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#2435399 - 11/15/11 04:09 PM P0420 Code... CAT or O2 sensors?
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
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?
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#2435425 - 11/15/11 04:31 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Trav Offline


Registered: 11/20/06
Posts: 10249
Loc: MA, Mittelfranken.de
Eastern makes very high quality cats.
Using an infrared thermometer check the temp before and after the cat look for at least 30f, some use to say 100f but some newer engines run so clean there is not that much difference.

Check the coolant temp sensor, there maybe 2 one for the light/gauge and one for the ECM, check the one for the ECM, they usually throw a code if failed but one reading low may not.
Also look for any exhaust leaks before the cat, manifold, pipe etc. Any ingestion of fresh air pre O2 with throw it for a loop.
You really need a scan tool to diagnose this properly, being able to see O2 wave forms and fuel trim is a must, it can also see the other sensors and get a complete picture of what's going on.
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#2435447 - 11/15/11 04:58 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
hypervish Offline


Registered: 04/20/10
Posts: 1530
Loc: new jersey
Usually it's the 02 Sensor, rarely do the CAT's go bad.


Edited by hypervish (11/15/11 04:58 PM)
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#2435452 - 11/15/11 05:04 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
simple_gifts Offline


Registered: 07/26/04
Posts: 9120
Loc: Middlesex County CT
My !echo! factory manual indicates you can test the O2 sensors with a multimeter. I did not bother and just replaced both of them. (direct fit denso from rockauto) I can't find my factory manual, but will look for it; the procedure is well documented.

I believe the flowchart procedure was

1) verify no exhaust leaks.
2) Check resistance on both O2 sensors (don't know what they "should" read until FM is found)
3) replace cat.

obviously stopping if one of these steps fixes the issue; I disconnected the battery after I performed step #2.


Edited by simple_gifts (11/15/11 05:05 PM)
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#2435469 - 11/15/11 05:26 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
simple_gifts Offline


Registered: 07/26/04
Posts: 9120
Loc: Middlesex County CT
http://www.bobistheoilguy.com/forums/ubb...rue#Post2261600

Here is my thread; look @ comments by Bill in Utah.


Edited by simple_gifts (11/15/11 05:27 PM)
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#2435613 - 11/15/11 07:01 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MarkM66 Offline


Registered: 10/19/10
Posts: 1209
Loc: stl
If you really want to be cheap, the old spark plug anti fouler 02 spacer would probably keep that code from coming back.

Not sure if it'd get by your smog check out there though.

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#2435628 - 11/15/11 07:11 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Quest Offline


Registered: 12/19/04
Posts: 6475
Loc: beaver land EH?
IMHO replace the O2 sensors first (pre-cat ones, wideband with pre-heater built in). Get the Denso ones from Rock Auto and if that resolves the problem, then you are all set.

I concur that cat rarely has to be tackled at this stage, mainly O2 sensors.

I don't buy those universal ones that require you to splice it to make it fit. Many a times: it would get you in a very difficult position (like engine would behave oddly even after replacing the O2 sensors with non-OE aftermarket ones).

Q.
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#2436103 - 11/16/11 08:39 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
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

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#2436225 - 11/16/11 11:12 AM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
Trav Offline


Registered: 11/20/06
Posts: 10249
Loc: MA, Mittelfranken.de
I was with you until this..
Quote:
If you put an aftermarket, it will remain fix for next 5-10K miles before the light will come on.


This is simply painting all aftermarket cats with the same broad brush. Many aftermarket cats are junk that's true enough but not all.
Eastern make many OEM cats and sells the same quality even CARB approved and problem vehicle cats.
I put one in a Solara 65K ago and no problem with performance or corrosion.
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#2437173 - 11/17/11 11:07 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Ok.. here is my thinking, please correct me if I seem wrong in my logic...

Good gas mileage as always - Not the upstream O2 sensor
No hesitation/engine runs strong - Not the Cat

Downstream O2 sensor is failing or failed. Does this seem correct? Aside from checking for exhaust leaks, etc. it seems like the next logical step. At least to me.. a new Denso sensor from Rockauto is $118.
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#2437187 - 11/17/11 11:21 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Quest Offline


Registered: 12/19/04
Posts: 6475
Loc: beaver land EH?
@ MysticGold:

CAT is only responsible for post-combustion exhaust scrub before the gas is vented.

