P0420 - seems eventually it's the Cat. anytime anything else?

I've been dealing with a P0420 for a month now. My
04 Prius has 240K on the clock and it's been driven a bit roughly by a construction worker. That being said, when I drove a way from the fellow I bought it from the CEL popped up and now I owned it. oh well.

I've been thinking about a solution to the problem with a bad cat. There are basically three parts to the problem with a few other little bits tossed in. First is the Upstream O2 sensor, the Cat, and the downstream sensor. Also a little bit of extra air slipping into combustion chamber or a bit of oil getting burned will contribute to the problem.

A p0420 tells the operator that the cat is dead. Somehow I do not believe my cat is dead. Maybe a sensor, but not the cat. If the cat were dead, then it would be clogged and the engine would bog down and acceleration would be horrible. Thus, I believe the cat is still functional, yet not dead.

Now, onto the sensors. If the upstream sensor were bad, it would/might give inaccurate data to the pcm. I watched a YouTube vid of a prius with a dead cat and the tech using a computer to see the graph of both O2 sensors. The upstream sensor was bumping up and down(which is normal) while the downstream cat was doing the same thing(it should be a straight line going across the graph). The tech then changed out the cat and it fixed the problem. The downstream O2 sensor was now flat lining. So this tells me that the upstream sensor has a set value and the downstream sensor must have a different value. How to get the downstream sensor to have that differing value? New sensors, new cat, tighten up air leaks, or...…….clean the cat somehow.

Onto cleaning the cat....I've seen youtube vids where folks soak their cats in differing types of liquids in order to scour the build up off the honeycomb areas. To me, that seems like a good idea expect it would mean taking off the cat and then finding a way to soak it. Too much work for me. So I decided to go a different route to clean the cat. On a thread somewhere within PriusChat a member stated that with each fuel tank fillup he would add a bottle of Techron. After six applications, the P0420 went away. I became interested in this way of cleaning the cat so I began doing the exact same thing. First tank filled up and a bottle of Techron was added. Second tank was the same. Now comes the third fillup and I could NOT find Techron at the gas station so I used Lucas engine treatment in the small bottle. I've put about 50 miles on this tank of gas and when I went to start my Prius after work tonight I noticed the P0420 light was out. All the way home I was thinking the light would flick back on, but it stayed off. So maybe the Lucas is the cleaner my cat needed.

Each tank of gas lasted about 325 miles and the amount of gas added was 8.25gal and 7.00gal. So after about 700 miles my cat light went dim. I'm tentatively happy and hope the light stays off. Cross my fingers

Also I made sure I tightened up all the intake manifold joints, added Mobile 1 syn oil 5w30, also some MMO in order to lube the rings. The plugs looked good, but have a lot of miles on them.

So, in summary, for the price of two tanks of gas, two bottles of Techron, then a partial tank of gas with a bottle of Lucas engine treatment I might have solved my P0420 problem

Hope this helps somebody.

 

Can you please link to that thread here?

Thank you.

 

This type of cleaning will be very disappointing when the light comes back in a few days

 

SFO, I'm trying to find the link but I come up with NADA. Sorry. But I do know I saw it on this website.

JC91006, you might be right, but I certainly am at least temporarily happy. Feels good after all the disappointments in my life lately.

 

We had a member that used an acid solution to clean it (on YouTube), worked just enough to pass a smog check and the light returned.

 

Well, all good intentions go to waste at times. Seems that I wrote a long diatribe on what I thought was a good solution for a common problem only to smack my self in the face when the CEL popped on again. T'was then that I had remembered that I disconnected the negative battery cable to fiddle with my cruise control and clock spring. My "wonderful" solution truly hasn't kicked in yet. Only a reset of the CEL. Maybe if I'm lucky in a couple more tanks of gas my idea will come to some sort of good result. In the mean time, know that I'm still waiting for a positive result. UGH!!