Rich means there is too much fuel going into that bank. The computer will have tried to cut fuel over time to compensate, but it is no longer able to do that physically.

There is either not enough air getting into the engine, or more likely, something wring with the fuel delivery system, and it is leaking down too much fuel. Because it is effecting both banks, I would guess something like fuel pressure regulator as opposed to something one cylinder specific like an injector.

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2001 E53 3.0 5pd