So long as your engine is in good shape (ignition timing, etc.) and the cat matrix hasn't collapsed, there shall never be any perceivable drivability issues detectable.

I'd recommend you to do the following first:

(a) get FSM or similar to find the proper means to test/verify that the downstream (post-CAT) O2 sensor is still within spec?

Once that is done, go get an OBD-II scanner capable of freezeframe (ScanGauge works wonders also) and to monitor and capture some of the values over fuel trim, etc. (snippet obtained from one of the ToyotaTech postings):

P0420 - Catalytic Efficiency under threshold.
RPM: 1944
38.0% Load Value
Coolant 188 degrees
87 degree intake temperature
3.1% Short Term Fuel Trim 1
14.0% Long Term Fuel Trim 1
-100.6 Short Term Fuel Trim 3
-100.6 long Term Fuel Trim 3
49 miles per hour
Fuel System 1: Closed



and post them here to discuss.

Don't discount the possibility of a "hiccup" on the OBD-II monitoring part and simply by clearing the P-0420 code would have resolve this matter entirely w/o even calling on parts replacement...

Q.

a casual reference: http://www.yotatech.com/f2/p0420-code-details-does-mean-anything-anyone-tech-145496/
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#2437227 - 11/17/11 12:05 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Trav Offline


Registered: 11/20/06
Posts: 10249
Loc: MA, Mittelfranken.de
Quote:
Good gas mileage as always - Not the upstream O2 sensor

The problem with upstream O2 sensors is there is one of them or two if its a V engine (generally speaking, posters please don't bombard the tread with odd balls that may use 4 or 1 for each double bank).

This means that if for example 1 cylinder is getting more fuel the ECM with lean all the others on that bank down to achieve an average as close to stoichiometric as possible. Basic overall fuel delivery amount will be the same but the 3 other cylinders will actually be running somewhat lean. This on going state of confusion can cause issues in other parts of the system.
On the other side if one cylinder is lean for some reason the ECM with richen the others. Again because one is less and the others are richer the average fuel deliver amount remains the same.

The only way to prevent this averaging would be to use an upstream and a downstream sensor for each individual cylinder.

Quote:
No hesitation/engine runs strong - Not the Cat


True if the cat was plugged otherwise no. If the wash coat is damaged or gone but the cat is not plugged it will not effect performance.

Quote:
Downstream O2 sensor is failing or failed. Does this seem correct?

The downstream sensor looks for a difference from the upstream sensor therefore verifying catalytic action took place.
In principal the closer the numbers are to each other the less efficient the cat is.

A weak front sensor may not throw a code but may not be signalling reliable information.
For this reason i said a comprehensive view using a scan tool is important for correct diagnosis. Throwing parts at an issue like this is a mugs game at best.
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#2437401 - 11/17/11 03:08 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
Computer creates (or observes) condition under which it knows that cat has to "work". Typical condition is when you take the feet off the gas pedal while driving at highway speeds. If other conditions are "correct", then computer decides to "test" you catalytic converter. It compares cross counts (number of swings of the O2 sensor voltage from high to low to high etc) of front (i.e. before the cat) and rear (after the cat) sensors. It wants to see lot less (i.e. 10 times less) on the rear sensor than on the front. Now it knows that your cat is doing its job. It will start throwing the code if instead of 10 times less it is only 9 times less. HOWEVER, the actual emission will still way below the federal limits IF your car itself is in good tune.

When O2 sensor starts failing, it will NEVER (well, almost never) become faster i.e. more cross counts. It usually becomes sluggish. That is why very rarely rear sensor replacement is ever a cure for P0420/P0430.

Quest; can you explain how the freeze frame data is going to be useful in case of P0420/P0430 ? The fuel trim numbers do not trip that code. The cross counts are not in the freeze frame. If your scanner can do live data or better, graphs, you have a chance of catching them in the act but it will not be easy unless your car supports newer faster refresh protocol along with the fast scanner. Older protocol such as the ISO update speed is too slow to get good O2 switching graphs.


