Got the OBD code P 0420 Catalytic Efficiency below threshold Bank 1 01/02 Bank 1

[werminghausen]

I got the code twice now.... every 4 weeks.
What do you suggest? Is there any standard procedure?
It could be all sorts of things like...
1) Exhaust leak anywhere before this sensor
2) Rear O2 sensor is faulty
3) Front sensor faulty
4) Bad catalytic converter


Best, Martin

 

[werminghausen]

It is a 1997 4Runner 3.4liter....

 

[jpeaslee]

Here are a few threads you might read through first. If you google "site:toyota-4runner.org/3rd-gen-t4rs/ whatevertyouwantotsearchfor", you can very easily search the forum and subforums for things, especially shorter search words. you can even use Boolean operators to help narrow your search.
1, 2, 3, 4 5

 

[CVELD77]

Mine is a 99 with the same code and i replaced the rear downstream o2 sensor and it fixed the problem. Make sure you get the proper o2 sensor for your emissions there was alot of options on the sensor and i also went with the Denso

 

[werminghausen]

Thanks,

I think I'll start with replacing the downstream O2 sensor. If the code comes on again... I'll dig further.

Martin

 

[JKC2638]

Most likely the cat conv. Not likely the sensors or exhaust leak. The way the code is triggered is when both sensors are reading the same. the rear sensor should read mostly flat around .2volts. when the rear sensor fluctuates up and down like the front it shows the converter is not cleaning the exhaust.
Have someone with a scan tool look at the readings so you don't waste money throwing parts at the code.

 

[jeremyc74]

Most likely the cat conv. Not likely the sensors or exhaust leak. The way the code is triggered is when both sensors are reading the same.

Replacing the rear sensor cures this for a lot of people, especially on CA emissions vehicles. I replaced mine at about 190k and haven't had a code since.

No way I'm spending that kind of money on a new converter for something with this many miles on it.

 

[werminghausen]

I crawled under the car today and saw that the last rear muffler tube (flanged to the muffler) was entirely disconnected...flange rusted off.
Could it be that the missing piece could could have thrown a code?

Maybe not...anyway I'll order this downstream o2 sensor and will replace the tube of course.

Martin

 

[werminghausen]

Thanks so much , very helpful reading...

Here are a few threads you might read through first. If you google "site:toyota-4runner.org/3rd-gen-t4rs/ whatevertyouwantotsearchfor", you can very easily search the forum and subforums for things, especially shorter search words. you can even use Boolean operators to help narrow your search.
1, 2, 3, 4 5

 

[TheDurk]

Most likely the cat conv. Not likely the sensors or exhaust leak. The way the code is triggered is when both sensors are reading the same. the rear sensor should read mostly flat around .2volts. when the rear sensor fluctuates up and down like the front it shows the converter is not cleaning the exhaust.
Have someone with a scan tool look at the readings so you don't waste money throwing parts at the code.

How can you say this? At the age of these trucks, failing sensors and exhaust leaks are common occurences. On my 1999, in March 2009 at 113k miles, I got a P0420. As there were no exhaust leaks and rear sensor was original, I swapped it for a new Denso and cured my P0420. The front had been replaced for a different code at 85k and I figured changing the rear sensor was good PM whether it was at fault or not.

That is, until October 2012, at 149k, the P0420 came back. I checked again for exhaust leaks and one of the bolts and the gasket at the joint between the two cats were rusted out and there was a strong leak, just not enough to be noisy. New gasket and bolts from NAPA for less than $10 and P0420 gone again and is still gone.

I assume you would have told me the cats were more likely the culprit on both those occasions.

Do you per chance work in a dealer service shop? Note: I wouldn't trust their diagnostic for a New York second. A dealer would probably have sold me two sets of cats. These factory cats are built like Sherman tanks and barring physical damage or an out-of-tune engine, they still have a lot of life in them. These cats don't die on their own; something has to kill them. You also don't want to replace them, without knowing why they died.

 

[JKC2638]

The last part of my post says look at the readings. That will tell you whats wrong. When the sensors don't function they get contaminated. Like you said the root cause should be fixed before replacing any of these parts. I should have said I have seen more cats bad. Working at a dealer we see more cats because a lot of time the customer has already tried replacing the sensors.
Bottom line I hate seeing people throw money at a guess. It's important to have a qualified person diag the concern. Dealer or private. A few dollars spent could save a lot of money and wasted time.
Just trying to help hear.

 

[TheDurk]

The last part of my post says look at the readings. That will tell you whats wrong. When the sensors don't function they get contaminated. Like you said the root cause should be fixed before replacing any of these parts. I should have said I have seen more cats bad. Working at a dealer we see more cats because a lot of time the customer has already tried replacing the sensors.
Bottom line I hate seeing people throw money at a guess. It's important to have a qualified person diag the concern. Dealer or private. A few dollars spent could save a lot of money and wasted time.
Just trying to help hear.

So...you should have said: "....not likely the sensors if you have already replaced the sensors." I fail to see how it is a waste of money to replace a rear sensor that is already end-of-life when it could turn out to be the quick fix that avoids having to pay a diagnostic fee that is more than the cost of the sensor. That's what I hate.

 

[JKC2638]

What I am trying to get across here is that doing a proper diagnosis will end up saving money and or time on the repair. How do you know a sensor is at the end of its life if you don't look at the readings. They could last 50,000 miles or 250,000 miles. There are many places that won't even charge a diag fee to look at check engine lights. Including some dealers. Just find someone to trust. I'm not trying to argue with you but i have been doing this for over 30 years. Everyone has an opinion. Take it for what its worth.

