How do you repair a 2002 Bonneville when the check engine code is Lean Bank One?

it is your 02 sensor/ bank one usally means the one before your cat. convertor

"Lean Bank One" means that the first bank of cylinders, or 3 cylinders on your V6, are not getting enough fuel to mix with the air, hence the term "lean". This is usually solved by cleaning the fuel injectors, and this is most likely your problem, because if the fuel filter or pump were clogged you would have gotten a code of "Lean Bank One" and "Lean Bank Two". It is possible it could have something to do with your oxygen sensor, and the first answer mentioned, because this sensor measures exhaust gas and sends a voltage signal to the computer telling it how rich or lean the engine is running.