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catalyst engine light

DanVag May 13, 2018

  1. DanVag

    DanVag New Member


    The guy I brought my S4 off removed the back CAT's and didn't install the rear lambda sensors. I have been told I can just drill a hole in the current exhaust and install them? Is this correct?

    I am a bit dubious as the sensor will record different information without the CAT being installed.

    Just need some advice to clear this engine light and get these sensors installed and working correctly.

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  3. Jon13s

    Jon13s Member

    I could be wrong but doesn't the running of the car depend on the pre cat lambda sensors? The post cat ones only check that the cat is working.

    If he's removed the cats then chances are the light will come on if you fit the sensors.

    Sent from my SM-A520F using Tapatalk
  4. DanVag

    DanVag New Member

    If that was the case surely aftermarket exhaust systems without the back CAT wouldn’t be a thing?

    Sent from my iPhone using Tapatalk
  5. Retroman

    Retroman Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)

    As said above, the post-cat lambda sensor is there to monitor the efficiency of the cat. If it is just removed (and the wiring taped up for example) the ECU will receive an implausible signal and trigger a warning light on the instrument panel. Whilst I haven't done this sort of thing myself, I assume that the ECU needs some sort of "map" to "delete" the post cat sensor(s) to avoid a warning light - which may otherwise cause MOT issues if illuminated. Lambda sensors normally go into s strategic point (threaded) in the exhaust and so I have doubts that one can just drill a hole (in an aftermarket exhaust section) and poke one back in.

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