My daughter's EX coupe quit on her last week. She said the car began to lose power after about an hour of driving then quit all together. I had the car towed home. A few days prior to that the CEL came on and we got a 0420 code for cat efficiency on bank 2. and a MAP sensor code and a heat circuit code for the downstream oxygen sensor on bank 2. I had purchased the sensors and was waiting for the cat to be delivered. Wished I had not let her use the car. New cat was delivered the day she broke down.

I dropped the exhaust today and pulled all three cats. Bank 2 (radiator side) was toast and broken up with chunks of innards in the exhaust pipe. Bank 1 Cat looked OK. Honeycomb was clear, Cat 3 downstream fro 1 and 2 was plugged with the remains of #1. Completely plugged.

I am curious if any engine damage was done during this failure. Plugs looked normal and I did not get to do a compression test today. Have had the old tailpipe cats go bad in the past but this is my first car with warm up cats acting as exhaust manifolds. Sorry for the long post but its my best description.
Anyone with experience with this in the past?

 

I personally have not had this happen to me but do know of others where this has happened.

Once replaced you will want to very everything is checking out - no codes. If you have a scan tool that can read fuel trims you want to check those as well. One of the big factors that will cause a cat to go bad is too much fuel being passed through it.