How many miles on that 2004? Do you have problems with oil consumption? Have you had any problems with misfiring, lower gas mpg, anything else that might be relevent? P0420 is catalyst below efficiency, meaning that you have a problem with your catalytic converter or A/F sensor or downstream O2 sensor. Mechanical problems with the converter are almost always due to a prior or concurrent engine problem. But they are dirt cheap, probably cheaper than what you paid for that new MAF sensor. Walker, Eastern make bolt-right-up cats for less than $200 for the 2.4L.
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