2004 Altima had p0420 then went away. Code reader now says manufacture code p1273

Question

Had code p0420 but went away then code reader reads manufacture code with no engine light on but reads p1273 lean code

Answer 1

Typically this is caused by a faulty front A/F sensor, however if the check engine light is not even on, I would wait until it comes on. This can also be due to the fuel trim readings being off if they weren't reset to zero after the converter was replaced.