So for a few days all was well.

Today the CEL popped on so I read it and it spit out P0420.
Catalyst System Efficiency Below Threshold (Bank 1)


I think the cat's dead, what say you? Also, when I was under there doing a starter and the sensors, I noticed the converts on both sides don't match. Is this normal? Both were badged Rover on them Factory replacement on one side perhaps?
Anyone had any luck with Magnaflow cats? Are they enough to satisfy the car's OBD system?

 

do a lot of research on this one. replaced the front and rear o2 sensors on my wife's car, then I got that code.

wasn't the cat. bad rear o2 sensor.

 

This is normal. There just isn't as much room on the side with the flatter, lower profile cat.

 

To rule out the cat swap the "bad" O2 with the new one and see if the code follows.

Yes the OEM cats are not the same on both sides, space issues.

 

Would an exhaust leak pre cat on aformentioned side do that? I believe the leak is on that side.

 

Yes a big leak pre-cat can set off a code.
The ECU knows how much exhaust their should be, if its wrong...code.