Ok, a couple of days ago I got the CEL on pulled code it says P0420. No other codes pending or stored.

I did some reading that said to look at the live data from the code reader to see about the O2 sensors. I did that...and both O2 sensors on bank 1 fluctuate a lot. The first one seems to go from .1 to about .9. The second one goes from .1 to about .7.

The only drivability issue I am having is the mpg's are really low. between 11-12 with probably 75% highway (although 70 of that was towing a 2 horse trailer with one horse)

So is this an O2 that is bad...or is the o2 reading telling me the CAT is bad?

Thanks.

 

I don't have much input, other than mine threw the same code last week. I just cleared the code until I have time to get under and investigate.

On the MPG comment, I just changed my oil (Full Synthetic) for the first time since I purchased the truck in February. I have a 05 XLT SCab 5.4 step-side, and just filled up today. 50/50 driving, I am averaging 16.8 mpg, but I rarely go above 2K rpms. So it doesn't appear that mine is affecting my MPGs.

If you end up fixing the issue, post back what it was so that I know where to start on mine.

 

I had the same code about a month ago then got the sluggish symptoms with it.... Took it to the dealer the said the cat was clogged and needed replaced. They wanted 1100 for it took it to the local muffler shop and they replaced both cats for 400

 

It's the cat. You probly had misfires that clogged the cat. Look at replacing plugs, if it's that time, and replace the cat/s. Warranty is supposed to cover cats for 11 years or something, so see if you can have the dealer replace them.

 

11 yrs, is that true?

 

Did you notice a significant difference or just runs a little better?

 

As for better performance I could tell a small difference from stock. The sound also got a lot better IMO

 

I got all excited at first about the idea that the cat's might be under warranty, but I found this...

Passenger cars, light duty trucks (vehicles with a GVWR of 8,500 pounds
or less, or over 8,500 pounds if certified to light duty emission standards)
— 8 years or 80,000 miles (whichever occurs first) for catalytic converter

Although years wise I would probably be ok...I am about twice the number of allowed miles...lol.

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Can the Cats be replaced with a universal?

 

It means you've got a bad catalytic converter. I didn't want to spend money on my 10 year old truck on a new converter, so I tried this $5 solution and it worked! Took more time going and buying the defoulers than the work to get it installed. Oh yeah, rent the o2 sensor removal tool when you're buying the defoulers. It's the downstream O2 sensor by the converter. Several thousand miles and still no check engine light: