what does these 2 code definitions mean?
on 2011 Buick Regal

Catalyst System Bank 1 Low Efficiency
and
HO2S-11 (Bank 1 Sensor 1) Circuit Low Input

Thanks in advance for any help given.

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3 answers
You gotta check out the o2 sensor output + wiring etc on bank 1
Google it of utube tell you how to go about it..
check with the dealer could be still under warranty
warranty on emissions is 7yr 70k miles