My brother was reporting his car keeps going into limp mode while i was away. He never pulled the codes for me or anything else but he took it to the dealer Saturday.

They called back saying that he needed a new catalytic converter. Now mind you it has a MPx catted DP which i dont think they even knew was aftermarket from the way he was telling me they wanted to replace it under warranty

My question is this, can the O2 sensor cause limp mode? He said he wasnt seeing over 5psi and it was popping a lot. The car had been doing it randomly over the past month and apparently now it just wouldnt go away.

The DP has been on the car for almost a year now. I really want to lean toward the GMS1 causing his issues as i feel the car has never been right since the GMS1. Although he is luckily listening to me finally and having the wires soldered.