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Which lambda sensor is which please?

Discussion in 'A3/S3 Forum (8L Chassis)' started by martin g, Mar 15, 2010.

  1. martin g
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    martin g [censored]

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    Dealer put the car on the diagnostic today as the EM light came on after they did the camblet/waterpump. Showed two isssues, the stat and a lambda sensor. Now I intend to do both myself, I believe they are simple jobs, I have the stat and a new sender but I dont know which o2 sensor I need.

    Quote sheet states ' upstream' sensor, now I assume there is one either side of the cat, so would the upstream be the one nearest the engine?

    Care to give me a quick direction on where to find it please?

    I changed these before on other cars and assume its the same, they screw into pipe and of course link to the car via a simple snap connector.



    By the way, id like to say while i can a big thanks to all here, ive used a few forums over the years but this one is full of very helpfull modest people and your a credit to the forum and marque, maybe its an audi thing....seriously thanks.

    Martin
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  2. martin g
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    martin g [censored]

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    no? :idea:shamless bump
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  3. Sandip
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    Sandip Active Member

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    Hi Martin, there are 2 lambda's, pre cat and post cat. The pre cat would cause slight running issues if it was gone or going, post cat basically measure the work the cats doing.
    Now then where is the pre cat lambda > You have to look at the back of the engine, behind the charge pipe, you should be able to see a wire going to the downpipe, this is the pre cat lambda, follow the wire disconnect the plug. You will need a lambda socket this has a cut in it so it is possible to undo without cuttting the wire.

    Is the car running ok though? Decent mpg etc
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  4. badger5
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    B1S1 was it? bank 1 sensor 1 is upstream lambda and the main one which controls fueling..
    the one after the cat is checking cat efficiency

    What was the exact fault? sensor signal, heater or somethign else?
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  5. Sandip
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    Sandip Active Member

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    Bill mine brings up b1s2 is this post cat? And if so what's it saying exactly, does it mean my cat ain't working as well as it should? Thanks

    I've changed b1s1, pre cat by the way
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  6. martin g
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    martin g [censored]

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    The sheet they gave me is hand written, they kept the print out and that simply states 'lambda sensor upstream' and quotes price to supply and fit. As for running, Ive noticed at idle she starts at 1100 and drops to 900 or so when warmed up a bit and I think ive noticed a slight loss in power but this is slight and tough to say for sure, noticed more so when in 6th and I give it some pedal and the pick up just doesnt seem like it was. So Im quite sure it is the pre-cat sensor?

    This socket? can the job be done without it?
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  7. badger5
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    b1s2 is post cat yes.. and is either saying cat is'nt efficient or has a sensor fault itself.
    something like efficiency below threshold is a cat reported problem
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  8. Sandip
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    Sandip Active Member

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    Thanks for that Bill, do you think the car running lean top end has a link to this fault? Not sure if it's relevent but i did find a tiny hairline crack in the exhaust manifold not so long along, the car is running the same as it did at Ajec so the crack could be an old one thats been there for a while

    Martin > I think you might be able to change it without that socket but it'll be a real ass to do as there ain't much room lol I didn't want to butcher the old sensor so i bought a socket
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  9. martin g
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    martin g [censored]

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    Thanks all, but Im not sure where we got to?? did we agree the upstream sensor is the pre cat which is to the rear of the engine approached from the engine bay?? things kind of went off on a tangent :)
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  10. Sandip
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    Sandip Active Member

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    Yes Martin, pre cat, just behind the engine on the downpipe:)
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  11. badger5
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    possibly, but logs would confirm request fuel vs actual and lambda adjust going on
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  12. martin g
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    martin g [censored]

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    cheers ears, think i will do stat whilst I have the tools out too
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  13. martin g
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    martin g [censored]

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    Bit of an update

    The Engine Management light has now gone out?? was on yesterday, has been for a week or so, got in this morning, drove, stopped several times, on off, no fault.

    Are intermittent EML shows common?

    Also, could this be that my stat needs changing and any over fueling is annoying the o2 sensor and hence the fault showing, only difference today is the wet weather.

    Anyways, whilst the light is of, im not going to worry and wont change the o2 sensor unless it appears again, just going to change the thermostat this evening.
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  14. martin g
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    martin g [censored]

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    I gave up trying to change the stat....i only have a drive to work on and couldnt get to the lower fixing bolt at all, could see the little bugger but couldnt get at it. Im a time served mech fitter from a past life so know my way around the spanners but it still beat me, looks like it needs a long reach flexi drive or something. To make things worse, I snapped the dip stick tube off just by pushing it sideways out of the way GGGRRRRR. Temporary fix done but needs replacing.

    car is fine but was all a little frustrating, I will give in and spend the £100 and be done with it.
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