Truck is throwing that code and getting terrible gas mileage. its an 03 RCSB v6 5 speed. first place i took it to told me to replace whole cat system for $1000!!!! Could it just be o2 sensors? Also what is the best way to lower it? bags? eibach springs? thanks guys

 

It's been awhile since I worked at the parts store, what is the description of 420 again?

 

the code is for emissions and the entire exhaust system SOMEBODY HELP!!!!!

 

i might be mistaken but i believe its for the cot (catalytic over temp) protection if u removed ur cats u need to raise that to the max which i believe is 1200 with a tune or a diablo will do it.

 

Googled your code: http://www.obd-codes.com/p0420

 

If the O2 sensor is giving the correct signal, your cat on bank 1 (driver's side) is no good and will need to either be replaced, or gutted and the rear O2's turned off (not exactly legal, but improves exhaust flow lol). That code is basically saying that the cat isn't doing it's job

If you're planning exhaust upgrades in the future, now's the time to get the PCM tuned and take care of the cats.

 

There could also be a pre-cat exhaust leak. Happened on my truck, and on my Mom's car.

 

As to your lowering Q, just do a search / separate thread. Keep it more to the specific forum & you'll have better response. Just handle the o2 stuff on this thread. Just my .02.