P0420 Code

I've owned my 01 Tacoma 2WD for over two and a year's. It's been a great and reliable vehicle and I've never had any problems until just lately. A couple months ago I pressure washed the engine and afterward, as expected, it ran a little rough. In the past a few miles down the road and it's smooth running again. But not that time. It got worse and I found myself stranded in a parking lot and couldn't get started again. I called for help and when tools came we started with checking spark plugs and found ALL four with electrodes burned down past the ceramic. (I saved them for those who wouldn't believe it. ) l never checked them because the engine always ran so smooth. With new plugs it was smooth rolling again. Except for countless codes it seemed to run perfect. I kept a close watch and was relieved when the codes went away one by one. Except for P0420. Then I got a letter from Califrnia DMV telling me it's time to renew my registration and that I'll need a smog certificate. The odometer just turned 300,000. But according to the seller the catalytic converter was less than a year old. The catalytic converter and related sensors are expensive and I don't want to replace them unless I need to. I read about how cheap gas with ethanol can trigger a P0420 Code on Toyota's. So with high hopes I'm ready to try a method that May allow my truck remove the code itself. First. I filled the tank with good quality premium gas with no ethanol and I'll also add a double issue of octane booster. I'm also told there's a series of driving speeds and the amount of time to be driven at those speeds. I had them written down but lost the notes. Can anybody tell me again what those speeds and durations are?

 

I have same code on mine
210k miles

My smog will be next year

I plan to replace the two 02 sensors. As on this forum after lots of reading pretty sure that’s the culprit

I got under truck yesterday and on my 4 cyl doublecab both sensors look easily accessible

 

i would start by replacing the gaskets on the o2 sensors then get a cataclean additive to unclog the cat and then just run it as normal for the readiness monitor

 

I got this code on my '04 right after filling up at an 'questionable' gas station on the way to a trail I was doing that day. About a mile into the trail, the CEL came on...pulled the code and got P0420. Cleared it on the trail and it came back almost immediately. A few days later, after I burned through that tank of gas I reset the code again and filled up at my usual gas station and added a fuel system cleaner (Lucas brand, if I recall). The code never came back and still hasn't; this was about 6 months/10k miles ago. My code reader shows no pending codes either.

I chalked mine up to bad gas but obviously there are other, more serious conditions that can trigger this code; the catalytic converter going bad being one of them. Running too lean or too rich can wreak havoc on your cats and that may have happened back when you were throwing all those codes that you mentioned before.

 

Mine has been on and off for a year

When I reset it sometimes it comes back within 500 miles

Sometimes it comes back after 8500 miles

All I know is it’s there .... and I need to fix before smog nazi early next year

 

Do you have a code reader? I'd be interested to see if it pops up as a pending code on the reader since it comes back intermittently.

 

Yes Neighbor I do

I am not sure how to read pending code

But when it turns off by itself if I check it there is no stored code

Then it comes back and when I check it it’s always the same one

Right now it’s been in for 1 month
Tired of clearing it

Don’t have tools to do the o2 sensor

 

The P0420 is a catalytic convertor efficency code. If you have a code reader do it have a "Smog Readiness" feature? If so keep checking to see if she is smog ready. I have a smog guy that opens at 7 AM and there are many times that when I have a P0420 and as soon as it is smog ready I drop it off at his place, even if it is midnight. I am the first guy there in the AM and I get the smog done. This way I have 2 years to figure out what exactly the problem is. If she is your daily driver and you cant do what I do you are just going to have to drive and check and drive and check then go to the first smog shop you see.

a small gasket leak in the exhaust system can cause this.

there is also a gadget that plugs into the rear O2 sensor lead that fools the PCM insto thinking that the cat is good... $100 ish if I remember... it is illegal and if your smog guy sees it under the passenger seat you are done.

 

So you are saying p0420 means I need a new cat and not new 02sensors ?

 

P0420 means the sensors are working and the cat has failed.

The upstream sensor is for fuel trim, the down stream is to monitor the cat. If the downstream pattern switches too fast and matches the upstream it triggers p0420.

If the sensors have failed you'd receive other codes.

 

Thank you

Didn’t realize that. For 6 months have been thinking I need new 02 sensors . Seems like I need a new cat


Guess I will see if it will smog with cleared codes and if it doesn’t , have to get a new cat


Appreciate the help

 

pretty sure that is incorrect. I replaced my front o2 sensor and front CAT, and still had a P0420. When i finally replaced my rear o2 sensor, it went away.

 

You need to monitor the sensors to diagnose it correctly. I've changed hundreds of Cats and rarely change the o2 sensors. The only times I ever see issues is with aftermarket cats.

 

Yea, I used a scanner, watched the o2 signal, even though my rear o2 sensor was showing data up and down it was way too erratic. Once I installed the new rear o2 sensor the signal got much more stable and the P0420 went away. The cat system is now "Ready".

 

If you wipe the code right before you go smog it, they will tell you that your ECU is not ready. I tried that. You have to put 40-50 miles on your truck after clearing the ECU for the ECU to be able to be read by the smog place. Just pray it's a good day and you CEL doesn't pop on before you drive up to get it smoged.

 

That’s what I had read here
Thus I was getting gonna replace sensors

After this thread figured I now need cat instead of sensor

So confused ‍♀️

 

Thanks

I have till December

Will clear and drive 50 miles see if I can make it

 

I've had this code for 3 years now I just clear it when it comes up. I passed smog when I had it just cleared and put some miles on the truck before heading in.

 

How many miles do you drive post clearing code and before smog ?

There has beeen times where mine has come back in 100 miles

And other times it hasn’t come back in 5,000 miles


I guess I can take a chance and clear + drive and attempt to smog

 

I can't remember how many miles. Like yours it'll throw the code 3 times in one day and then not throw it for the next 6 months. Just clear it put as many miles as you can and get the truck warmed up before going in.