HFC p0420 code check engine light help!

[bbova1]

Hey guys…I have a 2013 b8.5 Audi A4 2.0T with a apr stage 1 and a USP HFC. Keep getting a p0420 Catalyst System Efficiency Below Threshold Bank 1. It comes on after 10-30miles. I tried to clear it and pass inspection but failed.

Anyone had any successful emissions passes with a 02 spacer or something similar? I may swap out the 02 sensors but not thinking that’s going to do it. I read 2013 having more issues than the b8 up to 2012. Hoping to find a needle in a haystack here.

Any help would be great!


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[beatsageo]

You need to alter the reported voltage from the rear O2 sensor, not sure what the legality of this is in NY so exercise caution. The readiness monitor will continue to fail if you replace the O2 sensors. Removing the presence of O2 for the rear sensor will also get you there.

[JLAllroad]

Hey guys…I have a 2013 b8.5 Audi A4 2.0T with a apr stage 1 and a USP HFC. Keep getting a p0420 Catalyst System Efficiency Below Threshold Bank 1. It comes on after 10-30miles. I tried to clear it and pass inspection but failed.

Anyone had any successful emissions passes with a 02 spacer or something similar? I may swap out the 02 sensors but not thinking that’s going to do it. I read 2013 having more issues than the b8 up to 2012. Hoping to find a needle in a haystack here.

Any help would be great!


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It will only work with the stock catalyst, APR tunes are emissions compliant, your HFC is not.

There is no known combination of spacers/elbows/mini cats that work on the B8.5.


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[Slow_Q5]

This is really random, and highly doubtful it will yield anything tbh. But I have heard of using a spark plug to spoof it.
i do not know if this:

You need to alter the reported voltage from the rear O2 sensor

would be the end result.