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Anonymous_
Anonymous
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join:2004-06-21
127.0.0.1
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Reviews:
·Time Warner Cable

3 edits

catalytic converter? P0420

getting a new issue

catalytic converter code P0420

P0420 Catalyst System Efficiency Below Threshold (bank1)

I think the o2 sensor needs replacement because of the fuel regulator issue ,cause it to get "dirty" due to the rich mixture.

Not worried about passing smog since that is 9 months away

I had it reset to see if it comes back on maybe just a fluke.
Not getting any smoke out of the rear end tail pipe.

Please no tree hugger crap in this thread .

jsouth
Jsouth

join:2000-12-12
Wichita, KS

Re: catalytic converter? P0240

Could be.I wouldhavea shop place it on a scanner to narrow it down. My code turned out to be a bad egr valve.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

1 edit
reply to Anonymous_


99% of the time, a P0420 means you need to replace the deficient converter. O2 sensor failure *will not* cause the P0420 to set, but rather will give sensor failure codes. Monitoring the catalyst efficiency requires both the upstream and downstream sensors to be properly operating, so it is generally a very accurate failure code.

Nothing wrong with clearing it and seeing if it comes back, that's prudent.

EDIT: Dyslexia.....lol


cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7
reply to Anonymous_
Is the error P0240, or P0420? Catalyst system efficiency below threshold is P0420 although it seems that dyslexia on the internet is very common and they get flipped.

I'd visually inspect things to make sure that there isn't any damage to the O2 wiring harness, make sure the plug(s) are tight, etc as well as make sure there aren't any exhaust leaks, reset the code, and go from there.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3
That's funny, because the first reply I typed "P0420" then realized it didn't match his post and changed it. Guess my subliminal memory should have been obeyed.


Gordo74
Premium
join:2003-10-28
Monroeville, PA
reply to Anonymous_
P0420 on my Impala ended up being that there was a vacuum leak in the system near the gas tank. A tube came loose is all.
Expand your moderator at work


Cho Baka
Premium,MVM
join:2000-11-23
there
kudos:2
Reviews:
·TekSavvy DSL
reply to Gordo74

Re: catalytic converter? P0240

said by Gordo74:

P0420 on my Impala ended up being that there was a vacuum leak in the system near the gas tank. A tube came loose is all.

That makes no sense. Perhaps you have misremembered your code?
--
The talented hawk speaks French.


Anonymous_
Anonymous
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join:2004-06-21
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Reviews:
·Time Warner Cable
yeah it was p0420 got it rechecked had two entries on it. going to change out the sensor first to see if it fixes that. Since it's way cheaper then paying $1200 to replace it with a factory catalytic converter

New state law requires factory down to the exact model and production code. Other wise automatic fail.

If it was the catalytic converter I would be getting more codes besides the P0420

CEL was tripped when behind a diesel bus that was pouring out smoke.. assuming it was sucking craptastic air from the truck which caused it to trip .

and caused higher emissions from the car = CEL


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3
said by Anonymous_:

If it was the catalytic converter I would be getting more codes besides the P0420

What makes you think that? Your assumption in this case is wrong. P0420 is very often a stand-alone code, and requires no other associated failures to enable it.


Anonymous_
Anonymous
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127.0.0.1
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I was behind a bus that was pouring out a lot of smoke, when the CEL came on.


mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

1 edit

1 recommendation

said by Anonymous_:

I was behind a bus that was pouring out a lot of smoke, when the CEL came on.

You were behind a smoking bus *twice* to make it come on? You said you already had the code cleared once. And, that's a virtually impossible scenario to cause that code anyway.

What sensor do you plan on replacing on a blind guess? Upstream or downstream? I really don't understand why people want to come up with every reason under the sun why this code sets. There is a converter failure code so you want to replace the oxygen sensor. If a code sets for an cylinder #4 misfire, are you going to replace a headlamp?

I'm being straight here--- BOTH related-bank oxygen sensors MUST BE operating properly for this failure code to occur. The computer is measuring exhaust oxygen content BOTH before AND after the catalyst to determine its efficiency. A malfunctioning O2 sensor strictly prevents this diagnostic cycle from running, and will set a SENSOR failure code, NOT a catalyst code. There are no "false positives" here.

I will add that the best course of repair is proper diagnosis. Get the system tested, preferably by a shop that can scope the components to get the correct picture. Like I said, very high percentage its the converter. Oxygen sensor failure is very rare.


