Do you have a proper BNW dedicated scanner? It would be good to post the code description as well. There often is no easy answer to mixture related codes which is often the reason the car gets traded off in the first place. If the codes are actually for the oxygen sensor or circuit itself that is different than a mixture code. What do you mean by "powered vehicle" ??

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)