Built in response to the Chevrolet Blazer, Jeep Cherokee and Toyota 4Runner, the Pathfinder was Nissan's bid to capture a bit of the sweet mid-sized American SUV market. It might be a soft-roading "CUV" now, but in its first- and second-generation heyday, the Pathfinder was a dirt-road fiend with the throbbing heart of a sports car.
This code reads as "catalyst efficiency below threshold, bank one." In English, it means that the second oxygen sensor in the Pathfinder's exhaust system has noticed that the Bank One catalytic converter -- the passenger-side converter on V-6 models -- isn't working. Possible causes include a broken or "poisoned" converter, engine misfire, a leaking exhaust manifold or system, vacuum or intake leaks, bad spark plugs, a bad computer control module and faulty or clogged fuel injectors. Bad rear O2 sensors will occasionally throw a P0420, but you'll generally also get other codes specifying an O2 sensor failure. If you get this code all by itself, odds are best that your converter is shot.
