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Which o2 (Lambda) Sensor do I replace?!

Discussion in 'A3/S3 Forum (8L Chassis)' started by Leafsfan117, Aug 13, 2013.

  1. Leafsfan117
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    Leafsfan117 New Member

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    Hi guys, this is my first post and won't be my last due to having my work cut out for me with an Audi A3 8L I purchased with the intention of repairing.

    Apologies if there is already a thread for this, or if my question is really dumb!

    Okay so my revs have been hunting on starting the car, and when bringing the clutch to bite to pull away the revs drop all the way down and nearly stalls the car (I have to dip the clutch to keep the engine running).

    I'm guessed it's either the throttle body or o2 sensor, but before doing anything I ran a scan on VCDS which threw up the following code:
    00525 - Oxygen (Lambda) Sensor (G39): Signal too Low

    Therefore I'm guessing this is the best place to start. My question then, is how do I know which sensor needs to be replaced? The one before or after the cat?

    Also, does this sound like the possible solution to the problem I'm getting? Seems strange that the lambda would cause this issue.

    Thanks guys!!!
    Last edited: Aug 13, 2013
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  2. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    usually says bank 1 or or bank 2 also...

    bank one pre cat, bank 2 post cat

    not a 1.8t I presume?
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  3. Leafsfan117
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    Leafsfan117 New Member

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    No it's a 1.6 sorry I should have said!

    You were right I checked the scan and it states S2B2 is affected, I'm guessing that means bank 2? So that's the post cat right? I'll replace it and post to advise how I got on.
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  4. Leafsfan117
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    Leafsfan117 New Member

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    Hi guys,

    I took out the lambda and checked for any wire breaks and then checked with a mulitmeter, but the post cat lambda is fine?

    Any other reason it would show this fault and I would get these symptoms? Revs hunting and loss of power when pulling away/reversing?
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  5. mattyboy199
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    mattyboy199 Active Member

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    soak it in vinegar for a week, should clean it up nicely & then work fine
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  6. Leafsfan117
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    Leafsfan117 New Member

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    But again, will this resolve the problem I am getting with loss of power? Surely the post cat sensor only monitors the condition of the cat and makes no changes to the revs etc?

    I'm wondering perhaps if it's worth checking for wear or splits in the vacuum pipes?
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  7. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    is the cat blocked?
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  8. auditech12
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    auditech12 New Member

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    Just Replace it UNLESS you have an option to read "Live Data" of the O2 Sensors. Then you can check if the sensor is being "Lazy" in that case you would replace it.

    Check This Link: 00525 - Ross-Tech Wiki
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