How did YOU fix your p0420 & p0430 codes

I have bought a used 2006 Tacoma TRD and have had pretty much every dash light stay on, including airbags, TPMS, and engine. I have managed to get them all fixed except the check engine light keeps coming back on. The prominent codes, that mostly come on together (once one was pending and the other active) is p0420/p0430. (Sometime p0441 Evaporative Emission Purge flow and P0455 Evaporative Emission Leak come on too)

Although there might be a relation between the p0430 and the evaporative emissions, I am wanting to fix the p0420 and p0430 first. I have done a fair amount of reading, and answers seem to be all over the place. People have suggested it is bad cats, but also suggest that the way to check them is to see if they are hotter on the outflow and if they are, they are good. My front Cats are both around 300 on the engine side, and 500 on the exhaust side, so, based on that, they appear to be working. I have seen these codes attributed to bad grounds, gas, O2 sensors, fuel pumps, pvc valves.

So since this appears to be a reasonably common code, I was wondering, if you have it, how did YOU fix it? Any input is appreciated. TIA.

 

I'm no master mechanic and I'm sure other folks here will have much better suggestions, but not long ago I did some work on my truck and it was sitting for some time. After hooking the battery and taking it out for a spin my OBII scanner was showing the CAT and O2 sensors categories as failing with a PO420. Also had an EVAP leak showing up. Now, these problems were probably just there because I hadn't driven the truck long enough after the battery reconnect, but I ran some Cataclean through it anyway and the codes went away. It's supposed to clean your CATS so long as they are just dirty and not bad, and your O2 sensors as well. A cheap enough thing to try. Of course, it is worth noting that I also recently had several exhaust leaks close to the rear 02 sensors so that probably didn't help anything either. You can test for leaks in your exhaust by hooking up a shop vaccumm to your rear tailpipe while the truck is off so that it is blowing air out (into the pipe I mean), then taking a spray bottle with dish soap and water and spraying it over your exhaust connections while the air is flowing through everything. If you see bubbles start to blow up noticeably where you sprayed, you have a leak in that location. Check out the Chris Fix video on YT for a better explanation on how to test and patch such areas if necessary. Can be done on the cheap. Point being an exhaust leak can also mess with the readings of your 02 sensors in certain cases. Also, you can easily run a basic test on your 02 sensors with a multimeter just to make sure you get a reading. Plenty of info on YT on how to do that as well. Of course, there is a more thorough and complete test for 02 sensors which involves removing the sensors altogether from the truck, but that was way too much work for me. If you just suspect bad gas, a can of seafoam might not hurt and fill up with quality gas next time. These are some simple things I have done on my truck in the past that you could try.

 

Replace the gas cap.

 

Are you having any trouble getting over a certain RPM while driving? Can you hear any rattling from the cat? Do you have a crack in your headers?

The evap code could be any number of things ranging from needing a new fuel cap to needing to replace fittings on the evap system. Diagnosis of that is best done by a shop who has a smoke machine for that. Not sure about Toyota, but GM had a big issue with the fuel sending units rusting out around the lock ring and causing evap codes in the late 2000's.

 

Bought a dorman cat off of rockauto for about $250 6 years ago. No problems since.
Took the OEM cat to a local scrap guy, he looked up the numbers on the cat and it falls under a category called "low grade foreign"
Failed just past the warranty. Thanks toyota!

 

Thanks. This is a fix for the evap codes, not for the p0420/p0430 I am guessing? I will look into that. Appreciated.

 

No. And the truck is driving well. I am getting 11.5l/100 or about 25 Canadian MPG.

 

That leads me to believe your cats are fine

 

Well I went and put two new Denso downstream 02 sensors (part number ending in 60 is right and ending in 61 is left???Seems counter-intuitive). I have only driven it for 20 miles but so far no codes live or pending. It is looking promising.

I too think my cats are likely fine as the truck has only 160,000 miles, and they were 200 degrees hotter on the downstream side.

 

I had the P0420. It turned out to be the gasket connecting the cat to the Y pipe. Gotta replace both gaskets as it's not coming apart otherwise. Look for soot around all the joints.

I used a ratchet strap at the Y and the rear axle to pull the exhaust back. Worked like a charm.

 

Go where the weather is the roughest and check all the hose clamps on the fuel tank fill hose and other related hoses. Also change the fuel cap. Do not use a locking fuel cap

 

I contacted Underdog Racing Development URD and got an O2 simulator module that keeps the code off. But that was on my 2000 4Runner. However, they do make them for the Tacoma, and just about anyone running headers and high flow cats or no cats, have one of those O2 simulators and they work flawlessly.

But in your case, before doing that, replacing the cats is recommended.

 

Another good tip!!!

 

Thanks, but since my cats don't show any sign of deterioration that I could determine and are 200 degrees hotter on the downstream side, I tried just replacing both O2 sensors, and it seems to have worked.

I posted because I had conflicting information. Some posts said that if you have both codes p0430 and p0420 at the same time, your cats need to be replaced. Other posts said that if your cats are much hotter downstream than upstream they are fine. It appears from my being able to fix the codes by replacing just the 02 sensors, (as I THINK has happened), that cats are not always the problem when someone has both codes.

Intuitively this makes sense. Since the codes can be triggered either by bad cats (right or left) or bad 02 sensors to check the cats (right or left), getting both codes could either be the cat is bad or the sensors are bad. Having both together doesn't tell you that it is the cats and not the 02 sensors. Additionally, it could be leaks on both sides. Lean fuel on both sides (possibly fuel pump) or other issues that are effecting both sides.

Hope this helps someone in the future. Thanks to all who replied.

 

I chased this problem for several weeks on my 3.4 and went through several sensors.

Ended being a bad cat, it had 230k on it. So even if they are the proper temperature, the sensor range may be effected because the internals have deteriorated. Depends on what kind of gas was run through it and how many miles it has. Dont be surprised if you need cats, if the vehicle has over 200k miles.

Because I replaced my cat with a high flow cat, I still got the p0420 code so i had to get the URD module to fool the computer into thinking the voltages are right. I’m sure it wont pass an emissions sniff test, but I dont have to work about that where I am just yet.



I hope you got it figured out for cheap though!