Edited by Vikas (11/17/11 03:14 PM)

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#2437440 - 11/17/11 03:47 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 15279
Loc: Sunny Florida
Just take that rear one out and pack it in some steel wool.

Works sometimes.

We simply read the actual voltage at the sensor. If it's out of range replace it.
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#2437456 - 11/17/11 04:07 PM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
Quest Offline


Registered: 12/19/04
Posts: 6475
Loc: beaver land EH?
Originally Posted By: Vikas
Computer creates (or observes) condition under which it knows that cat has to "work". Typical condition is when you take the feet off the gas pedal while driving at highway speeds. If other conditions are "correct", then computer decides to "test" you catalytic converter. It compares cross counts (number of swings of the O2 sensor voltage from high to low to high etc) of front (i.e. before the cat) and rear (after the cat) sensors. It wants to see lot less (i.e. 10 times less) on the rear sensor than on the front. Now it knows that your cat is doing its job. It will start throwing the code if instead of 10 times less it is only 9 times less. HOWEVER, the actual emission will still way below the federal limits IF your car itself is in good tune.

When O2 sensor starts failing, it will NEVER (well, almost never) become faster i.e. more cross counts. It usually becomes sluggish. That is why very rarely rear sensor replacement is ever a cure for P0420/P0430.

Quest; can you explain how the freeze frame data is going to be useful in case of P0420/P0430 ? The fuel trim numbers do not trip that code. The cross counts are not in the freeze frame. If your scanner can do live data or better, graphs, you have a chance of catching them in the act but it will not be easy unless your car supports newer faster refresh protocol along with the fast scanner. Older protocol such as the ISO update speed is too slow to get good O2 switching graphs.


@ Vikas,

Your observation RE: rear 02 sensor replacement rarely cures the P-0420 issue, and if that O2 sensor ever throws you a code is noted; it's typically complains about O2 efficiency below threshold and nothing more.

I understand that the crosscount will not become faster.
My current OBDII scanner is basically a scangauge on-loan to me to deal with anything circa 2002 or newer (older one, from 96 ~around 2003 are handled by my Equus OBD-II scanner). I figure that the newer ones may be able to report the fuel-trims, etc. in real time mode so as to report the situation better, and my focus of the obeservation is still on the front O2 sensor part in relation to that to the other variables, not so much as to reporting on the post-cat O2's efficiency.

maybe a freezeframe capable OBD-II scanner isn't all that useful in dealing with this subject matter, afterall.


To really watch how well the front (wideband O2) sensor behaves is to have it rigged to an oscilloscope, and run the engine, something that may be beyound most home/DIYer based auto repair.

My next major spending would be a computer (laptop) based OBD-II scanner interface with the ability to monitor various different variables "live" and infinitely code upgradable. That would helps in diagnosing a lot of difficult to repair problems revolving OBD-II systems.
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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: 6475
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: 10249
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 Online   content


Registered: 10/05/11
Posts: 351
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: 6475
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: 8317
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 Offline


Registered: 02/13/11
Posts: 113
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: 12961
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: 8317
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: 6935
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: 8317
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: 10249
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: 2050
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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#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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#2440732 - 11/21/11 10:26 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Trav Offline


Registered: 11/20/06
Posts: 10249
Loc: MA, Mittelfranken.de
Take a look at this, i would try to rule out as many things as possible before spending any money.

http://www.easterncatalytic.com/education/EC570_MA_11_10_TT_final.pdf
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#2440745 - 11/21/11 10:45 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
You probably have many months of driving before the P0420 code is going to start coming more often. Wait until that happens. Even if your ScanGauge were to give you front and rear O2 readings, it will be still difficult to check the health of the converter. You can either watch the readings or watch the road, I prefer you do the later :-) You really want a graphing scanner or better an oscilloscope. Your 2004 is most like NOT an CAN capable vehicle, so the refresh rate is going to be slow.

