CEL Code p0420

Wondering if anyone has experienced this code on a CEL before its showing catalysis below threshold wondering if I will need new catalytic converters or if the o2 sensors will need to be replaced.

 

It can be caused by a number of things. If you floor it and you get a flashing CEL and/or your RPM won't go past a certain point then it is likely the cat. But as I said, it can be caused by a number of things. Bad O2 sensors and cracked heads (which caused my cat to clog in my last pickup) to name a few.

 

I went thought his on my new (to me) 2012 Tacoma a couple of weeks ago. If you're getting the P420 code, it means your ECU at least THINKS your O2 sensors are working properly. If you have an O2 sensor that fails to read properly during the diagnostics the ECU runs...it will throw a code for an O2 sensor problem and will never even get to the Catalyst test.

On mine, for instance. I got a sensor code. Replaced the sensor. Still got the sensor code. Replaced the other sensor. That fixed the sensor code....but after 10 miles or so I got the P0420 code as it was finally able to check the catalyst system and the readings showed it was "past it".

Based on all my reading (a lot) the things that can cause that code are legion....but the most common in order are likely:

1. Catalytic Converter not working properly.
2. Exhaust Leak
3. Other engine issue (running rich for some reason...EGR, valve issue, etc.)

At this point...what I did...and what you need to do is check your taco to see if it is subject to a recall for catalytic converter replacement:

https://www.toyota.com/recall

When I entered my VIN there I found mine WAS and Toyota replaced my entire CAT assembly for free with brand new Toyota parts FOR FREE....and that fixed my code. I have about 400 miles on it since repair...and fingers crossed the CEL is off.

If you are not as lucky as I was....check for exhaust leaks. You can look online for various home brew remedies to restore your exsting cats. You can also buy new cats. I was leaning towards replacing mine with a Walker brand replacement assembly that looks to be totally bolt in and correct and costs in the $600 to $800 range rather than Toyota parts which I hear run a couple of grand.

Oh...I should point out...my truck had no other symptoms. It ran fine. Accelerated as it should. Idled good. All that. The only symptom was the P0420 code which I reset twice and it came back within 15 miles each time. If you have other symptoms...those would likely lead you a different direction.

Good luck!

Phil

 

Did you search the forum? There are several threads on this topic, mine included.

Mine was a leak where the cat connects to the Y pipe.

 

3 out of 4 times its the cat with a PO420. Easy way to test a cat as many shops do it this way.

TEMPERATURE DIFFERENTIAL TEST
The conversion process produces heat. So, exhaust gases entering the converter should be cooler than the gases exiting the converter. The temperature differential test measures the surface temperature at the inlet and outlet bushings of the converter. If conversion is taking place, then the outlet bushing reading should be higher than the inlet bushing reading. However, different pipe wall thicknesses and corrosion, along with different heat transfer rates may cause inaccurate results. So the EPA recommends that this test be used only to prove that a catalyst is good.

Make sure that the engine is fully warmed up and running and that the heater is off. Using a pyrometer or infrared thermometer, read and note the temperature of the pipe just ahead of the converter inlet at the weld ring. The weld ring is the point where the inlet pipe is welded to the converter body. Read and note the temperature at the weld ring of the outlet pipe. Calculate the difference between your readings. If the outlet reading is higher than the inlet reading, you can be assured that at least some conversion is taking place. On well-tuned, newer vehicles, the catalyst can be fully functional at only a 20°F difference. 

 

I had a P0420 and occasional P0430. Due to those I thought my cats were bad. A shop I went to said the same thing.

Decided before making a huge purchase to replace the gasket after the exhaust manifold cat. When I took it apart it was pretty well gone. Replaced both and zero issues. Don’t get caught up on having a bad cat just yet.

 

I call bs that the majority of the time it's the cat. I got almost 350k miles on mine. My p0420 code was fixed by replacing a gasket.