 

[jeremyc74]

Bottom line I hate seeing people throw money at a guess. It's important to have a qualified person diag the concern. Dealer or private. A few dollars spent could save a lot of money and wasted time.
Just trying to help hear.

It costs about $60 for the sensor, and almost anyone can do it themselves. You can't even get a qualified tech to plug into the car for less than that. Chances are at this mileage the sensor needs to be replaced anyway. It's a logical first step.

 

[TheDurk]

What I am trying to get across here is that doing a proper diagnosis will end up saving money and or time on the repair. How do you know a sensor is at the end of its life if you don't look at the readings. They could last 50,000 miles or 250,000 miles. There are many places that won't even charge a diag fee to look at check engine lights. Including some dealers. Just find someone to trust. I'm not trying to argue with you but i have been doing this for over 30 years. Everyone has an opinion. Take it for what its worth.

Well, I've been wrenching for over fifty years, and my day jobs were mainly in financial analysis. I am going to leave aside the dealer mistrust issue, generated by the many posters on here who were told by dealers they needed new cats and were able to resolve the problem in other, far cheaper ways.

The fact is the only free diagnosis you can get is a code scan, and that has already been done--it's a P0420. You are talking about a higher level diagnosis scan, and that is at least $100, more at dealers. Assuming you have ruled out exhaust leaks, it will only give you one of two results. Bad cats, or bad sensor. If you can change the rear sensor for less than the cost of the diagnosis, and it works, no more P0420, you have fixed the truck and saved the diagnosis fee. You are ahead.

If it does not, you can go ahead and change the cats, with or without a fancy diagnosis, and you are no worse off, as any dealer will install new sensors with new cats anyway, so how does the diagnosis save you money? Ah--only if the diagnosis is a bad sensor. As you said, if the cats are bad, odds are they contaminated the rear sensor anyway. (You said sensorS, but in your 30 years I doubt you saw a case where bad cats could contaminate a FRONT sensor.) But if that is the diagnosis, we fixed that, and saved the diagnosis fee.

I didn't KNOW my sensor with 110k was bad, but I knew the probability was high enough that it was bad or would go bad relatively soon to make spending the money to swap it a good investment rather than spend money on a diagnosis which fixes nothing, again, leaving aside the trust issue, which is real.

P.S. I passed NJ emissions yesterday, on my factory cats, five years after my first P0420.

 

[Rock_Rat]

Just a quick input on the thread. As an original owner with 300K plus I've replaced several O2 sensors due to the 0420 code but never my Cat's. If I get the code again, the first thing I'll replace without even testing is the rear sensor. If that doesn't fix it, then the front sensor. That's just based on experience and understanding how the sensors, the CATs and the ECM interface in open and closed loop.

As for a dealer diagnostic, I had one done when I had problems with my 0330 knock sensor code. I needed to see the wave form to eliminate the ECM from the troubleshooting. The cost was $100 and the end resuilt in my case was using NAPA knock sensors instead of OEM. I needed something specific from the diagnostics that I couldn't get mysef. I now have a good diagnostic report for my files. The technician was great. I followed up with him to let him know what the fix was. I mean two brand new sensors and harness with the same code was really puzzling.

In your case, [MENTION=114238]werminghausen[/MENTION] you already know the interface with the ECM the sensors and the cat so a diagnostics from the dealer would lead you to the same result as the FSM. Nothing gained. Like [MENTION=10169]TheDurk[/MENTION] said I agree that a $100 would be better spent on a rear sensor first. You can also try some seafoam to blow some carbon out the pipe. Personally a 0420 code isn't something I would run to the dealer with. They're not going to tell me anything I don't already know.

 

[werminghausen]

Thanks everyone for the great input, especially Durk and Rock Rat:hello: but also the others.
As I said I ordered a Denso rear sensor (makes sense for a 180K car) and I'll double check for a potential exhaust leak. I didn't look too closely so far because I thought I hear no unusual noise.
But you said a leaking exhaust doesn't necessarily cause a noise issue. So how do you know if a connection is leaking if not noise? Do you 'feel' a blow by by hand?

Martin

 

[Rock_Rat]

Thanks everyone for the great input, especially Durk and Rock Rat:hello: but also the others.
As I said I ordered a Denso rear sensor (makes sense for a 180K car) and I'll double check for a potential exhaust leak. I didn't look too closely so far because I thought I hear no unusual noise.
But you said a leaking exhaust doesn't necessarily cause a noise issue. So how do you know if a connection is leaking if not noise? Do you 'feel' a blow by by hand?

Martin

Put your rig up on jack stands when you get ready to run the seafoam through the PCV hose. First look for unusual "stains" along your pipes. If you don't see any then have a friend standing by with a rag to block off the exhaust once the engine begins to smoke. There's enough smoke in the exhaust system from the Seafoam that you will definitely see it leaking if you have any holes in your system. The noise, if leaking, will also be more pronounced.

Not a huge fan of Seafoam or anything too foreign in my engine so I would go with a 1/4 cup max. Might need a third person to help you out. Best to you. For all the old timers out there, no potatoes in the exhaust!!

 

[TheDurk]

^^^what he said. I also like to use a thin piece of paper I hold in an oven mitt, and put it up close to all the joints in the system. If you can find some, those carbonless copies on old-fashioned multi-page forms are ideal.