you had them both replaced yet ??
     
  15. Ess_Three

    Ess_Three Active Member

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    [ QUOTE ]
    Does anyone know the answer to the above question?? Ess??

    [/ QUOTE ]

    I was under the impression that the d/s lambda sensor measures the cat's efficiency as suggested, and will throw an engine check light if the cat efficiency is deemed to be too low.

    This suggests that it's more than just a reading...why fit it, if it's not tied into the management?

    As to whether a defective cat, or defective lambda probe could actually cause the engine to hit limp mode has never been proven...I can't see why not...if the ECU thinks the engines efficiency has gone way out of spec, it's possible to limit performance (limp mode) to protect the engine or environment.

    I've seen many 'catalyst efficiency below threshhold' DTCs logged...usually due to Milltek's barely efficient cats...but I've never proved that performance was limited - the engine check light would come on...but I can't honestly say I proved one way, or the other, that the ECU was limiting power.

    Either way, in this instance, I personally can't see the lambda sensors causing a hesitation problem without flagging an engine check light up. But who knows...?
     
  16. Drill

    Drill Member

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    Hey Glen, does the ECU use Lambda input to detect lean / rich conditions? If so, wouldn't it also use that signal to advance / retard timing accordingly??

    Just remember hearing something along those lines /ubbthreads/images/graemlins/confused.gif

    /ubbthreads/images/graemlins/beerchug.gif
     
  17. Khufu

    Khufu Well-Known Member

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    i thought the lambda sensors measured the oxygen content and adjusted the mixture and the knock sensors are used to advance and retard the timing out with the normal vaccum advance and retard. Just out of interest, does the latter S3 have 4 lambda sensors /ubbthreads/images/graemlins/blush.gif
     
  18. HTC

    HTC Active Member

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    APY engine code has one lambda sensor.

    AMK and BAM codes have two.
     
  19. recomdos

    recomdos Member

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    My car this reporting an error code on the lambda sensor at the moment. I've been told they cost approx £100 to buy the sensor. Anyone got a rough idea how much they cost to fit/replace (roughly).

    Or any more advice?

    Thanks chaps! /ubbthreads/images/graemlins/laugh.gif

    Rob
     

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