Warm Up Catalist Insufficent In Bank 1 P0421

Mitsubishi is a troublesome vehicle to most owners, but a cat coming on line "late" is usually dying from contamination from either running very rich (prolonged missing cylinder(s) and/or ignoring a CEL .... or from and engine that burns oil and wasted the cat. Mitsubishi was one of the first companies to build cats with "wire explosion" coatings that could not handle minor contamination of their catalyst beds. Hence, when other manufacturers found they could save $$$s by the same wire explosion coatings, then lube oils had to be reconfigured to "LE" oils that removed critically needed lubrication additives. In general..... LE oils cause a lot of untoward wear to older engine designs. There's always the possibility that the cat was changed for a used one, since a new or rebuilt one for the BIG THREE "M" cars (Mercedes-Mitsubishi-Mazda--- that charge exorbitant prices for their parts) was too expensive for someone to replace prior to selling their car. In my book, look for another car.