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Thread: Techy Question: O2 Sensor?

  1. #1


    Hi All,

    Ok, I recently had a recurring problem with my Scoob. It's a MY99, bog standard, and has been experiencing an intermittent mis-fire, sometimes chronic, lapsing onto three cylinders, cutting out etc.

    A couple of visits to the dealership yielded no result. Then the check engine light came on for about 5 minutes while the car was experiencing one of it's 'foibles'.

    It went to the dealership that night who stated that this light prompted a download onto the ECU, which would make the identification of the problem much easier.

    After a day, picked it up and a great improvement is obvious, with no further mis-fire so far.

    The apparent cause was a faulty 'O2 sensor' (oxygen?).

    Does this sound credible to you guys? It's all a bit above my head so if anyone can put me out my misery, (so to speak), I would be very grateful.

    Thanx in advance


  2. #2


    Snap. Exactly the same symptoms. Exactly the same response form the dealer - "no errors logged, don't know what the problem is, doesn't happen when we test it!" almost as if they thought I was making it up! Got a check engine and took it straight back to dealer who said - "Lambda sensor error" (which is, I believe the same thing as 02 sensor) They changed it and things got a lot better.

    However I'm still not happy with the lack of smoothness under light to medium acceleration, which the dealer couldn't reprodiuce when the car went in again. It hessitates at about 2500 (I guess when the turbo starts spining up) and then again at 3000. It's just not as smooth as it used to be. Anyone got any ideas?

    MY99 UK Standard. 19000 Miles.

  3. #3



    no.1 - when the lamda sensor is faulty the ECU will show an error code in memory when connected to the Select Monitor - dealer should spot this straight away.

    however it is possible for the sensor to be partially working... when this happened to my car, the sensor did respond a bit but it was taking far too long to weaken the mixture again after the throttle was lifted - thus the cross-over points on the monitor were few...result was over rich running which in itself isn't too bad - certainly didn't run roughly or misfire - just tons of soot from the exhaust (clouds of it on heavy acceleration) and worse fuel consumption.
    If you suspect the O2 sensor it is possible for the dealer to get a live trace up on the select monitor for the lamda sensor and for its activity to be monitored whilst the car is revved/driven - should show any erratic behaviour very clearly.

    not convinced that this is your problem though, but maybe worth getting the dealer to run a live trace on the select monitor with you driving to re-create the problem ?


    Paul W

  4. #4



    Hoorah! Someone at last with the same problem!! My car is the same year as yours and has even done 19,000 miles!!!
    Your symptoms are exactly the same as mine, even down to the rev range problem. The car is, as you say, still not as smooth as it was but doesn't seem to suffer as regards performance.

    I believe the dealer will never actively reproduce the problem unless they have a rolling road, when the car can be long term tested with computer wizadry, while it is being 'driven' under load.

    Have you had yours on a rolling road?


    ps Cheers Paul, thats more info to take to the dealer.

  5. #5


    ...........add to above. On the way to work this morning the check engine light was on again and car repeatedly lapsing onto three cylinders. Never has a well made german marque looked so good......

  6. #6


    Sorry to hear it's happened again, but at least it may give your dealer something to go on.

    Mine's going to a different dealer when it gets to it's next service - probably end of June. I hope they are better at diagnosing faults that don't necessarily show up on the select monitor.

    I don't know of any dealers who have access to 4 wheel rolling roads. Are there any? Or does all testing get done on the road?


  7. #7


    Go the car back again on Saturday morning.

    This time the dealer has fitted a brand new sensor "and all associated wiring".

    Used it extensively over the weekend and so far, no problems.


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