Code P0420 may mean that one or more of the following has happened: A damaged or failed oxygen/O2 sensor downstream oxygen sensor wiring damaged or connected improperly. The engine coolant temperature sensor is not working properly damaged or leaking exhaust manifold, catalytic converter, muffler, exhaust pipe. Failed or under performing catalytic converter, retarded spark timing, leaking fuel injector or high fuel pressure cylinder misfire, oil contamination. Not all codes will set a check light, most probably caused by a failed cat converter. I would be looking here first and then if that is okay, continue with the inspection of other components as listed.
Monday, December 4th, 2017 AT 4:26 PM