I just bought this 2013 avenger from my daughter. It was abused previously. I've been cleaning it up. At one point the 1 and 2 coil packs have gone bad. And already had the downstream O2 sensor go. But it still threw the P0420 code. So today I finally replaced the upstream O2 sensor. I did some driving but while on the freeway, on cruise the P0420 came on again. I'm afraid of the cat having gone bad from the coil packs. Is there any way to find out for sure. I have a code reader and keep clearing the code. It's the only one that comes up.