- Vikas

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#2441334 - 11/21/11 09:30 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
wiswind Offline


Registered: 11/03/04
Posts: 1011
Loc: Wisconsin
I looked the catalytic converter for 2004, 2.4L Highlander up on toyotapartszone and the list price for OEM (Toyota) is $585 for vehicles manufactured up to 08 of 2003 (their price is about $512) and from 08 of 2003 and newer, the list price is $392 (their price is $343).
You would need to enter your Vehicle Identification Number (VIN) in order to find out which part is for your vehicle.
There are other websites for genuine Toyota parts.....I used the one I mention because they USED TO have very detailed diagrams, which don't seem to be there now.
I have not seen such detailed diagrams outside of a dealership parts computer.

I went aftermarket on a vehicle (FORD) where the OEM was listed at $1600 and the best price that I could find was $1200.
If these prices are correct (you only need 1 of these), then you are not saving much by going with a QUALITY aftermarket.

I have the 1MZFE V6 in my 2003 Sienna, and it has the "pre-cat's" that were mentioned.
There are TSBs from TOYOTA about problems with the P0420 for my vehicle (remember, different motor) and it could be cat, oxygen sensor or even the ECM (computer), with the computer being $$$$
It was not a computer problem that could be solved with a reflash, the unit had to be replaced.
This leads me to believe that the sysetem is running pretty close to the limits that the computer permits.

That said, I would wait and see if the code comes back.....and go from there.
It would be great if you could find a shop where they apply brains and the right equipment to the job, but so many places just throw parts at it until the problem goes away....often causing you to make return trips and spend more money than necessary.

Also, the statement about the Air/Fuel sensors, aka wideband oxygen sensors, those before catalytic converter sensors are quite expensive.
After reading the TSB about the P0420 for my vehicle....and reading other posts in a couple of forums, I am even more driven to stick with OEM (or the same Denso cross for OEM)for these particular parts.

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#2442833 - 11/23/11 01:21 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
dailydriver Offline


Registered: 03/14/06
Posts: 7157
Loc: Bucks County, Pa.
Does Cali check for I/M Readyness codes, and fail you if there is more than one (or ANY) incomplete??
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#2545161 - 02/22/12 03:05 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Ok.. the wife just got back from Reno this past weekend and said the engine light came on again.. this is the first time it has come back since I reset it earlier in this thread. My guess is it had been several thousand miles.

I need to scan the code again with my scangauge and I'm willing to bet dollars or doughnuts that it is again a P0420.
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#2545275 - 02/22/12 04:56 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
LeakySeals Offline


Registered: 02/18/11
Posts: 5070
Loc: MA
Been through it. Your CEL is set to 95% (cats almost perfect) Pull the rear 02 out and add a spark plug anti fouler. youtube it. That will give you many more years.
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#2545889 - 02/23/12 10:53 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
But he is in CA and I am under impression that emission stations are all state owned and do a thorough job and extender could be visible. Also in CA, the car is actually put on the dyno and tested for emissions. Google for anti fouler usage in California and see if others have done it in the past. In most other states, they hook up the scanner and that is all they do for emission test but NOT in California.

To OP:- The P0420 (and/or P0430) code would eventually start appearing more often. Since it is on the borderline, you will be getting the code randomly. You will think it has to do with the gas, ambient temperature and convince yourself that changing the gas station has fixed it. You could go for hundreds of miles until it trips again. Believe me, I had driven my vehicle(s) with scanner connected all the time and taken it on long trips and have reset the code while driving. I was getting good at erasing the code one handed without taking my eyes off the road. My fingers had memorized the key code sequence needed for that task.

It is given that by the time your next inspection is due, it will trip pretty much within 20 miles of resetting it.

Find a shop which specializes in emission and has tools such as scope to graph the sensor output and scanners to look at Mode 6 tests results. Sometimes, borderline Mode 6 test results would be able predict if the code is eminent or not.

