Trouble code issue

so ive been having a code pop up for awhile now and i cant figure out what the fix is. its a low voltage code/ below threshold code for the driver side post cat o2 sensor (im getting the code pulled tomorrow didn't have time today) I've changed the o2 sensors out and cleaned the maf sensor and it fixed it for about a week and then it came back on. I've got a catted mrt h pipe ,magnaflow catback and a jlt ram air intake but besides that its stock engine wise what do y'all think is causing this?

low voltage can be caused by alot of things. bad ground. damaged wires etc. gonna have to do some wire hunting.

ive been looking havent found any yet the thing that gets me though is it happened about a week after i put my h pipe on. didnt have any problems with it before. could it be the o2 sensor itself? i didnt get a ford one just the replacement one they had at advanced.

Ive heard bad things about the non-ford sensors. Always been told to stick with motorcraft. Oreilly sells them.

will be getting a motorcraft one in the morning since i finally have some time to work on it.