I got this P0420 and i reset it to see if it returns to haunt me, anyone get this before? Any Suggestions? Catalytic coverters are quite the expensive piece.....

The catalyst is bad, that is about all there is to say about it.
That's the only reason a P0420 will set.
You can shop around but lots of times aftermarket cats will not have the correct materials in them and I have seen aftermarket cats set the codes just like the bad one you took out.

would it also be possible to have a exaust leak before the cat cause this ?

well i also read it can be an o2 sensorfault...also i reset the code it didnt come back...is that a good thing? maybe it could have had a bad flow and WOT cleaned it out? Let me know what you men think.

Would just removing the cat still throw a code?

most likely if the car was turned on before you replaced it. I just reset the code, maybe it was some sort of stupid issue and fooled the comp? To my knowledge is hasnt come back yet. Its been a day and about 15 miles of driving since.

Code came back up, changed the cat at cost of $280.

Good Choice!! I had a car with a bad cat one time. It was so plugged that the car would stop running now and then. Then it started on fire from heat. I don't know about you but I surely didn't like to sit back and watch my car burn. After A while I did put it out though...

hahaha yea man, i thought tid be alot mroe expensive.


that really sucks man was there any damage other than the cat

Oxygen entering before the catalyst would throw a lean exhaust code.
Bad O2 sensors would set codes for bad O2 sensors.
Removing the catalyst bed would obviously "reduce the efficiency" of the catalyst so yes it would set a code, and in a hurry.

The O2 sensors have to pass their diagnostic tests BEFORE the P0420 diagnostic is run so there are not many options except the catalyst itself.

It isnt just the cat...how many miles does your car have? can you hear rattleing if you bang on the cat? does it rattle when you throttle the motor? It can be a number of things..most likely its either an 02 sensor or an exhaust leak. Go to your dealer and just have them scan it and they can tell you what it is. They can block off the exhaust to see where the leak is and they can test the sensors independently. Also a new cat is around 110 generic.

More then likely its a crack in the pipe which will set off a below thresh hold on the cat since the 02 sensor isnt reading it properly. Thats what happened to my camaro.

who are you adressing?

A catalyst doesn't have to be broken to be bad. In fact I have seen catalysts that were broken that didn't cause a P0420 because they were still working.
I don't know how many times I have to say it, but bad O2 sensors set O2 sensor codes. The failure criteria for a P0420 are very specific and the computer has to see proper behavior from an O2 sensor in order to set the catalyst code.
A bad O2 sensor will not set a P0420, period, no matter how many times you say I am incorrect in thinking that.

Out of the 100 or so P0420 DTCs that I have gotten and repaired zero of them were due to exhaust leaks or O2 sensor failures.

Circuit Description
The powertrain control module (PCM) tests the ability of the catalytic converter to lower exhaust emissions. The PCM determines the performance of the catalytic converter by calculating the oxygen storage capacity. The PCM calculates this data by comparing the oxygen content of the exhaust entering the catalyst (read from the front and rear HO2 sensors) to that leaving the catalyst (read from the post HO2 sensor).

At the appropriate time, the PCM transitions the air fuel mixture from rich to lean or lean to rich depending on the current state of HO2S bank 1 sensor 2 (rich or lean state). Then, the PCM initiates a second, and opposite transition. The PCM compares the amount of time for the fuel control sensors to cross a calibrated threshold to the amount of time for HO2S bank 1 sensor 2 to cross the same threshold. The more time that is necessary for the HO2S bank 1 sensor 2 to cross the threshold, the higher the oxygen storage capacity. An HO2S bank 1 sensor 2 that crosses the threshold close to the same time as the front and rear HO2 sensors indicates a catalyst with low oxygen storage capacity, and DTC P0420 will set.

Conditions for Running the DTC
• DTCs P0030, P0036, P0101-P0103, P0106-P0108, P0112-P0113, P0117-P0118, P0121-P0123, P0130-P0135, P0137, P0138, P0140, P0141, P0150-P0155, P0171, P0172, P0174, P0175, P0201-P0208, P0300, P0335, P0336, P0340, P0341, P0351-P0358, P0385, P0386, P0404-P0405, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P0452-P0453, P0502-P0503, P0506-P0507, P1031-P1032, 1133-P1134, P1153-P1154, P1336, P1359-P1360, P1372, P1415-P1416, or P1441 are not set.

• The engine speed since the end of the last idle period is more than 800 RPM for a maximum of 46 seconds.

• The idle period is less than 60 seconds (1 minute).

• For non-California vehicles, the actual engine speed is within 100 RPM of the desired engine speed.

