I have a 2012 dodge charger R/T 5.7 rear wheel drive with 140k on the miles. No clue about the transmission and dont know how to find out.

. I have ran the codes many times bc it won't let me use the remote start with any lights on. But my oxygen sensor is the code I can't get off. I went to oreillys and got 2 different brands and put those in. Didn't change anything. Then finally just went and got a oe one and that also didn't fix it.. someone had stated that it could the Catalytic converter that could make that light come on? Any ideals that I could try at home? Don't have lots of money to just throw at this car. 😒 

Thanks to everyone in advance