Q: I just replaced all of my 02 sensors on my 2011 300c and a few weeks later boom! Check engine light on again.

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I used YourMechanic to have my upper and lower/downstream o2 sensors replaced. The lowers were the most recent about 2 weeks ago. Needless to say the check engine light came on the day before yesterday. So I hooked it up to my scanner and The code P2271 on B1S2 popped up again stuck on rich. Which is frustrating after just having it fixed. I'm mainly just concerned that there could possibly be something else that is causing this o2 sensor to go bad. Like possibly a bad CAT converter or vacuum leak. So any thoughts would be appreciated. Thanks.

My car has 70000 miles.
My car has an automatic transmission.

It sounds like you may possibly have some other condition causing the motor to run excessively rich and that it was not the O2 sensor that was faulty. This is rare, but is definitely a possibility. Things like leaking fuel injectors, a bad fuel pressure regulator or a dirty or faulty mass air flow sensor may all contribute to a rich fuel condition resulting in the catalytic converter not being able to perform its function properly. I would suggest having a professional from YoruMechanic come to your location to diagnose and repair this.

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