i got a check engine light and when i checked the code im getting P0420 catalyst system efficiency below threshold (bank 1) what does that mean exactly? im thinking a bad oxygen sensor. any help is appreciated thanks.

 

It sounds like yourcat on bank oneisn't working properly. If your 02 sensor was bad it would give you a code saying so. If your cat isbadit won't let exaust flow properly, and won't work "efficiently" I would either check it out myself, or have someone who knows check it out for you. Sometimes if you run rich for a while, the excess fuel will get into the cat, and mixed with the high temps inside, and melt the honeycomb inside, thus working below efficiency threshold.

 

It could still be an O2. Check the voltage. Make sure it's switching back and forth from around .1V - .9V and even if it is, it still may be bad.

 

changed out all the o2's and so far seems like the problem is gone. hope it stays gone.