Code #P0421. Please help.
#4
I couldn't really find any. The only way I know to test if it is the sensor is to get a new one, and those are expensive on their own. Can you see if you Cat is glowing red? if it is then is probably the cat and not the sensor and viceversa.
#6
Not all the times they emit that smell, this is actually the first time of someone mentioning that. But I still wouldn't discard it, the O2 sensor is cheaper so I'd go that route too. As far as I know Bank one is the passenger side if you're in America, the driver side if in Europe or Asia.