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#2437476 - 11/17/11 04:31 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Quest Offline


Registered: 12/19/04
Posts: 6416
Loc: beaver land EH?
correction: rear O2 typically complains about CAT efficiency below threshold.


My bad on this part (thank you).

Q.
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#2437524 - 11/17/11 05:28 PM Re: P0420 Code... CAT or O2 sensors? [Re: Quest]
Trav Offline


Registered: 11/20/06
Posts: 9987
Loc: MA, Mittelfranken.de
The auto enginuity works great, some models need the enhanced modules.
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#2437758 - 11/17/11 08:56 PM Re: P0420 Code... CAT or O2 sensors? [Re: Trav]
vssjim Offline


Registered: 10/05/11
Posts: 350
Loc: McLean, Va.
This car probably has A/F sensors not 02's, and early 2000's Toyoata 2.4's had lots of Cat failures early in like just out of the 8year 80,000 federal warranty. probably is also a flash to fix this issue also.

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#2437768 - 11/17/11 09:06 PM Re: P0420 Code... CAT or O2 sensors? [Re: vssjim]
Quest Offline


Registered: 12/19/04
Posts: 6416
Loc: beaver land EH?
Originally Posted By: vssjim
This car probably has A/F sensors not 02's, and early 2000's Toyoata 2.4's had lots of Cat failures early in like just out of the 8year 80,000 federal warranty. probably is also a flash to fix this issue also.


@vssjim:

Different terminology but same deal: some folks call them A/F sensor(upstream/before CAT), I call it wideband O2 sensor Does it really matter?!?

Q.
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#2438359 - 11/18/11 02:56 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8246
Loc: NorthEast
For 2004 Toyota, it will be A/F for the exhaust manifold sensor(s). Generally, the one after converter are regular O2 sensor. The A/F sensors are expensive as compared to O2 sensors. A/F sensors give voltage which corresponds to the the oxygen content i.e. they give continuously variable voltage vs the regular O2 sensor which keeps on switching between low and high. The frequency of switching determines the oxygen content.

Bottom line is that if you get CAT efficiency low code (i.e. P0420/P0430) then that is what it is. The only trouble is at that stage, the efficiency is still far above what is necessary to pass the real emissions with flying colors (unless other parts need replacing and your engine is not running well).

You either have to fool the computer or you have to put a good quality CAT (OEM or similar) otherwise you will start getting the random P0420/P0430 codes which eventually starts tripping sooner and sooner.

Most consumer grade (and priced) OBD-II scanners (either standalone or PC/phone based) will NOT give access to all of the engine parameters. ScanGauge/UltraGauge gives you same (or similar) information. Only special purpose scanners ($$$$) with manufacture specific software ($$$$) will give you access to more live data. If you have VW/Audi, then you can get *everything* with RossTech scanner and there are lot of consumer priced scanners with (pirated??) RossTech. There are some cheap USB based oscilloscope currently on the market ($$$). Watching fuel trim data in the real time is generally useful but will not help in this particular case.

- Vikas


Edited by Vikas (11/18/11 02:58 PM)

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#2438450 - 11/18/11 04:47 PM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
stevejones Online   content


Registered: 02/13/11
Posts: 111
Loc: Midwest
Originally Posted By: Vikas
I strongly disagree with the previous responses. At 124K, it is your CAT which has become *SLIGHTLY* weak. Unfortunately the manufacturer has coded the computer to be very strict and thus you get the P0420 code. This is all a guess unless you do proper diagnosis using good scanner or better and oscilloscope.

If you want to change parts without doing that, then putting another OEM converter will fix it for next 100K miles. If you put an aftermarket, it will remain fix for next 5-10K miles before the light will come on.

There is a lot and I mean *LOT* of information available if you are willing to do the research on P0420.

- Vikas


$100 says this is the right answer.

I have a different make, but the same code @ around 130K. Honeycomb material was breaking up & rattling around. Replaced the cat with OEM, fine ever since. Now at 180K.


Edited by stevejones (11/18/11 04:47 PM)

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#2438474 - 11/18/11 05:11 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Thanks all for your wonderful input. I am just frustrated that it is so hard to tell what the "true" issue is. Aftermarket cats will run $500 for both, as this Toyota has two. They are only warranted for 5 years or 50k miles.

