The "check engine" light cam on last year around this time. I took it to 2 different dealers and they said the same error message was due to the CAT. I live in MA. I have failed my inspection & emissions to receive a sticker.

My Engine size is B5244S-Does anyone know where I can find one online or in retail stores? I'm only receiving answers informing me to purchase it at a dealer for $1,100-1,400...There has to be one out there! I need an alternative.
Thanks