I took my car to a muffler shop to get a couple spots on my exhaust pipe welded, and the tech ended up removing all of the heat shields from the car. I've gotten code p420 (catalytic converter under efficiency) a few times since. I was thinking it was possible that the cat's aren't heating up fast enough and are throwing the code for that reason. does that make sense? Should I try putting some exhaust wrap on the pipes/cat's?