The dreaded P0420
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
The dreaded P0420 So I just bought this car, 02 Trans Am Ws6, 57k miles... 3 weeks later... P0420 
Makes me wonder if the dealership didn't just clear the code to sell it to me. (established company in my area)
I am going to start troubleshooting this to make sure it's not the converter, But from my reading about the extended warranty GM offered due to Cat failures on this car, I am not really hopeful.
I looked at some stock pics of the cat setup, and it looks really really tight to have a replacement universal converter welded onto the existing pipe/flange. Not sure it can even be done?
I do, however, notice that on Summit, flowmaster
carries two stock replacements with flanges that run about 450 for both. *sigh*
I do remember hearing a high pitched "rattle" coming from under the car when my windows were down and I accelerated next to something, so the sound echoed back. Maybe the cat material has started to break up? I was leaning towards a heat shield before the code popped up.
No loss of power. Although, the exhaust does have a funny sound to it when you give it small revs (2000-2500). I can't even describe it. When the RPM's come down, it sounds similar to a horse blowing air through its nose?? LOLOL that's the closest I can relate it to! We call it a Nicker or a snort.
It looks like I need to take it to an exhaust shop and have it checked for leaks and have the cats looked at. I know a good shop in town that should be able to give me some good info.
I also have a buddy trying to acquire a scan tool from his work so I can check the 02 sensors.
We shall see! Anyone else get this awesome code lately?
Makes me wonder if the dealership didn't just clear the code to sell it to me. (established company in my area)
I am going to start troubleshooting this to make sure it's not the converter, But from my reading about the extended warranty GM offered due to Cat failures on this car, I am not really hopeful.
I looked at some stock pics of the cat setup, and it looks really really tight to have a replacement universal converter welded onto the existing pipe/flange. Not sure it can even be done?
I do, however, notice that on Summit, flowmaster
carries two stock replacements with flanges that run about 450 for both. *sigh*I do remember hearing a high pitched "rattle" coming from under the car when my windows were down and I accelerated next to something, so the sound echoed back. Maybe the cat material has started to break up? I was leaning towards a heat shield before the code popped up.
No loss of power. Although, the exhaust does have a funny sound to it when you give it small revs (2000-2500). I can't even describe it. When the RPM's come down, it sounds similar to a horse blowing air through its nose?? LOLOL that's the closest I can relate it to! We call it a Nicker or a snort.
It looks like I need to take it to an exhaust shop and have it checked for leaks and have the cats looked at. I know a good shop in town that should be able to give me some good info.
I also have a buddy trying to acquire a scan tool from his work so I can check the 02 sensors.
We shall see! Anyone else get this awesome code lately?
Last edited by JacksonJ; Jul 21, 2015 at 06:56 PM. Reason: Typo
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
Now that I think about it... I did just install an SLP lid... although I fail to see how this would cause an issue? Sure it flows a little better... but it's not a significant change that would require a tune.
TECH Fanatic
Joined: Jun 2011
Posts: 1,746
Likes: 238
From: dayton, ohio
Magnaflow makes a universal cat converter that fits our cars. Check out Advance Auto to find the exact price. I had to put one on my 1998 v6 Firebird last year and I have no complaints with it.
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
It seems like there would be no room to weld in a replacement? Unless someone has done it?
Trending Topics
Joined: Nov 2001
Posts: 34,629
Likes: 2,550
From: Schiller Park, ILL Member: #317
P0420/P0430 is quite common on the '00+ cars, hence the warranty extension you mentioned above.
I got this code as well, on my '02 car, many years ago. I just disabled the code and never worried about it again, but we don't have a sniffer test here so I didn't care if the cats were doing their job or not. I had no driveability/MPG issues, no power loss, and also no odd rattles or exhaust sounds. Typically the cats don't break apart with these codes, the coatings just wear off the substrate negating their ability to "scrub" the exhaust, but sometimes they do so if you're hearing odd noises then perhaps this is the case for you.
If you don't have a sniffer test, you can just remove them and disable the codes.
