General Maintenance & Repairs - 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/servlet/the-273/04-dsh-07-CADILLAC-CTS-dsh-V-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.

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.

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.

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 :)

Only thing being covered up is elevated emissions levels. This is not a problem at all for me, but if you live in a sniffer state then I could see how this would eventually be a problem. This code would also need to be dealt with using either O2 sims or custom tuning if you were to install a catless exahust system, as many here do. To me, it's just not worth the cost of new cats since I have no sniffer test to pass.

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. :)

What are the sims you speak of? Something you have to make or are they off the shelf? How much do they run?

What are the sims you speak of? Something you have to make or are they off the shelf? How much do they run?

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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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?

...To trigger that code the PCM performs a very specific test...

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).

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.