NoGraffix - No mistake on my end nor your end. JML281's code reference is a bit vague. There is reference to the Cat as well as p0240. P0420 is for Catalyst Efficiency, which seemed to make the most sense given the details in post 1 and 9. A p0240 code would most likely of experienced fuel cut from over boosting. Fuel cut is quite dramatic, and usually freaks people out, yet no mention of it. I ran with the p0420 idea since p0240 symptoms were not mentioned. I could be wrong, but I do know the difference of the 2 codes.
The big question is: what does the little piece of paper on JML281's dash say
I left the ticket in my car but I am pretty sure the code was P0240 for the cat