Does any one know where this o2 sensor is

I have a scanner which picked up a code in my 97 blazer it says sensor 3 of the o2 sensors is bad does any one know where sensor 3 is?

I have a scanner which picked up a code in my 97 blazer it says sensor 3 of the o2 sensors is bad does any one know where sensor 3 is?

Well codes do not say 02 sensors are bad.
They say check thing out. :grinyes:
What engine and what is the code no?
Sensor 3 can be found on the rear of cat.
mt

P0420?

sensor 1= in y-pipe after drivers side manifold
sensor 2=right before the cat i believe
sensor 3= after the cat and before the muffler