P0420 Permanent Code

Video only talks about cleaning the MAF sensor or replacing the oxygen sensor. So it's one of those "lets assume the sensors telling us the mixture is too lean are lying" deals.

It'll solve the problem if the trouble code was wrong because the sensors were lying. If the sensors were doing their jobs, the code was right, and the mixture is too lean, the video only helps to clean your wallet.

Bit fanciful of the video to say "how to fix ... in 2 minutes", when it gives you a choice of two things to do. Maybe you can clean a MAF sensor in 2 minutes if you've done it before. I'd love to see you swap an oxygen sensor in 2 minutes. But what I'd really love to see you do is decide which of those will solve the problem you have and then do the one you decided on, all in 2 minutes.

Again assuming that either one will solve the problem, which it only will if it was a false report because of that sensor.

Lastly, the video shows you at the end using a scan tool app they promote to clear the code, and then rescan right away "to make sure everything is fine".

The car's monitor that checks for P0171 issues requires warmup, a few minutes of idling, and several minutes of cruising-speed driving, and that test has to fail on two separate drives for the code to come back. Being sure everything is now fine is not a right-away proposition.

 

In OP's case its best to start at those two since he is already having catalytic issues and his MAF sensors were never cleaned in 10 years.

What you think of this video Mr. Chapman

 

Not going to boost their views by actually watching, but from the description/chapters seems to be more of the same.


They missed the possibility of a stuck open EGR valve. Might as well replace that too, it's a measly $268.

 

Ya might be a little exaggerated to assume these are wallet drainers. They are merely cheap maintenance. A bottle of maf cleaner is $6, an aftermarket o2 sensor is as low as $19, catalytic cleaner $8, adjusting spark-plugs is free, etc.

And they don't necessarily say to do them all. They're merely suggesting the most common issues from an error code and where people could start.

 

I did boost their views by actually watching, but I'd have to agree with that assessment.

Now that I've seen two videos from that same source, I can say I'm not a fan. The video production quality is extremely slick, but it is being used to dress up content that's little more than clickbait. It's like a lot of what comes out of the kind of internet content mills that have sprung up, where it has to seem just enough like it might be telling you something useful to keep you on the page while the ads play.

This one is longer than the first, so instead of giving you just two possible "methods to fix" a code (and no help determining which one your issue needs or whether it even is one of those two), this one gives you six possible causes and nine possible ways to "fix" them (and no help determining which of those your issue needs or whether it even is one of them).

It doesn't warn you that one of its "fixes" (an O₂ sensor spacer) is nothing but an attempt to defeat the car's detecting the problem. It suggests stuff like dunking the cat in dishsoap water. (I think I have read some possible promising results from pumping heated oxalic acid through a cat for a while with a heater and pump. But dunking in dishsoap?) It uses the same stock footage of a black-smoke-gushing car twice, to suggest that's how you can tell if you've got a bad cat, or if you've got bad injectors. And it mixes in "possible causes" that strain the imagination as to how they would cause a P0420.

After watching all that, I have to come back to the basics. If you have a P0420 code, about the best way to learn what that code is telling you, and how to troubleshoot it, and how to fix it once the troubleshooting tells you what's causing it, is to turn straight to the P0420 troubleshooting section in the repair manual.

Toyota Service Information and Where To Find It | PriusChat

It won't be a slick video with all the fancy graphics. It's just words and pictures on pages. But they are correct, and they'll help you identify and fix the problem with your car, and that's worth as much as a whole lot of bling.

 

That's basically the same thing. That will also clean the OP's wallet because #1, he has to pay for the repair-manual. #2, The repair manual will eventually tell him to start replacing parts such as the o2 sensors, catalytic converters, etc.

In the end, that's just how it is when it comes to diagnosing and pin-pointing a problem. One has to start at the most common issues of an error-code until they find the root-cause.

One will never know the exact issue off the bat. For example, p0420 could be from a dirty maf, bad cat-converter, faulty o2 sensor, vacuum-leak, etc. Another example is a misfire, it could be from a bad head-gasket, or a fouled spark-plug, faulty ignition coil, vacuum leaks, carbon build-up, faulty EGR, etc.

Yes it could be this or it could be that but in the end, the best way is to start with the most common and cheapest such as preventative-maintenance like cleanings, or cheaper aftermarket replacements that performs just as good as oem. Even if you take your vehicle to a dealer or an independent-mechanic, they're not gonna know the exact issue off the bat and will start replacing things until it fixes the issue. That's just how it is.

 

This is not quite accurate.

The repair manual distinguishes between a diagnostic test and parts replacement. The result of each diagnostic test will indicate whether a certain component is faulty, and only if it is confirmed to be at fault will replacement be recommended. Nothing that is in working order will need to be replaced, even if it is cheap. Sometimes that may result in more than one part being replaced, but there is no guesswork involved.

The parts-cannon method is the complete opposite—replacing a part is the diagnostic test. One guesses that some part is faulty, replaces it, and sees if it "helped". If not, raise the budget and repeat.

This is a sensible approach if one has no data about the inner working of the system and no access to any diagnostic tools, but can get expensive real fast once cleaning-and-praying phase is crossed. A common solution may work off the bat for people in the largest bin on a histogram, but how would one know what bin they're in beforehand?

 

But it's wearyingly common for people who won't look in the repair manual to think that's what they would find if they looked there, and then say that's why they won't.

The first three vehicles I bought repair manuals for, they were around $200 and were easily the best money I ever spent on those vehicles. Once you have the manual it never stops saving you money, and also saving you the uncertainty of having to figure things out by guesswork, or having to wonder if that's what the dealer or mechanic you're paying is doing.

These days, with the access being $20 or free depending on what libraries, etc., are near you ... $20 is a tenth of what was already a smart investment when it was $200. Free is even less than that.

Also, here on PriusChat, as often as not, if you come along and post about having such-and-such code, some other member will come along and drop PDF from the manual section for that code. With a little more initiative, you can often find some older thread about the same code where that already happened.

Then not only did you not have to pay for the manual, you didn't even have to find the table of contents. It doesn't cost you any more than any of the other advice you'll be offered, but may serve you better than some of it.

... which is exactly what one is not doing, if relying too much on content-mill videos that toss together a bunch of issues, including some not even related to the code, with no help to rule them in or out.

Let's go with that example. What makes you think so?

 

P0420 indicates a low catalyst system efficiency which is commonly caused by the exhaust-system or fuel-system. A dirty or faulty MAF does not report the correct amount of air-intake which leads to either too little or too much fuel being injected, which throws the air/fuel ratio off. Hence the lean/rich issues.

 

Not so. Where are you getting your information?

P0420 indicates that the oxygen-storage capacity (OSC) of the catalytic converter has fallen below the minimum acceptable level.

The car measures the OSC while driving, by occasionally forcing a lean mixture for a short period, which drives additional oxygen into the cat, where it gets stored, and then the car forces a rich mixture for a short period, and watches for how long it takes for the downstream O₂ concentration to drop. The longer that takes, the better the OSC.

The car does need to confirm that it's generating the lean mixture in the first part of the test and the rich mixture in the second part. If it tried to run the test during open-loop control before warmup, it would have to depend on the MAF sensor to try to get the mixture right. But it runs the test later, during closed-loop control, when it can just look at the A/F sensor reading and say "yup, got the right mixture".

That's why the repair manual does include the A/F and O₂ sensors among the possible problem areas for P0420 (along with, of course, the cat itself, and ways the exhaust gas could be going where it isn't expected, like exhaust leaks or EGR valve issues), but does not include the MAF sensor.