I got this code as well, on my '02 car, many years ago. I just disabled the code and never worried about it again, but we don't have a sniffer test here so I didn't care if the cats were doing their job or not. I had no driveability/MPG issues, no power loss, and also no odd rattles or exhaust sounds. Typically the cats don't break apart with these codes, the coatings just wear off the substrate negating their ability to "scrub" the exhaust, but sometimes they do so if you're hearing odd noises then perhaps this is the case for you.
If you don't have a sniffer test, you can just remove them and disable the codes.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
P0420/P0430 is quite common on the '00+ cars, hence the warranty extension you mentioned above.
I got this code as well, on my '02 car, many years ago. I just disabled the code and never worried about it again, but we don't have a sniffer test here so I didn't care if the cats were doing their job or not. I had no driveability/MPG issues, no power loss, and also no odd rattles or exhaust sounds. Typically the cats don't break apart with these codes, the coatings just wear off the substrate negating their ability to "scrub" the exhaust, but sometimes they do so if you're hearing odd noises then perhaps this is the case for you.
If you don't have a sniffer test, you can just remove them and disable the codes.
I got this code as well, on my '02 car, many years ago. I just disabled the code and never worried about it again, but we don't have a sniffer test here so I didn't care if the cats were doing their job or not. I had no driveability/MPG issues, no power loss, and also no odd rattles or exhaust sounds. Typically the cats don't break apart with these codes, the coatings just wear off the substrate negating their ability to "scrub" the exhaust, but sometimes they do so if you're hearing odd noises then perhaps this is the case for you.
If you don't have a sniffer test, you can just remove them and disable the codes.
Texas does not sniff... but some inspection shops are known to visually check for the presence of converters...
A friend and work is pushing me to use this opportunity to redo my entire exhaust from LT's to Cat Back LOL
I will update when I know something more...
Joined: Nov 2001
Posts: 34,629
Likes: 2,550
From: Schiller Park, ILL Member: #317
I could be crazy about the noises I hear. I am still getting used to all the different sounds the car makes. I will run up to a muffler shop when I can to see if there is a physical issue with the cat.
Texas does not sniff... but some inspection shops are known to visually check for the presence of converters...
A friend and work is pushing me to use this opportunity to redo my entire exhaust from LT's to Cat Back LOL
I will update when I know something more...
Texas does not sniff... but some inspection shops are known to visually check for the presence of converters...
A friend and work is pushing me to use this opportunity to redo my entire exhaust from LT's to Cat Back LOL
I will update when I know something more...
P0420/P0430 don't directly indicate a clog or broken converter material (there is no code to indicate such), they only indicate a reduced oxygen storage capacity (meaning higher tail pipe emissions, which is what happens when the coatings wear off the substrate - this is the most common problem for these cats.) If you were to remove the cats completely you would get these same codes (unless you tuned them out), as these codes are not any indicator of flow.
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
I just don't know when that day is happening. I am not totally worried about putting a cat on it to get by for now, I would go with the cheapest EBAY I can find.
I am still really thinking this may be related to an exhaust leak. I just haven't had the time yet to diagnose it fully. As we get older, between work and a growing family, it becomes harder and harder to find some dedicated time to work on your hobby.
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
If the cat isn't the source of the sound you're hearing, and you have no other issues with power/driveability/MPG, and you don't have a sniffer test to pass, then you can just leave it alone and get the code tuned out (assuming you have an OBD scan test, or just don't want to look at the SES light forever.)
P0420/P0430 don't directly indicate a clog or broken converter material (there is no code to indicate such), they only indicate a reduced oxygen storage capacity (meaning higher tail pipe emissions, which is what happens when the coatings wear off the substrate - this is the most common problem for these cats.) If you were to remove the cats completely you would get these same codes (unless you tuned them out), as these codes are not any indicator of flow.
P0420/P0430 don't directly indicate a clog or broken converter material (there is no code to indicate such), they only indicate a reduced oxygen storage capacity (meaning higher tail pipe emissions, which is what happens when the coatings wear off the substrate - this is the most common problem for these cats.) If you were to remove the cats completely you would get these same codes (unless you tuned them out), as these codes are not any indicator of flow.
