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Check Engine Light after fitting 3" DP and 200 cel cat

Discussion in 'A3/S3 Forum (8L Chassis)' started by vrbob, Sep 7, 2012.

  1. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Hi Peeps,

    Just a quick one really, Since fitting my new relentless 3" downpipe and 200 cell cat the check engine light has come on twice now. Both times it has taken a good 50-60 miles before the light has come on. When i scan the car it says catalyst effeciency too low (cant remember exact code).

    Is there anyway to solve this or can someone explain why this is happening as i am using the OEM lambda sensors from the old system so (which were working fine). I have heard it can be coded out but i thought that was only if you were using a decat not a sports cat. Can i code it out myself using VCDS?

    Any help would be appreciated

    Rob
     
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  3. beachbuggy

    beachbuggy Well-Known Member

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    You are probably getting the same error as with the decat. Rear O2 sensor either needs to be coded out or you can put a spacer in between the lambda probe and exhaust to raise the señor out of the flow more.

    If you want to test the theory. Remove the rear 02 sensor and put the bung back in, leave the rear sensor plugged in but tuck it out the way securely and then see what happens. .
     
  4. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Mate thanks for the speedy response :)

    By a spacer do you mean like a washer or 2? to make it less inside the actual pipe?

    Yeah i can easily remove the sensor and put the bung back in to test the theory.

    When it comes to coding it out is that something i can do myself or is it a proffesional job?
     
  5. Rich196

    Rich196 Member

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  6. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Ahh cool i see so it need to be spaced out alot then lol.

    I am planning on getting my car mapped with Revo stage 2 in the nearish future once i have done my FMIC. Which i have been informed gets rid of this light too so i may well just wait for that to happen rather than buy the spacer now.
     
  7. vrbob

    vrbob Thats no Moon, Thats a space station!

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  8. Rich196

    Rich196 Member

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    Just wait and have it mapped out mate, save your money
     
  9. vrbob

    vrbob Thats no Moon, Thats a space station!

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    I take it the light being on isnt a bad thing then and does not effect anything else as its just a warning as such.
     
  10. beachbuggy

    beachbuggy Well-Known Member

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    Rear O2 sensor on all cars is just a narrow band sensor. Only good at reading stoich 14.7 . It's there as an extra to adjust fuelling post cat. You won't have any issues removing it and coding it out with mot. If you take it out but leave it plugged in it'll just read 1 the spacer movies it out of the air flow more making it less sensitive.

    Coding out needs to be done via the map and can't be done via vcds. It's literally a 5 minute job.
     
  11. Alex C

    Alex C Well-Known Member
    VCDS Map User Audi S3

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    so a faulty post cat O2 sensor will affect the fueling?
     
  12. aragorn

    aragorn "Stick a V8 in it!"
    Staff Member Moderator VCDS Map User

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    Not afaik, its only there to monitor cat efficiency.
     
  13. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Thanks for the info guys will get it sorted during the upgrade to stage 2 software. But if its not gonna happen for a few weeks i may just put the bung back in but leave it connected until i can as the light on the dash is annoying lol
     

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