Anonymous_
Anonymous
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Reviews:
·Time Warner Cable
said by mattmag:

said by Anonymous_:

I was behind a bus that was pouring out a lot of smoke, when the CEL came on.

You were behind a smoking bus *twice* to make it come on? You said you already had the code cleared once. And, that's a virtually impossible scenario to cause that code anyway.

What sensor do you plan on replacing on a blind guess? Upstream or downstream? I really don't understand why people want to come up with every reason under the sun why this code sets. There is a converter failure code so you want to replace the oxygen sensor. If a code sets for an cylinder #4 misfire, are you going to replace a headlamp?

I'm being straight here--- BOTH related-bank oxygen sensors MUST BE operating properly for this failure code to occur. The computer is measuring exhaust oxygen content BOTH before AND after the catalyst to determine its efficiency. A malfunctioning O2 sensor strictly prevents this diagnostic cycle from running, and will set a SENSOR failure code, NOT a catalyst code. There are no "false positives" here.

I will add that the best course of repair is proper diagnosis. Get the system tested, preferably by a shop that can scope the components to get the correct picture. Like I said, very high percentage its the converter. Oxygen sensor failure is very rare.

I'll just wait tell I need to do the smog test (you bet I going to clear the code before I get the test done)

if it passes then it's a faulty SENSOR. if it fails I get it fixed
--
Well, does your car at least turn into something else? Sometimes I turn it into a trashcan. Hmm...

bgraham

join:2001-03-15
Smithtown, NY
reply to Anonymous_

Re: catalytic converter? P0420

The OP would be wise to listen to the advice of mattmag. I too decided against paying $1200 for the OEM Buick cat and went to Rockauto and paid $200. Exactly a week after the 12 mos warranty expired I started getting a PO420 about every other week. Googled the problem and there is a lot of issues with PO420 and cheap replacement cats. Replacing the cat is the only answer.

I will add that I replaced the original OEM cat at 100k miles due to it being blocked.

telco_mtl

join:2012-01-06
reply to Anonymous_
said by Anonymous_:

getting a new issue

catalytic converter code P0420

P0420 Catalyst System Efficiency Below Threshold (bank1)

I think the o2 sensor needs replacement because of the fuel regulator issue ,cause it to get "dirty" due to the rich mixture.

Not worried about passing smog since that is 9 months away

I had it reset to see if it comes back on maybe just a fluke.
Not getting any smoke out of the rear end tail pipe.

Please no tree hugger crap in this thread .

i bought a 02 grand prix with a hollowed out cat and it was throwing this code, my 97 grand prix also threw it. replacing the cat fixed it.

telco_mtl

join:2012-01-06
reply to mattmag

Re: catalytic converter? P0240

said by mattmag:

said by Anonymous_:

If it was the catalytic converter I would be getting more codes besides the P0420

What makes you think that? Your assumption in this case is wrong. P0420 is very often a stand-alone code, and requires no other associated failures to enable it.

exactly, like i just posted, faulty cats threw that code on my both grand prix. same car as the impala, and those were the only codes i had


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2
reply to Anonymous_

Re: catalytic converter? P0420

I have had a P0420 code once. It was indeed a failed converter. Luckily, the converter was still under warranty.
--
Shine on you crazy diamond...


Anonymous_
Anonymous
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·Time Warner Cable
going to get it fixed but later this year when it's time to smog.

FACTORY replacement is required to pass.

otherwise getting a after market is throwing money into a money pit.
--
Well, does your car at least turn into something else? Sometimes I turn it into a trashcan. Hmm...


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2
How many miles on the car? By federal law, cats are required to be covered for 8 years/80K miles on cars from 1995 and later.
--
Shine on you crazy diamond...

Formeister

join:2000-10-28
Somers, CT
reply to Anonymous_
said by Anonymous_:

I think the o2 sensor needs replacement because of the fuel regulator issue ,cause it to get "dirty" due to the rich mixture.

I've heard that rich mixtures will cause cats to overheat and kill them.

telco_mtl

join:2012-01-06
reply to Anonymous_
said by Anonymous_:

going to get it fixed but later this year when it's time to smog.