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
Finally made my way to an exhaust shop today.
There WAS a decent leak at the rear flange for the driver side converter. We have sealed that up for now. I am going to wait and see if my code comes back.
The tech did mention that the DS cat felt a lot hotter than the PS. I am going to hit it with my thermometer when I get a chance to verify.
Also... the rattling noise I have been hearing that led me to believe I had a bad cat could be the o2 sensor sleeve at the top of the sensor. We banged on the y-pipe and this is what seems to be making the noise. I am researching a few threads to see if crimping or high temp RTV is the best option to try.
Either way... I am stuck with a personal decision to spend money fixing the stock cats (if they are indeed bad) that I will ditch in the future. Or biting the bullet and purchasing the full header back exhaust that I planned on in the future.
450 for magnaflow direct replacement cats, or 1300 and get the whole thing over with.
I know some have mentioned going cat-less... Just don't think I can go that route.
Decisions... decisions...
There WAS a decent leak at the rear flange for the driver side converter. We have sealed that up for now. I am going to wait and see if my code comes back.
The tech did mention that the DS cat felt a lot hotter than the PS. I am going to hit it with my thermometer when I get a chance to verify.
Also... the rattling noise I have been hearing that led me to believe I had a bad cat could be the o2 sensor sleeve at the top of the sensor. We banged on the y-pipe and this is what seems to be making the noise. I am researching a few threads to see if crimping or high temp RTV is the best option to try.
Either way... I am stuck with a personal decision to spend money fixing the stock cats (if they are indeed bad) that I will ditch in the future. Or biting the bullet and purchasing the full header back exhaust that I planned on in the future.
450 for magnaflow direct replacement cats, or 1300 and get the whole thing over with.
I know some have mentioned going cat-less... Just don't think I can go that route.
Decisions... decisions...
For what it is worth, I had a P0430 code recently, I did my research to really understand the code and how to read the code reader voltages and graphs.
The values on the passenger side, bank2, O2s looked different on the graph compared to the drivers side, bank1, values and graph. At that point I decided to change both bank2 O2 sensors because they were old and much cheaper than an OEM cat. I purchased Denso O2 sensors from rockauto, $25 ea.
It corrected the P0430 and has been out for over two months now.
Here is a write up I did back in May...
https://ls1tech.com/forums/generatio...430-codes.html
The values on the passenger side, bank2, O2s looked different on the graph compared to the drivers side, bank1, values and graph. At that point I decided to change both bank2 O2 sensors because they were old and much cheaper than an OEM cat. I purchased Denso O2 sensors from rockauto, $25 ea.
It corrected the P0430 and has been out for over two months now.
Here is a write up I did back in May...
https://ls1tech.com/forums/generatio...430-codes.html
Thread Starter
Staging Lane
Joined: Jul 2015
Posts: 67
Likes: 0
From: Kilgore, TX
For what it is worth, I had a P0430 code recently, I did my research to really understand the code and how to read the code reader voltages and graphs.
The values on the passenger side, bank2, O2s looked different on the graph compared to the drivers side, bank1, values and graph. At that point I decided to change both bank2 O2 sensors because they were old and much cheaper than an OEM cat. I purchased Denso O2 sensors from rockauto, $25 ea.
It corrected the P0430 and has been out for over two months now.
Here is a write up I did back in May...
https://ls1tech.com/forums/generatio...430-codes.html
The values on the passenger side, bank2, O2s looked different on the graph compared to the drivers side, bank1, values and graph. At that point I decided to change both bank2 O2 sensors because they were old and much cheaper than an OEM cat. I purchased Denso O2 sensors from rockauto, $25 ea.
It corrected the P0430 and has been out for over two months now.
Here is a write up I did back in May...
https://ls1tech.com/forums/generatio...430-codes.html
Found out yesterday that my Mother in Laws new boyfriend is a master tech at a local GM dealer. He is SUPPOSED to stop by sometime soon and hook up a good scan tool and get some live data going.
I need to invest in my own, I dislike relying on others.