Trouble code P0420

Hi, I'm new on Tacoma World,

I own a 2003 Tacoma, Double cab, 3.4L, 4wd and an my check engine light cam on last weekend but the truc runs perfectly...

the code is P0420

"Repair information" P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Since the Cat and o2 sensors are very expensive I wouldn't want to change the part for nothing.

Did any body had this code and if so, what did you do to fix it!!??

thank you

 

I have the same code and I'm in the same boat your in. I have heard that it is a O2 sensor and a fuel/air mixture sensor. I have heard that you can buy a generic O2 sensor and just wire it in but sense it is also supposed to be a fuel/air mixture sensor I don't know if you can.

 

the cat and the o2 sensors would definitly be where to start, if you decide to replace ur o2 sensors you should do both at the same time. the prices at rockauto.com arent to pricey and you get a TW member discount IIRC. get a OEM replacement (denso,bosch). or if ya want you could buy a URD simulator it is meant to turn off the CEL when you get a P0420 code, although its more meant for people who run no cat or a high flow cat.

 

Hi!!

I've been reading A LOT on this P0420 problem and found out a few good thing you might like to know!!!

I lot of people have the same problem that we do, some changed everything related to emission system. Cats, o2 sensors, MAF, MAP, Temperature Sensor and still had the light coming on!!

On thing that not a lot a people think of checking is the Ethanol rating in the gasoline they use!! Toyota tacoma are set to use Gas with less then 10% ethanol... So what i did is I empty my tank and filled it back with ethanol Free Gasoline, unplug the battery to erase the codes and Guess what, no more light...

The problem with ethanol is that it doesn't burn like regular gas at all and our O2 sensors do not reconised the exhaust gas so your check engine light turn on!!!

I was using Gasoline that had 12% Ethanol and didn't know it!!

Try that and let me know what happens

Thanks

 

I had this code and it turned out to be a leak in the exhaust system, I just had to tighten the joint between the cat and the back of the exhaust. That's the first I've heard of ethanol causing the code, unfortunately many people don't have the luxury of choosing non-ethanol gas.

 

I think the gas idea may be along the right track. I used to buy my gas from a station that always had the cheapest gas which I'm guessing is probably because they use more ethanol in the gas.

My light would come on and I'd get it turned off then it would come on and I'd turn it off. So I seafoamed it and started running gas from a different station with "supposable" better quality gas and my light hasn't come on since. Knock on wood.

 

I have the same problem and i think i know the fix. Our 1st gens. i bellieve have 2 cats. one at the headers and one down the pipe a little bit. The code is a o2 code but you will never know which cat and o2 is causing it. I was told that you can cut both cats out and put one longer one in its place, then wire up one new o2 censor. any thoughts?

 

It's almost always the sensors. Do em both at the same time and get denso oem styles. Bosch will not work correctly, I found that out the hard way and still have one laying around somewhere. I've never replaced the front o2 sensor but the rear one is really easy *if* the old sensor isn't rusted into the bung.

 

i have the same code, but i also dont have my second cat and my URD simulator should be here by friday so that should fix it. it could also be a leak, for the longest time now i have heard a "puffing" noise on curbs, walls or any obstruction when i pass but can not for the life of me find it. i have checked, check, re checked, brought it to a muffler shop and still cant find the leak...its driving me nuts, it seems i only hear it when im hitting the gas so maybe thats why i cant find it when i look when its idling....

 

Only factory o2 sensors for me found out the hard way,(don't buy from vato zone ever!) denso should be what you want for sensors.

 

run some seafoam through the brake booster. i bet you find it then

 

i did that but i didnt think of looking for the leak and i did it myself, ill get a buddy to help me and norrow down next time i get some time to mess with it

 

Finally the problem was only an exhaust leak. The flange gasket between the second Cat and the extension, right before the second O2 sensor was finish. I replaced it, erase the codes and voila!! done... the check engine light is off since 2 month now...

The reason the check engine light goes on with P0420 code is because when you are driving at a constant speed, the flow in exhaust creates a vacuum and pull fresh air from exterior by the hole and falls the o2 sensors reading...

Verify leaks by blocking muffler and check for very small leaks, specially near o2 sensors!!

 

Well went to AutoZone and found out I have a code (po420) he said I have possible bad gas or a hole in my cat! Recommended fuel injector cleaner and a octane booster? I m thinking gas as I just filled up 50 miles ago from almost empty....

 

if you have 130,000 mile or more and it's the OEM sensor, it's likely the sensor itself that crapped out

they do wear out

 

I'll look into it lol I have 230k lol how would you tell.if OEM or not clipped wires?

 

Hello 1st Gen lovers,
Wanted to pass on what work for me in fixing my P0420 CEL.
2004 TRD with 165k on the clock.
Truck runs great and was getting slightly better fuel mileage with the CEL on.

Replaced upstream sensor, no change.
Replaced downstream sensor, no change.
Took it to the garage, they changed the mass air sensor in the intake. Worked for a week.
Took it back to the garage they couldn't find anything and suggested new CATs.
Made a shield for the downstream sensor, trying to imitate the spacer other people use to fool the sensor. no change
Let the truck sit over night. Had a friend plugged the exhaust outlet with his hand, started the truck and found 2 leaks. Since the truck was cold the leaks were easy to find since they dripped water (condensation). One leak was between the upstream and downstream sensor. Used some exhaust putty to plug leaks. Problem solved!

Thank you davestaco for the suggestion of looking for leaks, wish i would've tried that first..


UPDATE,

After a couple of months the Damn P0420 code came back. Found another pin hole in the exhaust between the 2 cats. patched it and code still came back. Truck was hesitating at full throttle, and through a misfire code. Check the spark plugs, all the electrodes were down to little points (ashamed I let them get that bad). Replaced spark plugs and the p0420 hasn't returned. And it runs great. Fingers crossed...

 

It's the upstream correct

 

It's the upstream. It's the more expensive O2 sensor and they are connector key specific.

I remember by looking at the connector notches. 1-2-3.

The downstream has a different combination and is dirt cheap.

 

@uaflyer
Welcome aboard new member
You might want to check the posts date stamp. 8 month old post.
And the upstream is an Air/Fuel sensor for that year Taco.