Can a bad spark plugs problem in the Odyssey cause the catalytic converter to fail?

Hi, to answer your question -- maybe. The spark plugs were likely replaced due to oil fouling and an extended warranty applied due to a service bulletin that covered 4 of the spark plugs. I'm guessing that you had the pistons and rings replaced in those 4 affected cylinders as well, while the timing belt and water pump was also replaced for maintenance. This is not abnormal. Depending on how long you drove with the "check engine light" and misfire concern, unburnt fuel may have passed through the exhaust including the catalytic converter. If this happened, the cat would get excessively hot and become damaged as a result. It's hard to say if this happened, but it's worth going to your dealership and lobbying for assistance. If you tend to be loyal to your dealership for service visits and bought the vehicle new, you may be able to obtain assistance from American Honda for the catalytic converter repairs. It's worth a shot to speak to the service manager of the dealership you work with. Good luck.