2004 tahoe - Code P0430
 

Engine light came on. I connected an OBDII code reader to it and it came up with P0430.. Is this an O2 sensor? If it is where is/are they located?

Google is ur friend: OBD-II Trouble Code: P0430 Catalyst Efficiency Below Threshold (Bank 2)

Given the age of the vehicle its possible the code is correct... bank 2 will be the side that cylinder 2 is on... there will be one before the cat and one after I believe sensor 1 is pre-cat and sensor 2 is post-cat...

I would follow the link Shark posted as it is a good flow to use, check for leaks..etc