P1276 2004 Nissan Sentra -

Question

I changed the O2 sensor and the mass air flow sensor engine light comes back on now what?

Answer 1

after replacing it did you do the Clear Mixture Ratio Self-Learning Control Data? if not see link below

http://nissanhelp.com/diy/sentra/projects/nissan_sentra_clear_self_learning.php

if the Clear Mixture Ratio Self-Learning Control Data  did not help 

The other things to check are 

- Intake air leaks

- Fuel pressure

At idling: Approximately 350 kPa (3.57 kg/cm2 , 51 psi)

- Faulty Fuel injector