P0420 after 02 sensor change

[InfmousCornholio]

Vehicle: 2003 GMC Envoy XL
Engine: 4.2L I6
Mileage: 206,600 miles
Condition: Excellent
Auto trans

Issue: P0420 DTC

~1000 miles ago, the 02 sensor was changed when the light would come on. DTC codes indicated 02 sensor and "Bank lean" and all that. Light would come on, and turn itself off at various times.. which I have read indicates 02 sensor. So, 02 sensor was changed.

Just to be sure, I bought a code reader that could read GM, since my old one failed at that task. So, I purchased this. (For $40, it's amazing, and does what I need it to do.) Goldiger OM500 OBD II Diagnostic Scan Tool for OBDII Vehicles with full function

I also have a respectable arsenal of tools and wrenches, including 1/2" impact gun and sockets.. Too many to list here. They have nothing to do with this one, anyways.

We all also know what a Service Engine Soon light on a dash looks like. No photos or videos of this were taken.

Naturally, the truck runs better with the code off. No noises or sounds that are not supposed to be there. Put a CRC Guaranteed To Pass in the tank.. and some Seafoam in the oil. Truck needs an oil change soon, since the Change Engine Oil word (light?) comes on for 5 or 10 seconds after starting. And this within 1000 miles of its OCI sticker on upper left of windshield.. GM's OLM uses chemistry, not timer of miles? Good to know.

My understanding is that long highway trips and some WOT will help it. If I am wrong on that, tell me.

However, on this one, I'm not getting under the hood past changing oil and looking at things. I also found the brake booster line, for one of my favorite things to do. No rust or lack of tools for tires on this one. [censored] no. The opposite! Things untouched since 2003 here. Beautiful. Runs as new. Go GM...

In any case. Is there anything I can do, while driving this one, to help out the P0420?

Thanks.

Also, Happy Labor Day and Weekend to all.. Stay safe, I am headed to PA this weekend, working every night but Sunday night, and what can I say, I'm knee-deep in engine parts of my other two cars. A feat I'm sure indicates the world is ending.

 

[901Memphis]

The cat is probably out of spec

 

[Vikas]

The reason code P0420 is showing up now is because before that you had other code (either active or pending) so catalytic converter was no longer tested in the past. Once you fix the original problem, computer started to test of cat efficiency and it did not like the results.

The real solution is to replace the cat with the OEM one but that will cost you a *LOT* of money. Some donkeyhole might suggest putting new rear O2 sensor but don't listen to him. It is either new OEM converter or do the cheating like any red blooded American would do.

Google rear o2 sensor extension on ebay.

 

[simple_gifts]

Quote:

Some donkeyhole might suggest putting new rear O2 sensor but don't listen to him


My Toyota FSM suggests testing both O2 sensors as part of a diagnostic before replacing the cat. So if this were a toyota, the donkeyhole would be the person buying a $1200 part and installing before verifying the $70 one is working.

I replaced my front and rear O2 and it kept the light off for 50K miles.

http://www.easterncatalytic.com/education/tech-tips/the-misleading-nature-of-the-po42o-code/

 

[Bottom_Feeder]

I think there is also a general misunderstanding that 'a P0420 code means that the O2 sensor is bad'. While that may sometimes/usually be the case, the code is really reporting a converter issue which might actually be the problem.

 

[zvm77us]

what brand sensor, GM's are picky unless you use acdelco

 

[HerrStig]

The rear and front sensors have to "disagree" to keep the MIL light off which indicates the converter is working..reducing the HC leaving it. So, the reading can be showing a bad cat, but it can also indicate a bad front or rear sensor. It's been my experience that the front sensor is the one most prone to failure. There may be two front sensors on your engine, one for each bank. The only sure codes I have seen for sensor trouble are those for failure of the heater element on the four wire sensors which brings the sensor up to working temp, I have seen fronts get lazy enough to stall the engine without a mil reading. 200K on a front sensor is long service. OBD II is useful, but a meter, or better yet a scope on the sensor output is what's needed. If your engine is using a little oil, or running rich, the front sensors may foul without any other indication of trouble.

 

[901Memphis]

I have heard good things about Eastern cat in GM applications and cheaper than oem. I know for my application they make a specific high wash cat for the high failure rate of them.

Interestingly enough I had the same code on my Buick and I tried lots of things to fix it then one day my fuel pump died and I replaced it, to my surprise after I replaced the pump the code P0420 never came back! The cat that is on my Buick is just a generic XL style from a local muffler shop too.

While this probably isn't your issue I thought I'd share..

 

[cptbarkey]

MIL's 1999 subaru gets this code every 3 months, reset it and still driving happy.

 

[OVERKILL]

Originally Posted By: InfmousCornholio
Put a CRC Guaranteed To Pass in the tank.. and some Seafoam in the oil.


WHY???? if it "runs perfect" as you say, would you do this to somebody else's vehicle?

Originally Posted By: InfmousCornholio
GM's OLM uses chemistry, not timer of miles? Good to know.


No, it doesn't. It uses an algorithm.

Originally Posted By: InfmousCornholio
My understanding is that long highway trips and some WOT will help it. If I am wrong on that, tell me.


As long as you aren't the one going WOT with it and potentially blowing it up. If it runs fine, why does it need "help" ?

Originally Posted By: InfmousCornholio
However, on this one, I'm not getting under the hood past changing oil and looking at things.


Then:

Originally Posted By: InfmousCornholio
I also found the brake booster line, for one of my favorite things to do.


Are contradictory.

Originally Posted By: InfmousCornholio

Beautiful. Runs as new. Go GM...


Then leave it alone.

