I have a 2006 Mitsubishi Galant 2.4 liter 4 cylinder car.

Question1:
How many oxygen sensors does this car have total?


Question 2:
I recently got OBDII code P0431 witch says its bank2 sensor or catalytic converter. i would like to try to change the o2 oxygen sensor first but i dont know witch one to replace. Facing the front of the car I see 4 sensors, i see 2 (one on the top and another on bottom) on the driver side of the engine....and i see another 2 (one on the top and another on bottom) on the passengers side of the engine. which one(s) should i replace?

any input or feedback would be greatly appreciated