where is my 02 sensor located

Just because you have a p0420 code it does not mean you have a bad downstream O2 sensor. Most likely it is a bad catalytic converter. Someone needs to monitor the signal from the downstream O2. When the engine is wram up the downstream O2 sensor cannot mirror the upstream O2.

Answer #1 is correct. The Bank 1 is the front cylinder row, near the radiator. The #2 sensor - which measures the cat. efficiency is the sensor after the CC, towards the muffler. If you have less then 80,000 miles the CC is covered by the 8years/80K miles Federal Emission Warranty. Zee