P0420, 78k miles 2.7l, Failed Exhaust Donut Gasket - Solution

I had a P0420 code pop up. This Tacoma has 78,000 miles and has been well taken care of, 5k mile oil changes etc…


I did some basic research, including on this forum, and came to the conclusion that this code isn’t a sensor problem. It means your cat is bad, unless there is an exhaust leak between the cat and engine block.


I hooked up a shopvac to blow into the exhaust, and got tiny bubbles around the donut seal (figure 1). I was skeptical that this was the problem. These bubbles were really small and the shopvac puts a good deal of pressure in the system. (Turns out it’s enough to throw the code).


I ordered the Felpro 61106 donut seal, and installed it with new Dorman bolts and springs. This leaked even worse, huge bubbles coming out fast. The Dorman is dimensionally different than the Toyota seal (figure 2).


I went to the dealership and paid $55 for the Toyota seal. I pulled the cat totally out (figure 3) and cleaned up the mating surfaces on both ends with a wire wheel. (The bolts had to be cut off the rear joint, replaced them with ⅜” bolts from the hardware store and a Felpro seal). Figure 4 shows the surface after cleaning. The surface is marred by the old donut and has deep scoring.


I applied nickel anti-seize to the mating surface of the donut seal, and nowhere else. I wanted to avoid making a big mess. See figure 5.


I bolted everything back together and cleared the code, after driving for about 30 minutes, the “permanent” code cleared and everything was back to normal.


I wanted to share in case this happens to someone else with a low miles Tacoma. I got some good information from this forum, but not this particular issue, especially on something with less than 100k miles.

 

A p0420 & p0430 is NOT a "permanent code", not a hard fault.
Anyone can clear that code with a scanner or disconnecting the battery....

The pam will need to see the original concern that caused the light to come on 3 different drive cycles or maybe even longer before the light comes back on, so youre not out of the woods yet buddy....

BUT, nothing to lose by starting there first.....


Were you able to get a visual on the cat in front of the cat monitor sensor, the front single cat just after the gasket you replaced?
How did it look....

 

Thanks for the comprehensive report on your issue and, more importantly, the fact that you were able to resolve it in a manner everyone can follow.
Posts that describe an issue and ultimately fail to explain how it was resolved are not very helpful. Your solution and satisfactory resolution is much more helpful.
BTW, welcome to TW and thanks again for your post.

 

@slater Thanks for your input. I'm not sure what you mean about the code. It is an emissions issue so if I clear the code, it shows up as "permanent" in my scan after clearing it. After the repair, I cleared the code, drove around for awhile and the "permanent" code disappeared.
If I just cleared the code, it would still show up as permanent, and within a few minutes, the check engine light would come on too.

It's been a few days of normal driving and its still clear. It's run through enough cycles to be ready for NYS emissions.

As far as the cat inspection, I could only see the honeycomb from the back, looked fine. I gave the whole unit a shake, no rattling detected. There's a bend in the front that prevented me from seeing the inside material. (A borescope would work). I considered trying some methods of cleaning the inside, like pumping soapy water through it, but I decided to tackle one thing at a time.

@CT Yankee Thanks so much! I hope someone with this issue can benefit. I'm willing to bet an unscrupulous mechanic would want to change the whole catalytic converter (and donut seal) which would solve the problem, but would cost much much more.

 

If the cat is compromised / melted at all, its usually the very front.

Forget all the technical mumbo jumbo about the code in regards to permanent.

You cleared the code, its gone now....

The PCM needs to detect out of range cat monitor sensor numbers atleast under 3 different drive cycles generally speaking before it throws the code back on for a "inactive" cat converter......

Just cuz you made a repair, & the light hasn't come back on within the last week, doesnt mean you actually fixed anything.....

Thats all im trying to educate you on, about....

Im not trying to rain on your parade, I hope you in fact fixed it.....
On fords, Ive never seen an exhaust leak & ive repaired MANY severe ones, cause a p0420 or p0430 to be triggered & sounds like your leak was very minimal....