Was looking for a bit of advice on what action to take for an engine code error: P0420 - engine light is on permanent but car seems to run fine - I have a Vgate pro OBD2 interface with the OBDll auto doctor app. Is this the best app to use and what would I be looking for in the live data readings etc? With a paid app I assume I can rule out certain issues and/or slim it down to, or maybe even pin point the exact problem? The only time the alarm come on is when the engine is nearly at normal running temp, once the alarm is cleared, the alarm remains off, can you please advise
