2008 BMW M3, 125,000mi, the ODB Readiness monitor for the O2 sensor won't become ready. I replaced the two post-CAT O2 sensors and I'm still seeing the two sensors disagree. One is showing rich and one lean. Occasionally they will sync up while driving, but at idle they always disagree.
The only pending code is for Secondary Air Flow Bank 1.
Next step? I'm thinking about replacing the upstream sensors. Does the Long Term Fuel Trim indicate an issue with the upstream sensors?
Might be hard to read but O21x2 is 0.7V and O22x2 is 0.1V.