Throwing Code: PO420

Today I had to drive about 40 miles out to Suffolk to "rescue" my sister, who said she had a coolant leak. Got there to find out it was just that her AC had gone. So I turned around to head home. This was my truck's first extended interstate run, and he hit the 1000 mile mark on the rebuild- I was happy about that, until the check engine light came on about 3/4 of the way home. I got into the area, stopped at Advance and used their scanner- and it gave me the code PO420- Catalyst System Efficiency Below Threshold (Bank 1).
This would explain why sometimes I feel like the truck loses a bit of power/starts acting sluggy. It doesn't happen often, though. What I'm gathering from this is that one of my O2 sensors is damaged or has failed, or the cat is clogged. Does anyone know of something else that it might be? I wanna start with the cheap things first so that I don't end up throwing a lot of money at something that doesn't need replacing...
This definitely happened at a bad time though. Because my truck is the only reliable vehicle we have right now- Dad's van is broken down, my sister's car has a badly slipping clutch, and the Honda is totaled. I have to take him to work, but I'm not sure I should be driving the truck if it's throwing codes.

 

I'm fighting the same code. My gas mileage is the same, power same, no signs at all. First thing is check for exhaust leaks, then test O2 sensors as best you can with a multimeter. Testing the cat...haven't figured that out yet.

 

My truck is throwing that too...anyone on here disable the o2 sensors and get rid of the code?

 

I would start with checking for exhaust leaks first, then try O2 sensors next if needed. Hopefully it's not the cats!

As far as drive ability and it being dependable, I don't think you have to worry. I drive on mine for a couple months before I could change the sensors And get new cats. Plus I've had many many cars that have these codes and driving on this code hasn't caused any issues other than acting slightly sluggish or loss of a little power, or even bad gas mileage.

 

How often is it really the O2 sensors? Don't they throw a different code?

 

Try resetting the code with the obd2 scanner, see if the code reappears after driving. sometimes it's a false code and other times you need to replace a sensor.

 

I did this- thought about it after I left Advance. Went to my buddy's house and cleared it with his scanner. It hasn't showed up again yet, and I've driven probably 40-50 miles since I did that. (Had to pick dad up from work.) I've heard of this happening before- dad said this has happened to him a couple times, and he will clear the code and it NEVER shows back up. Hopefully, this is one of those times.
My gas mileage isn't suffering at all, but sometimes I notice a slight lack of power/acceleration. I'll let y'all know if anything else comes up.

 

my 02 2.7l was throwing p0300 and now i'm suffering with this code. random misfiring. i replaced 2 of the 02 sensors, new set of plugs and coils.
clean and replace air filter, still don't help. any good suggestions or advices?
code P0420, 90% of the time is 02 sensor.

 

P0300, random misfire... Check coils, wires, and plugs for damage, arcing or blowby on the plugs. Spray brake clean at the intake gasket and see if it stumbles indicating leaking gasket. Spray a little, don't saturate or a little will seep in and cause a misfire and you'll think it's bad when it's not. Take apart your air box, and check the MAF to see if its clogged or dirty. Perform a fuel gravity check to see if there's too much water (too dense) and this is causing random misfires. If you had a single coil or plug issue you'd have a specific code, p0301, p0302.... Etc. maybe perform a fuel system cleaning, could be carbon as well. Think of things that would cause your car to skip- fuel, air, etc.

P0420 catalyst issue. Can you remove your cat and shake it? If you hear loose stuff inside then it's breaking apart and needs to be changed. Most likely, it's NOT your sensors as they usually have their own codes. I heard someone used "cataclean" to put in their engine and clean out the cat and it worked, but I've never used it. This code 95% of the time means new cat is needed. You can also check your fuel gravity with a test kit to be sure your fuel isn't causing issues and make sure you have NO exhaust leaks. Pulling in regular air can cause the cat to burn too hot and become damaged. If you look around online you may find inexpensive bolt on catalysts that will work just fine and same some real cash. Good luck to you!

 

On Neegdogdig's PO300 Code- I would definitely check the Mass Airflow, because when I first got my truck running, we ran around and replaced/checked everything but it- and the truck stumped us, because it was still running terribly. Realized we hadn't checked it, and when we pulled it, the little wire looked like it had been dropped in the dirt. Sprayed it with some MAF cleaner (you don't want to use anything else because the wire is fragile and other chemicals can mess it up) and the truck was good to go- cleared up the majority of the issues we were having at that time.
On my PO420 Code- My dad said that oftentimes when you get the PO420 reading, the O2 sensors are really just doing their job. He's heard of people replacing them, only for the light to come right back on, because they were truly reporting the correct level of oxygen passing through. Which would mean the cat is acting funny, or something else along the line.
I'm going to have to drive on mine for now, and hope that the light doesn't come back on. Hopefully it never happens again, but with my luck, it will. This has also taught me a valuable lesson though- I can't keep living like I am, "paycheck to paycheck" and not saving anything, because what if next time, the problem I'm having is one that makes my truck undriveable? I wouldn't have the money to fix it. This kinda got me to realize that I've gotta start saving for rainy days, and maybe get another job.

 

For the P0300 I would buy some electric parts cleaner from autozone, take off the MAF and spray the little wire on the side with the cleaner. Let it dry then put back on. Also clear the codes, hopefully that will take care of that P0300 code.

 

Mine turned out to be the cat but I knew it was bad, unbolt the cat and see if it's hollowed out or any holes in the honeycomb otherwise it's probably good.

 

ive gotten the 0420 code a couple of times...i just clear it and forget about it. really nothing to worry about

 

When the state has emissions testing, like mine, its definitely something to worry about.

 

The PO420 code hasn't come back up yet, and I've put about 150 miles on the truck since I cleared it. so hopefully it will stay gone!
And when we had the scanner hooked up to clear it, I read all the info it was pulling from the truck. The Oxygen levels passing the sensors were within spec. I guess it just got too high or too low once and it was enough to trip the light.

 

It has happened twice since I have owned the truck. If it happened to appear in the month I have to to a test I'll clear it and go test it. Done

 

CEL came back on when I was on the interstate taking my dad home from work... I guess tomorrow I'll hook up to a scanner again and make sure it's the same code being thrown before I start doing anything.
Not looking forward to this... gonna be a couple weeks of busting my ass to save up to be able to do anything about it.

 

Cleared mine and it's back also...guess 206k on the stock cat ain't too bad...

 

For the P0420, clean your MAF sensor, it's easy and cheap. Especially do it if you're running an oiled air filter. Ask me how I know.

 

The cat on my Taco is stock- so it's got 145k on it. The cat could very well be clogged, because I know that when this thing was parked before I got my hands on it, it was hardly running and running rough, lots of trash and buildup. Then it sat for several years. It wouldn't surprise me if the cat is clogged or something, since I know how it ran. I gathered info on how it had run before being parked by the condition of everything before I did the rebuild.

Cleaned the MAF 3 days ago, when the code showed up the first time.