High NOx emissions can occur when an engine's air-fuel mixture is too lean. ... This could be caused by a problem with the vehicle's oxygen sensor, malfunctioning air flow and coolant sensors or a leak in the fuel system. They obviously have limits on how high NOx emissions can be..
Mark Tierney DieHard NSW JZZ30 GTT-L Built 1.5JZ Beast, UCF11, IS250, GS350-FSport, Ducati SS