Also, I cleared the code the other day when I pulled it and it has not come back. What I need to do is look at the Emissions test from earlier this year to see how close it was to the "allowed limit" Unfortunately California is really strict on replacement of the cats - not unless it truly needs to be replaced.. I guess the shop you take it to determines if it really does need to be changed.

Since I am probably good for two or so years until I need another Smog Test, I may just let it ride until it really becomes a problem unless it will harm the engine or other components...
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#2438541 - 11/18/11 06:36 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
HTSS_TR Offline


Registered: 04/17/06
Posts: 12902
Loc: Irvine, CA
Failed Cat does not cause damage to the engine, it may not filter harmfull emission as good as a working Cat does. At worse, you are polluting the air a little more than normal.
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#2438647 - 11/18/11 08:12 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8246
Loc: NorthEast
As I said before if your car is in tune, even with P0420 code active, you will be well within the emission limits. Unfortunately, when the light is on, you fail the test automatically.

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#2439665 - 11/20/11 08:12 AM Re: P0420 Code... CAT or O2 sensors? [Re: HTSS_TR]
artificialist Offline


Registered: 09/23/07
Posts: 6899
Loc: Florida
Originally Posted By: HTSS_TR
Failed Cat does not cause damage to the engine, it may not filter harmfull emission as good as a working Cat does. At worse, you are polluting the air a little more than normal.

Failed cats can damage an engine.

When the core of a cat breaks apart and it is near the cylinder head, bits can be sucked back into the engine during cam overlap, and abrade the piston rings and cylinder bores, causing an early death.

Some Nissan engines had this problem.
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#2439712 - 11/20/11 09:16 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8246
Loc: NorthEast
Those are the so called pre-cats. Does any other manufacturer have them?

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#2439911 - 11/20/11 01:23 PM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
Trav Offline


Registered: 11/20/06
Posts: 9987
Loc: MA, Mittelfranken.de
Sure, look under any late 90's F Series/Expedition. EGR pipe is right there above the L side pre cat.
Over the years i have seen lots of pre cat equipped engines, the last years MG's were imported they had the cats bolted right to the exhaust manifold.
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#2440694 - 11/21/11 09:28 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Durango Offline


Registered: 02/15/07
Posts: 2045
Loc: Los Angeles, California
Originally Posted By: MysticGold04
2004 Toyota Highlander, 2.4L engine
124,xxx miles.. passed smog earlier this year

My wife was driving when the check engine light came on. I figured it was the gas cap, because I usually fill the tank for her, but she did this time. I had also just changed the air filter, so thought it might be a loose hose too. She kept driving with no issues to Reno, NV for the past weekend. I drove it home yesterday, no issues at all, same good gas mileage, etc. Checked the code, P0420 and cleared.. it will most likely come back.

any good recommendation for an aftermarket Cat? I have looked and the O2 sensors seem to be about $120 to $150 each.

How do I tell whether its the O2 sensors or the CAT?


MysticGold04,

When I had my 89' Camry with 250K miles on it the cat was good all those times. I don't think it's your cat since your truck is an 04" model year. Check your list of Toyota codes and see if there's a code for the 02 sensor. If it was the sensor then your computer should give you a specific code for it. Also bear in mind that computers can give false readings sometimes so anything is possible.

Durango

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#2440709 - 11/21/11 09:58 AM Re: P0420 Code... CAT or O2 sensors? [Re: Durango]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Originally Posted By: Durango

MysticGold04,

When I had my 89' Camry with 250K miles on it the cat was good all those times. I don't think it's your cat since your truck is an 04" model year. Check your list of Toyota codes and see if there's a code for the 02 sensor. If it was the sensor then your computer should give you a specific code for it. Also bear in mind that computers can give false readings sometimes so anything is possible.

Durango


Thanks for your reply. I am leaning to a false reading at this time, since I've cleared the code and it has not returned in over a week of driving. Dunno what to do at this point except to drive and see if it happens again. cheers
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'06 Focus SES 2.0 93,487 QSUD 5w30
'04 Highlander 2.4 157,521 Maxlife 5w30
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#2440713 - 11/21/11 10:03 AM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
I do have a scangauge II, but not with the programmable gauges. Is there anything I can check with it with the built in gauges? I suppose I could get the unit upgraded as well, which would give me access to more gauges, assuming the ECM supports them.
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'06 Focus SES 2.0 93,487 QSUD 5w30
'04 Highlander 2.4 157,521 Maxlife 5w30
"God is Great, Beer is Good, and People are Crazy." USA

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