Hey everyone my son’s 99 Canadian SI coupe had a plugged cat when we bought it in Oct 2023. Put in a magnaflow cat. Was fine for a while and then recently started to rattle from inside.

we had some issues this week throwing code p0131 for the primary o2 low voltage making it go into limp mode.

we did a tranny drain and fill, new fuel filter and punched out the cat to get it going so far it runs great.

my question is what would cause the cat to break down like that? Never had any misfire codes so I am confused. Everything I read about them rattling inside is due to misfire and the raw fuel heating up and melting the cats guys.

 

Low quality. Aftermarket cats aren't even close to the quality of the OE cat... and failure rates happen much more often with the aftermarket ones.