I'm looking for the most likely solution to P0171 and P0174 error codes. Most likely the air pump but how can I prove it? The error reads lean on bank one, and lean on bank two. I'm guessing the pump has gone bad but not sure how I can know for sure. Also I've been getting random P0734 codes, which show wrong gear ratio in gear 4. I clear it and it comes back days or weeks later. I suspect something with the rear axle but not sure where to start looking.