P0171 - System to lean (Bank 1)

[Robbks]

as i noted before, it could be a dead o2 sensor,
but an exhaust or intake leak could fool the sensor.
aswell as dirty injectors.

but an OBD scanner should be able to see what's going on with the sensors
have a look and listen for leaks (piece of garden hose as a stethescope and probe around exhaust/ intake joins)

Too many technicians these days hook up the scanner, see it's thrown a code for a sensor and just replace it and send send you on your way.
only for the problem to re-appear because there's another issue causing the sensor to read outside it's normal range