Code 0420 - S-10 Forum
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post #1 of 19 Old 04-29-2019, 04:32 PM Thread Starter
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Code 0420

Comes up as 'catalyst inefficient' or something. I really hope this doesn't mean I need a new cat, does it?

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post #2 of 19 Old 04-29-2019, 04:42 PM
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Re: Code 0420

Pretty much...

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post #3 of 19 Old 04-30-2019, 02:31 AM
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Re: Code 0420

Could also be caused by the post cat O2 sensor being defective. You need to read the outputs of the O2 sensors with a decent scanner capable of reading the voltages of each. No other way to check.
It it's not the post cat sensor, you are, as Rhotpursuit says, pretty much in need of a cat. You can drive it awhile as is, if there are no driveability issues. Eventually it will cause problems.
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post #4 of 19 Old 04-30-2019, 07:41 AM Thread Starter
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Re: Code 0420

02s are way cheaper than a new cat. I may try both for the **** of it. 177K miles, couldn't hurt to put new 02s in. I don't have any other scanner, beside the cheap harbor freight one.


Rock has up/downstream sensors from ultra-power for $45 shipped. I can't seem to find a matching set in amazon.
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post #5 of 19 Old 04-30-2019, 07:50 AM
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Re: Code 0420

Is the cat still the factory original? Or has it been replaced in the past?

Is it burning oil? Has it had head gasket issues, including coolant loss? Catalysts don't "just die." Something kills them. If you don't fix the underlying problem, you'll be feeding it new cats every year or less until you do fix the underlying problem.

As stated, it might be the downstream O2 sensor. That sensor can fail in a very specific way. If that's what has happened, it will be very obvious if you watch a graph of the "O2 sensor voltage" on the "bank 1 sensor 2." It's very rare for that problem to happen without also setting a code for the downstream O2 sensor. The P0420 by itself is almost always a catalyst problem, and an O2 sensor problem almost always trips other codes related to the O2 sensor itself.

Throwing new O2 sensors at a P0420 code without checking the wave forms from the O2 sensors is usually just a waste of money, but it's your choice.

Every machine is a smoke machine if you operate it wrong enough.
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post #6 of 19 Old 04-30-2019, 08:06 AM
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Re: Code 0420

At 177K the cat, if it's the original, is likely past it's operational lifespan or as stated above contaminated with something.

If you are even thinking about a bottle of catalytic converter cleaner, be sure to get it from a snake oil salesman on a covered wagon.
It's still the same formula it was in the 1860's. 2% water, 49% gullibility, and 49% ignorance.
There will always be somebody willing to take advantage of people looking for a simple cure.
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post #7 of 19 Old 04-30-2019, 08:55 AM Thread Starter
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Re: Code 0420

Quote:
Originally Posted by oldeerslayer View Post
If you are even thinking about a bottle of catalytic converter cleaner, be sure to get it from a snake oil salesman on a covered wagon.
It's still the same formula it was in the 1860's. 2% water, 49% gullibility, and 49% ignorance.
There will always be somebody willing to take advantage of people looking for a simple cure.



I've never even heard of such a product, and I'm sure as **** enough of a gear head to know something like that won't work anyway.


As far as I know, the entire exhaust is original. It doesn't burn any oil, no head gasket leaks. I've got 30K miles of oil analysis of clean oil.
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post #8 of 19 Old 04-30-2019, 12:47 PM
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Re: Code 0420

Quote:
I'm sure as **** enough of a gear head to know something like that won't work
But you don't own a scanner that can read O2's?
Costs under $25 for a BAFX bluetooth adapter and $9 for Torque Pro app for your phone.
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post #9 of 19 Old 04-30-2019, 02:01 PM Thread Starter
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Re: Code 0420

I've also been laid off for the past 2 months, broke my leg doing side work to try and get more cash, and pinching pennies every way I can. Which is why I REALLY hope it's not a $150+ cat.


I'm going tomorrow to sell some blood to help recoup the $250 I had to shell out for the womens valve body in the saturn.
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post #10 of 19 Old 04-30-2019, 07:29 PM
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Re: Code 0420

I'm with the "cats don't just die" statement. My '01 2.2L has nearly 260k on the original cat and O2 sensors. ****, even my old Tempo made it close to 200k on the original stuff when I sold it.




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post #11 of 19 Old 05-01-2019, 06:16 AM Thread Starter
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Re: Code 0420

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Originally Posted by manbearpig View Post
I'm with the "cats don't just die" statement. My '01 2.2L has nearly 260k on the original cat and O2 sensors. ****, even my old Tempo made it close to 200k on the original stuff when I sold it.



So you're thinking it's the O2 sensor also? Like I said, unless something immediately happened, it doesn't burn oil, and there's never been coolant in the oil. My oil change intervals can go up to 6-7K, and I don't think I've ever added oil. It leaks here and there, but nothing bad enough to add. Coolant has always been filled to the brim without touching it, and all my samples have been clean.


