Codes P0140 and P0171, engine lamp is ON. on 2011 Mazda Mazda2

My Mazda 2 2011 (skyactive, istop) is showing fault codes P0140 and P0171 when diagnosed.
P0140 - O2 Sensor Circuit No activity detected( Bank 1 sensor 2)
P0171 - System too Lean (Bank 1)

1 answer
should be under dealer warranty