DTC code and exhaust help - P0420
Thread Starter
On The Tree
Joined: Apr 2007
Posts: 165
Likes: 0
From: Bloomington, MN
DTC code and exhaust help - P0420 I know this has probably been asked a million times (and yes I read through the old threads) but I have some new questions I didnt see asked.
Just bought a 2004 CTS-V with 83k on it. Been driving it for a couple days and the check engine light came on. Seems to run fine, but it is giving me a P0420 code for bank 1 cat efficiency low.
Now the questions, how do i know if its the cat or the sensor(s)? How long do stock cats last on a stock car? Is there a way to test the 02 sensors or is it just a guessing game?
Last question, has anyone ever used these or heard any reviews on them?
http://www.mandrelexhaustsystems.com...EXHAUST/Detail
Theyre less than half the cost of the stockers from gmpartsdirect.
Are these something I can do in my garage without a lift? Im used to trucks where I can lay underneath easily.
Thanks
Just bought a 2004 CTS-V with 83k on it. Been driving it for a couple days and the check engine light came on. Seems to run fine, but it is giving me a P0420 code for bank 1 cat efficiency low.
Now the questions, how do i know if its the cat or the sensor(s)? How long do stock cats last on a stock car? Is there a way to test the 02 sensors or is it just a guessing game?
Last question, has anyone ever used these or heard any reviews on them?
http://www.mandrelexhaustsystems.com...EXHAUST/Detail
Theyre less than half the cost of the stockers from gmpartsdirect.
Are these something I can do in my garage without a lift? Im used to trucks where I can lay underneath easily.
Thanks
Could be a CAT issue at this point. No way to really test them. Good thing is that the rear O2 sensors don't affect driving at all. They are just there to monitor the effectiveness of the CATs. You could try a new sensor, or have the rear O2s disabled, but if your CAT is bad this will not help.
Try idling the car for about 10 minutes to let it warm up good. Look under the car to see if the CAT is glowing. If they are clogged up, they will get so hot they will glow.
Try idling the car for about 10 minutes to let it warm up good. Look under the car to see if the CAT is glowing. If they are clogged up, they will get so hot they will glow.
Joined: Nov 2001
Posts: 34,631
Likes: 2,557
From: Schiller Park, ILL Member: #317
These codes are fairly common on the '00-'02 V8 F-bodies, not sure if it's a common issue with the CTS-V. It doesn't actually indicate a clogged cat specifically, it just indicates an inefficient cat, usually the result of coatings wearing off the cat material causing them to have reduced oxygen storage capacity, and thus increased tail pipe emissions.
There is actually no code that directly indicates a clogged cat nor blocked exhaust flow. This code is just a product of the PCM comparing O2 readings between the pre and post cat O2 sensors, and the DTC will trip if the rear sensor readings respond too quickly and too closely in comparison to the front readings (indicating reduced oxygen storage capacity within the cat).
FWIW, my '02 has had this code for about a year now, and it happened just outside of the extended cat coverage that GM offered. I chose to do nothing about it, and just plugged in some old O2 sims I had, to keep the SES light off. It's been fine ever since, no clogged cats, no loss of power nor MPG, no driveability issues at all.
As yours is a CTS-V though, I'm not sure if there are other common known issues that may cause this code on that platform.
There is actually no code that directly indicates a clogged cat nor blocked exhaust flow. This code is just a product of the PCM comparing O2 readings between the pre and post cat O2 sensors, and the DTC will trip if the rear sensor readings respond too quickly and too closely in comparison to the front readings (indicating reduced oxygen storage capacity within the cat).
FWIW, my '02 has had this code for about a year now, and it happened just outside of the extended cat coverage that GM offered. I chose to do nothing about it, and just plugged in some old O2 sims I had, to keep the SES light off. It's been fine ever since, no clogged cats, no loss of power nor MPG, no driveability issues at all.
As yours is a CTS-V though, I'm not sure if there are other common known issues that may cause this code on that platform.
Thread Starter
On The Tree
Joined: Apr 2007
Posts: 165
Likes: 0
From: Bloomington, MN
I just hate covering stuff up like that though - true it works fine but I know its there. May as well put electrical tape over the CEL 
Hi-Flow Cats wouldnt be the worst thing and if it still happens I can put a new downstream 02 sensor in for about 40 bucks from rock auto.
Just wish someone would chime in about the quality of those magnaflow hi-flows from TrueBendz. Something about a company name with a z in place of an s screams cheap knock off garbage.
Hi-Flow Cats wouldnt be the worst thing and if it still happens I can put a new downstream 02 sensor in for about 40 bucks from rock auto.
Just wish someone would chime in about the quality of those magnaflow hi-flows from TrueBendz. Something about a company name with a z in place of an s screams cheap knock off garbage.
Joined: Nov 2001
Posts: 34,631
Likes: 2,557
From: Schiller Park, ILL Member: #317
If all you do is put tape over the light, then you'll never know if any other codes pop up over time. If you just disable the rear O2s, then you don't have this concern.
Joined: Nov 2001
Posts: 34,631
Likes: 2,557
From: Schiller Park, ILL Member: #317
They are devices that "simulate" rear O2 sensors, they plug into the wiring harness where the rear O2s would go. They aren't very popular any more, as most people use tuning software (such as HP tuners, LS1 Edit) to disable the rear O2s when cats are deleted. Something like this can be done at no additional charge during a dyno or even basic tune, so most people just go that route. Only a couple places still sell them, site sponsor Speed Inc is one of them. Retail cost these days is something like $90 or $100 for a pair, or you can find instructions on line to make your own, which ends up being far cheaper. Sometimes you can also find used ones for sale.
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TECH Senior Member
Joined: Apr 2002
Posts: 6,080
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From: So.Cal.
it steps the commanded AFR and it measures the response time of the rear O2 sensor wrt the front O2 sensor, if the time is too short it triggers the code P0420 (bank 1) or P0430 (bank 2)...
i.e. it is a problem with the cat and not the O2 sensor (if the O2 sensors were bad, the cat test never fails).
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Teching In
Joined: Jun 2012
Posts: 24
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From: Woodstock, GA
With an IR temp gun, measure the temp at the converter inlet and outlet. You should read between 50-100 degrees hotter at the converter outlet if the catalyst is reacting and doing it's job. If the temp is the same front to rear it is just blowing through. If it it hotter at the inlet it is clogged. Do not measure on the flange or the readings will no be accurate, read at the front and rear of the converter body.