So unless something major JUST happened, the motor itself has been fine since I've owned it. Would it be worth changing both sensors, to keep them both new and in sync, or just the one?
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post #12 of 19 Old 05-01-2019, 07:19 AM
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Re: Code 0420

Older O2's tend to respond slower or "get tired". Just be sure to get good ones. I've always like Bosch. Good QC at a reasonable price.
Since price is an issue avoid the LAPS. They're usually promoting house brands that most time are cheap Chineseum at quality parts prices. That's how they are able to afford the brick building and property taxes. I usually get Rockauto parts in 2 or 3 days because they use FEDEX which is the fastest carrier.
There is a 5% discount code for forum members. Look it up in the vendors forum section.
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post #13 of 19 Old 05-01-2019, 08:14 AM Thread Starter
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Re: Code 0420

I always use rock, unless I need something right away. I can get 2 ultra powers for $45.
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post #14 of 19 Old 05-01-2019, 05:21 PM Thread Starter
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Re: Code 0420

I took it for a good ride today, no code. Maybe it was a one time fluke. If it comes up again, I'll order the o2 sensors.
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post #15 of 19 Old 05-01-2019, 07:02 PM
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Re: Code 0420

The cat in my 2002 tutu was damaged by a misfire. The spark plug anti- foul trick worked until it started to rattle. I bought a cat from Amazon for $110 that included bolts and gaskets https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
My 1992 has the original cat @ 357k
One of the instructors at a GM school said "Catalytic Converters never die of old age, they are always murdered."
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post #16 of 19 Old 05-01-2019, 08:47 PM
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Re: Code 0420

Quote:
Originally Posted by oldeerslayer View Post
Could also be caused by the post cat O2 sensor being defective. You need to read the outputs of the O2 sensors with a decent scanner capable of reading the voltages of each. No other way to check.
It it's not the post cat sensor, you are, as Rhotpursuit says, pretty much in need of a cat. You can drive it awhile as is, if there are no driveability issues. Eventually it will cause problems.
The only one I've ever seen that had a P0420 and a bad O2 sensor had a bad upstream sensor (very slow, but just under the threshold for setting a "slow" code). The upstream was so slow that the downstream had nearly the same waveform, tripping the P0420. I'm not sure exactly how a bad downstream O2 (with a good upstream one) could trip a P0420 without tripping another DTC that's related to the O2 sensor.

Other than the one time I've seen a bad upstream cause a P0420, every other P0420 I've seen needed a catalytic converter. I've probably averaged 2 to 3 per year over the past 25 years or so. That's around 1 every 18 months for the past few years when I've been semi-retired, and as high as one every month or two when I worked in busy shops and dealerships.

Quote:
Originally Posted by oldeerslayer View Post
At 177K the cat, if it's the original, is likely past it's operational lifespan or as stated above contaminated with something.

If you are even thinking about a bottle of catalytic converter cleaner, be sure to get it from a snake oil salesman on a covered wagon.
It's still the same formula it was in the 1860's. 2% water, 49% gullibility, and 49% ignorance.
There will always be somebody willing to take advantage of people looking for a simple cure.
I'm not going to recommend snake oil. However, I've seen some success with "cataclean" (against my recommendations) after I fixed the coolant leak issues that poisoned their catalytic converters, and both instances that I've observed successfully cleared the P0420 at least for a couple years. One of them ran for more than 5 years and never had another issue with the cat. That owner brought two bottles to me, "Cataclean" and one other product and said he understood that if it screwed up his injectors, fuel pump or anything else fuel related that I was going to charge him full rate, full labor for the fix. He said it wasn't a question of whether he was going to use the stuff, the only answer he wanted from me was which of the two products he had was he going to pour in the tank and which one was he going to return. I picked the "cataclean" as the least likely to be harmful.

The other one, I'm not sure what they used, but they came back almost 3 years later with the P0420 again, and I was starting to look up the paperwork for a warranty claim on the cat when I realized that I never changed it out. They said they used "some cleaner in the fuel tank" to "fix" it after I did the gasket job when it had the P0420 error. Whatever they used, it cleaned it up enough to work without the P0420 code for almost 3 years.

That stuff is firmly in the "can't hurt much, might help" category with me now. I wouldn't recommend it to anyone, but if you want to try, it's probably not going to hurt anything other than the cat, which is already going to need replacing if the "cleaner" doesn't work.

Quote:
Originally Posted by Hoosier Rick View Post
The cat in my 2002 tutu was damaged by a misfire. The spark plug anti- foul trick worked until it started to rattle. I bought a cat from Amazon for $110 that included bolts and gaskets https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
My 1992 has the original cat @ 357k
One of the instructors at a GM school said "Catalytic Converters never die of old age, they are always murdered."
I would recommend the OP spend a little money on the BAFX OBD-II adapter so they can do more diagnostics, and a spark plug anti-fouler. That's more likely to "work" as a temporary fix than a new O2 sensor. And having the diagnostic tool to check on things will help determine when the problem is back and bad enough to warrant a new cat.

And I completely agree about cats not dying of old age. They are always killed by something else.

Every machine is a smoke machine if you operate it wrong enough.
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post #17 of 19 Old 05-01-2019, 10:33 PM
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Re: Code 0420

This thread is TOTALLY disappointing! I was so hoping this was a 420 thread l,not a P0420 thread...I’m ready!

With that said I’ve had that code on 2.2 trucks,and it was the O2 sensor. I’ve had 2 cats fail,and neither put the check engine light on..just couldnt go over 55mph��

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I turned mine into an Oldsmobile, bitches love Oldsmobiles.
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post #18 of 19 Old 05-02-2019, 07:04 AM Thread Starter
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Re: Code 0420

since you mentioned misfire, I did have that misfire problem for just a second. I changed the coils, and the bolts felt like they were going into stripped plastic. One fell out while driving, the coil got loose, and made a misfire. But it was barely running for 5 complete minutes with the misfire before being towed and fixed. Could that have killed the cat in such a short time?


I did drive it for a while yesterday, and no code came up, everything felt normal.
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post #19 of 19 Old 05-18-2019, 10:29 PM
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Re: Code 0420

I'm attaching a technical Service Bulletin on this code. DTC P0420 could be because of a grounding issue.
Attached Files
File Type: pdf TSB 06-06-04-046.pdf (150.2 KB, 13 views)

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