Originally Posted By: InfmousCornholio

In any case. Is there anything I can do, while driving this one, to help out the P0420?


No. If the catalyst is bad, it needs replacing or you need to "fool" the ECM with what Vikas mentioned in order for it to think it is OK.

Dumping solvent and pale oil in the oil and then down the brake booster isn't going to help.

 

[901Memphis]

CRC Guarenteed to pass actually has a good amount of PEA in it, i ran it a couple times when my P0420 was on and it didn't make it go out until i changed the fuel pump.

 

[Vikas]

Here is the thing.

It depends upon how bad the cat converter is. The P0420 trips very aggressively e.g. below 90% efficiency. The actual tail pipe emission would pass even at almost 50% efficiency.

When the converter is at or near 90% efficiency, the P0420 becomes erratic. You may be able to drive 100 or more miles before it may trip or not. If it is going to trip, it will usually trip when you let the gas pedal go after driving at steady high speed for a while. As a matter of fact, if you constantly drive like GearHeadTool (full gas or full brakes all the time), you can delay P0420 for a while!

Computer looks at the different pattern of front and rear O2 sensor. Usually slow failure of O2 sensors is that they get lazy rather getting overactive. When the converter starts loosing its efficiency, rear O2 starts following ront O2 and then computer trips the P0420 code. So it is in your best interest to have the rear O2 sensor lazy! That is why people telling to change rear O2 sensors are donkeyholes.

Obviously, the above analysis assumes that your engine has been running well and you have not poisoned the cat by dumping oil (aka oil burner) or dumping fuel (active missfire) on the converter.

 

[InfmousCornholio]

Originally Posted By: OVERKILL
Originally Posted By: InfmousCornholio
Put a CRC Guaranteed To Pass in the tank.. and some Seafoam in the oil.


WHY???? if it "runs perfect" as you say, would you do this to somebody else's vehicle?

Originally Posted By: InfmousCornholio
GM's OLM uses chemistry, not timer of miles? Good to know.


No, it doesn't. It uses an algorithm.

Originally Posted By: InfmousCornholio
My understanding is that long highway trips and some WOT will help it. If I am wrong on that, tell me.


As long as you aren't the one going WOT with it and potentially blowing it up. If it runs fine, why does it need "help" ?

Originally Posted By: InfmousCornholio
However, on this one, I'm not getting under the hood past changing oil and looking at things.


Then:

Originally Posted By: InfmousCornholio
I also found the brake booster line, for one of my favorite things to do.


Are contradictory.

Originally Posted By: InfmousCornholio

Beautiful. Runs as new. Go GM...


Then leave it alone.

Originally Posted By: InfmousCornholio

In any case. Is there anything I can do, while driving this one, to help out the P0420?


No. If the catalyst is bad, it needs replacing or you need to "fool" the ECM with what Vikas mentioned in order for it to think it is OK.

Dumping solvent and pale oil in the oil and then down the brake booster isn't going to help.


It would take soon much SeaGoam on the old sensor. Water clean, SeaFoam .. On new sensor, it doesn't want none. Lol.

Yes, I'm the WOTer. Top speed is 100MPH. Seems governor limited..

And I changed the oil yesterday. I even reset the OLM. I would post the videos, but they don't have anything to do with this code...

Salutations.

 

[OVERKILL]

So I'm guessing we are soon going to get a "guess the noise" thread where a rod bearing is going out of this thing?

You have an affliction where you can't stop until you love a vehicle to death. You have demonstrated that several times on this board under your myriad of aliases and a lot of these have involved vehicles belonging to others. This vehicle is no exception to that trend where the vehicle belongs to your mother. How do you think it is going to affect your relationship with her if (and the odds are high) you manage to destroy it?

 

[Nick1994]

Let's start the bets on whether or not this thing is going to make it another 6 months.

I'm saying no.

 

[kschachn]

Originally Posted By: Nick1994
Let's start the bets on whether or not this thing is going to make it another 6 months.

I'm saying no.


I'll wager 500 quatloos on the newcomer.

 

[silverrat]

Originally Posted By: Nick1994
Let's start the bets on whether or not this thing is going to make it another 6 months.

I'm saying no.


Heck his account won't last six months

 

[InfmousCornholio]

OK, so.

Are you.fine folks sayin that using CRC Guaranteed To Pass will NOT do anything to the cat, during the hundreds and hundreds if miles until Inspection sometime next month?

It won't help it flow better?

And stuff in the oil like Seafoam etc also won get burned off and help the Cat?

The light has been off for awhile.. I wonder if it's going to come right back on again during today's trip to get Antonio for the Honda, now that I said that.

Car has "no carbon anymore," I can tell because it doesn't shudder at all anymore when it turns off, it turns right off when key turned. This engine has/had issue in a TSB from GM over carbon deposits.

 

[InfmousCornholio]

Originally Posted By: InfmousCornholio

OK, so.

Are you.fine folks sayin that using CRC Guaranteed To Pass will NOT do anything to the cat, during the hundreds and hundreds if miles until Inspection sometime next month?

It won't help it flow better?

And stuff in the oil like Seafoam etc also won get burned off and help the Cat?

The light has been off for awhile.. I wonder if it's going to come right back on again during today's trip to get Antonio for the Honda, now that I said that.

Car has "no carbon anymore," I can tell because it doesn't shudder at all anymore when it turns off, it turns right off when key turned. This engine has/had issue in a TSB from GM over carbon deposits.


No one talked about Seafoam or the CRC Guaranteed To Pass, when I mentioned following up to help KEEP SES light off, etc... oh wealth of knowledge, oracle of information .

 

[InfmousCornholio]

Oh, nobody knows anything now

?