My wife's van has started throwing a p0420 code every few days recently. I replaced the plugs, wires, and upstream O2 sensor. I used an ACDelco brand sensor, and the code came back a couple days later. I've since read you should only use the Mopar sensor. Is it worth popping for another new sensor, or just go with an O2 extender to try to make the code go away? In my experience, ACDelco sensors have been quality, but could it be negatively affecting gas mileage?

 

The only brand I'm aware of to avoid is Bosch. From reading a 420 code is often caused by a bad cat converter and they have an 8 year 80K mile government warranty.

 

That expired almost 40,000 miles ago.

 

Update: The code went away after installing a new cat (Magnaflow).

 

Good news. Thanks for posting the fix.