Engine light on code P0420 catalyst effientcy below threshold changed both 02 sensors cause and how to correct car still runs great and no smell?
This engine code can be triggered by any one of the
1.) The catalyst in the catalytic converter is cracked, clogged,
or otherwise damaged.
2.) The secondary O2 sensor is malfunctioning.
3.) There is an exhaust leak.
4.) The computer unit is faulty.