The check engine light was on so I got the diagnostic test done. Came back that "Upstream Bank 1 is burning lean." So I switched the O2 sensors and got it checked again. Said that "Upstream Bank 2 is burning lean." Replaced Bank 2 O2 sensor with a Bosch. Check engine light came on again. Got it checked out again and it now says that "Upstream Bank 2 is burning rich." I got a Ford OEM O2 sensor and replaced it. Now just waiting to see if the check engine light will come on again. So my question is are the O2 sensors compared in the ECU or is the Bosch not a good replacement?