P0012 engine code

[Ramon1691]

Hello Yaris world I'm having a code in my Toyota Yaris 1nzfe engine p0012 camshaft over retarded bank 1 I'm stressing over this the car has 147000 thousand miles the previeous owner didn't keep up with maintenance that well, car runs fine a little roughy idling at times and sometimes it takes a few cranks to start I did a whole tune up on it when I bought it 3 months ago like I said no issues driving it I did some research on the matter it appears it can be as simple as a solenoid like the oil control valve or the camshaft gear code got erased after installing new battery a month ago it hasn't come back my mechanic says to wait until it comes back to take it in my question is hat could be causing this issue? If it was serious shouldn't the check engine come back right away?