The 420 was probably posted before the O2 sensors were destroyed. Post failure and reset, the CEL would assuredly have come on, but with a different code.

 

Just this day replaced a cat system on a Volkswagon.
The rear sensor moved with the front when looking at it with a Scanner, setting an efficiency code.
The cat was not plugged but just gave up for whatever reason since I don't know the car's history.
Looking at the system right after startup with the new cat showed the rear sensor was stable while the front hunts, as it should do.
Just can't fool the system design no matter what or how it happens.
Job complete.

 

You got to love the scanners that will graph in real running time the PID's. I recorded 10 frames of mine while running about 60 MPH with everything warmed up to operatin normal temps for future references if I have a problem, in my pictures. LOL

 

The truck is fixed! All is well now.

The front cat disintegrated and plugged up the back cat. Completely obscuring the entire exhaust flow.

I tried to back out the upstream O2 sensor so I could limp the truck to the repair shop. Yeah, that did not happen. I destroyed the O2 sensor trying to get it off. Heat, special wrench, PB blaster.. Nothing.

So this morning, to make the trip to the shop I enlisted the help of my saws-all and did this



And proceeded to drive to the repair shop.

Every thing is fixed now, the pip was rebuilt, the o2 sensor replaced, and a "single big cat" replaced the clogged mess.

Now, my truck runs better than ever, pulled my travel trailer tonight, and it was like a freight train.

I am very well pleased.

Thanks!

Jerem

 

Oh, a custom-calibrated exhaust vent! Cool!

Glad that you got it fixed, and that you let us know how it worked out.

Your engine and exhaust valves thank you!

 

Sawzall & Cutting Torch are the tru tools. " LOL "