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2011 CTT is 500 miles into replaced cam adjuster fastening screw per recall and getting this and same for Bank 1, which is code P0421:  



• Catalyst 1 Efficiency Below Threshold Bank 2


Any thoughts?


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Have you tried clearing it and seeing if it returns?

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Yes. There is a very brief but noticeable drop in power, like a rough idle,  just b4 check engine light goes on. Seems to resume normal operation thereafter but light remains. 

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Have you checked for an exhaust leak between the engine and O2 sensor behind the cat?

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Will do and report back. Thank you. 

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Posted (edited)

This is very likely the result of the cam adjuster failure.  I almost guarantee that the side you're getting the cat efficiency fault on is the side that the cam adjuster failed on.  When the adjuster fails it pushes all kinds of fuel and oil into the cat in some cases (albeit fairly rare cases) and fatally damages the cat.  Hopefully you're still under 7 years/70,000 miles and get covered under federal emissions warranty and if you aren't hopefully you have a good relationship with you dealer and they can push for coverage through Porsche.


Whoops just reread your original post and noticed you didn't have a failure, you just had the campaign completed.  In that case the cat is probably just bad.  Exhaust leaks are very rare on these and nothing done under the campaign would cause this fault

Edited by PTEC

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