• For California vehicles, the actual engine speed is within 125 RPM of the desired engine speed.

• The engine run time is more than 10 minutes.

• The predicted catalyst temperature is between 420- 650°C (788-1202°F).

• The barometric pressure (BARO) is more than 75 kPa.

• The engine coolant temperature (ECT) is between 71-120°C (160-248°F).

• The intake air temperature (IAT) is between -6°C (21°F) and 200°C (392°F).

• The engine is in closed loop fuel control.

• The number of tests attempted during this ignition cycle is less than 6.

• The test attempted during idle period is 1.

Conditions for Setting the DTC
The catalytic converter efficiency is too low.

veyr sueful info thank you my good man

no problem.

I think it's tricky because everyone gets the idea that catalysts always fail the same way.
In fact there are several ways then can be "bad" and people get confused.

Always be sure to check the engine data for possible causes of a failed cat.
Fuel contamination is possible, could be you got a bad tank a long time ago and it started degrading the catalyst material until it couldn't do it's job anymore.

A catalyst doesn't have to be broken to be bad. In fact I have seen catalysts that were broken that didn't cause a P0420 because they were still working.
I don't know how many times I have to say it, but bad O2 sensors set O2 sensor codes. The failure criteria for a P0420 are very specific and the computer has to see proper behavior from an O2 sensor in order to set the catalyst code.
A bad O2 sensor will not set a P0420, period, no matter how many times you say I am incorrect in thinking that.

Out of the 100 or so P0420 DTCs that I have gotten and repaired zero of them were due to exhaust leaks or O2 sensor failures.
I sure didnt mean anything by it ....We had a STS-V get unloaded off the transporter and it immediately threw the po420..they worked with it for awhile , id come by and snoop around and lend an idea or two ...Next thing i knew they were after the left exaust manifold and had it out ....I aksed why since it was senosr related , they had told me "no its has to be a cracked manifold " ....i saw it held some validity , but i coudlnt figure out how it could crack a manifold from its awesome 1 mile journey from the factory to the dealership (cant crack it just hauling it on a truck)

as it turns out , and you being a tech at a dealership you are prolly aware of the O2 sensor harness recall ....turned out to be that ....LOL ...

I can't get to my service manual to recheck but I am reasonably sure that on STS-V the exhaust manifold has the catalyst in it as one assembly. I know SRX with a northstar is like this and although it's a little fuzzy I am reasonably sure that the XLR is the same too.
CTS-V is different because it's actually a Gen IV small block (chevy motor).
Those cats bolt on to the manifolds.
My point is, a cracked catalyst housing would definitey affect measured efficiency. Perhaps it was a misunderstanding on the part of the person who tried to explain it.

I apologize for coming off harshly. I have had problems with my temper lately and am actually working to learn to express myself better without being so bitter.
It's a slow process. I live on the defensive side of things because of my Dad.

I apologize for coming off harshly. I have had problems with my temper lately and am actually working to learn to express myself better without being so bitter.
It's a slow process. I live on the defensive side of things because of my Dad.
boy do i understand that !!! ive been workin on it for quite a few years , well about 5 ... slow process

Hey guys, I don't want to hijack this post but I have a question for ewill3rd and I don't have enough posts to send a private message. --------------------------------------------------------------------------------

I have a 2003 Cadillac cts with a check engine light. I took it to Auto Zone and had it scanned and it has two codes. One is a po420 catalyst efficiency below threshold bank 1 and a po430 catalyst efficiency below threshold bank 2. What could be the causes? It did the same thing about 2 weeks ago and the light reset itself. It came back on a few days later with the same codes. btw it has 94,000 miles. Thanks pw

pygmy, I just spotted this one.

Are you saying the codes were set and then you cleared them and they came back or are you saying you replaced the catalytic converters and then the codes came back?

If you cleared the codes and they came back that is a good indicator that you have some that won't pass the tests.
Since both of them indicate failures I would say that something has happened to the vehicle that ruined the converters.
Most often it is some sort of fuel contamination or someone used a type of sealant that is harmful to the catalyst materials.
The cats could just be worn out, but they are designed to last a good long time.

My suggestion would be to make sure there are no concerns present which might cause them to fail, be sure to use quality fuels and stay away from too many additives and get both converters replaced.... which is an expensive endeavor to say the least.
Sorry I missed this one earlier!
HTH.

I only cleared the codes. I have not replaced the cats. Would replacing the O2 sensors with mil eliminators stop the light from coming on? Thanks

Anyone?

Yes, tampering with the emissions system and violating federal law will probably keep the Check Engine light off.

:D
Or you could fix it ;)