I have had CEL come on during in town driving I have checked for air leaks and could find none. I understand it could be an O2 sensor, I do not see a rear O2 sensor on my car and the air intake temp sensor is tight. I understand the the CAT could also be bad but I also understand that the CAT do not go bad very often. The car has 230000 miles on it.

 

Hello P0422 "Main Catalyst Efficiency Below Threshold (Bank 1)". At 230,000 miles I wouldn't be surprised if your cat was dead. Too bad trial and error is so expensive-even DIY with junkyard parts. Kira