i got a P0151 code showing which is a low voltage from an O2 sensor

also a P1151 which is a lean running cylinder bank, i know this the sensor is the first one on bank 2

what do you guys think i should do, i've been driving the car for a month with these codes apparently and haven't had any probs and seem to have the same power but less gas mileage which is weird cause the code says it's running lean?

 

i would inspect the o2 connector and wiring for damage such as chaffing and corrosion. also inspect your air intake and manifold for any vacuum leaks and that everything is secure. if that is good. i would think the sensor may be at fualt. but i would try disconnecting the battery to clear the codes and see if they come back.