Subaru Forester check engine code P2097

The check engine light on my 2006 Subaru Forester with 92,000 miles came on recently. A scan revealed the engine was running lean. After three more trips the mechanic determined the rear O2 sensor was bad and replaced it. This was the only part replaced. Now the computer is sending code P2097; Post Catalyst Fuel Trim System Too Rich Bank 1. I have read it could be anything from the catalytic converter needs replacing to “resetting the adaptation values.” Any suggestions?

I wonder whether the AF sensor (that’s the heated O2 sensor that’s in front of the CAT) is bad.
Your mechanic should be able to read the actual levels and make that determination.

Was the rear sensor replaced with OEM or some after market sensor? After market sensors are not always the way to go…

I’ll have him check the AF sensor. I am assuming that the rear sensor was replaced with an OEM as this mechanic always recommends using original Subaru parts. Thanks.