FACTORY replacement is required to pass.

otherwise getting a after market is throwing money into a money pit.

just curious, where are you? can you get a used one from a jurisdiction that doesnt have rules about selling used cat's


Gordo74
Premium
join:2003-10-28
Monroeville, PA
reply to Cho Baka

Re: catalytic converter? P0240

said by Cho Baka:

said by Gordo74:

P0420 on my Impala ended up being that there was a vacuum leak in the system near the gas tank. A tube came loose is all.

That makes no sense. Perhaps you have misremembered your code?

I never said it made sense, but repairing the vacuum leak made it go away and MPG returned to normal.


Anonymous_
Anonymous
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join:2004-06-21
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Reviews:
·Time Warner Cable

4 edits
mileage is sloppy been getting 18MPG city(@near highway speeds 45-65mph ) and 23MPG on the freeway.(very hilly though)

before the fuel regulator went out I was getting 17/22
when the fuel regulator was dead 9MPG/15MPG
(No visible smoke with the "rich mixture")

Not getting any visible smoke from the tail pipe.
using 1 qt of oil every 2,000-2100 miles which is at manufacture specification.

I use 89 octane fuel
engine runs quieter over all with this fuel.

engine Is running warmer then normal (but still with in the normal accepted rage aka the middle)

But I think it still should be less since it is winter and is fairly cold outside mid 40's

Ones in bold might be the possible issue

A code P0420 may mean that one or more of the following has happened:
Leaded fuel was used where unleaded was called for

A damaged or failed oxygen sensor (HO2S)
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
Retarded spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings
Leaking fuel injector or high fuel pressure


Cylinder misfire
Oil contamination


Cho Baka
Premium,MVM
join:2000-11-23
there
kudos:2
Reviews:
·TekSavvy DSL
That is a funny list. I googled it, and in the first hit it seems to have been posted in the comments on an Amazon sale for an O2 sensor.

The second link, »www.obd-codes.com/p0420 , has these 2 gems:
"Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit."

Go ahead and replace that sensor if you want. It isn't my money you are burning.
--
The talented hawk speaks French.

Formeister

join:2000-10-28
Somers, CT
P0420 Catalytic efficiency below threshold value.

My daughter's 1998 Accord threw this code twice, about two years apart. The first time I guessed and didn't test the 02 sensor, just replaced the easiest sensor to reach, the one after the cat and code cleared. Two years later, same code. Naturally, I replaced the inlet O2 sensor this time. Code cleared. Car sold three years later with original cat and 240K miles.

The cat converter efficiency can only be measured by two O2 sensors: in and out.

So, I would test each O2 sensor as they are so easy to remove, before I'd spend a bunch on a new cat.

BTW, there are thermal tests that can be done on a cat to determine if it's functioning correctly but most home owners don't usually have the thermocouple sensors and meters.

Cats do fail, I've just never seen it on many high (>200K mile) cars that I have driven, ymmv.


Anonymous_
Anonymous
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join:2004-06-21
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Reviews:
·Time Warner Cable

1 edit
reply to Cho Baka
said by Cho Baka:

That is a funny list. I googled it, and in the first hit it seems to have been posted in the comments on an Amazon sale for an O2 sensor.

The second link, »www.obd-codes.com/p0420 , has these 2 gems:
"Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit."

Go ahead and replace that sensor if you want. It isn't my money you are burning.

Thanks the light went off, after I smacked the catalytic converter, with a rubber mallet.
saved $1400 doing that. 150miles+ no light

Now I have to deal with the thermostat... since it's overheating now, to keep it under the 1/2 point I drove it 150 miles with the heater on and windows & moon roof open)

coolent is full maybe it has some air in the system or thermostat is failing ?

yes it has coolant in it


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2
Hmmm.... a clogged cat can also cause excessive back-pressure which can lead to overheating.


Anonymous_
Anonymous
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join:2004-06-21
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Reviews:
·Time Warner Cable

3 edits
said by rockotman:

Hmmm.... a clogged cat can also cause excessive back-pressure which can lead to overheating.

100% "clear" air comes from the tail pipe. a lot of it
before I was getting 22-23mpg highway

Now gas mileage shot up was getting 35MPG (300miles round trip total) (computer claimed 45MPG average though.)
80 to 99 (inst mpg)


Lagz
Premium
join:2000-09-03
The Rock
Hmmm .. p0420 and a rough idle.
»03 impala idle issues
2 + 2 = 4


Anonymous_
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that was the fuel regulator