I just purchased a 2004 Nissan Maxima SE 3.5l and ran great until about a week ago. Engine light came on, checked codes are p0726, p0128, p1800, p0420 and this is after replacing the coils and plug which was issue last weekend. I need advice on what I should replace sense it's multiple possibilities . Please help.

 

What are your symptoms? How is the car behaving?
And why did you replace the coils and sparkplugs? And did you install OEM coils, or aftermarket? What sparkplugs?