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#2545947 - 02/23/12 12:08 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
bdcardinal Offline


Registered: 06/03/05
Posts: 6678
Loc: Santa Barbara, CA
Emissions stations in CA are not state owned. They are all independent, but the process to get the smog license is a PITA.
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#2551946 - 02/28/12 11:44 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
I'm going to scan the last smog check and post it. Then you guys tell me what you think about it. ok?
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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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#2551963 - 02/29/12 12:36 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
mrcoolguy Offline


Registered: 12/14/11
Posts: 189
Loc: Los Angeles
My car throws P0420 and P0430 codes...but thats because my car doesn't have any cats wink
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#2552746 - 02/29/12 07:09 PM Re: P0420 Code... CAT or O2 sensors? [Re: mrcoolguy]
dailydriver Offline


Registered: 03/14/06
Posts: 7157
Loc: Bucks County, Pa.
Originally Posted By: mrcoolguy
My car throws P0420 and P0430 codes...but thats because my car doesn't have any cats wink


There are tuners (actual people, NOT hand held devives) using EFI Live and such who can write those codes out of your ECM (if you are speaking of your f body).

But that will not do you any good in draconian Cali, since they also do gestapo-like visual inspections for actual, real, functional catcons and hooked-up rear O2s, as well as on-dyno sniffer tests. frown
_________________________
2000 Z28 1SC 6 speed 175K miles
Red Line 0W-40/Sustina 0W-20 (20/80 mix)
Fram Ultra filter
Synpower 75W-140/4oz. XL-3
Red Line D4 in the T56

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#2552793 - 02/29/12 07:44 PM Re: P0420 Code... CAT or O2 sensors? [Re: dailydriver]
mrcoolguy Offline


Registered: 12/14/11
Posts: 189
Loc: Los Angeles
Quote:


There are tuners (actual people, NOT hand held devives) using EFI Live and such who can write those codes out of your ECM (if you are speaking of your f body).

But that will not do you any good in draconian Cali, since they also do gestapo-like visual inspections for actual, real, functional catcons and hooked-up rear O2s, as well as on-dyno sniffer tests. frown


Yeah, I am going to get some goodies first ( LS6 intake, heads, cam, LT headers and ORY pipe before I get a tune). I will have to pay for it to be street legal LOL laugh [censored] Cali ... frown
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05 Civic I4 109K M1 AFE 0W20
03 Civic 80K M1 AFE 0W20
97 Avalon V6 146K M1 0W40
00 Camry I4 106K M1 EP 5W30

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#2557755 - 03/05/12 12:00 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Ok.. I want to try to diagnose this myself if possible. I should have some time this week to pull the code.

I am just wondering... I have a scangauge II, but it is not the updated version with the XGauge capability. Do/can any of you who have one of these scanners look at the O2 sensor data with it? I will spend the $25 to upgrade mine if that is possible. Or, I could try to sell that and get a more advanced scanner for around $200 that will read the O2 data. I called a local shop and they told me labor just to find out who/what the culprit is would be $100... I can easily change out the sensors myself - hoping this is the issue!
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'06 Focus SES 2.0 93,487 QSUD 5w30
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#2557846 - 03/05/12 01:12 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
JamesBond Offline


Registered: 12/13/06
Posts: 379
Loc: midwest
I've posted this info in other threads re. P0420 codes and will offer my 2 cents about what has worked for me. Your cat and secondary O2 sensor probably do not work as well as they did when new causing an occasional check engine light. Before I replaced either part I would dump a bottle of techron, or regane in the tank, warm up the car and put the trans in 2 and do some alternating high throttle and coasting between 30 and 50 mph up and down a country road or some such safe place. After 8-10 reps of this I would hit the highway for 10 miles or so then come back and repeat the process. The goal of this would be to get the exhaust system and cat plenty hot in order to burn off any deposits in the cat or on the O2 sensor. It also couldn't hurt to do the plugs and clean the throttle first if they haven't been done. Then reset the light if it doesn't go out on its own.

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#2557895 - 03/05/12 02:04 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Vikas Offline


Registered: 07/22/05
Posts: 8317
Loc: NorthEast
The answer was posted here multiple times.

The cheapest scanner to verify weak catalytic converter costs $14.50 assuming you already own an Android platform such as a Smartphone or Tablet. It will just confirm the diagnosis of your converter falling off the the so called 95% efficiency cliff with 99% accuracy. There is a 1% chance that your primacy O2 sensor could be bad.

LicenceToKill:-
Can you tell me how long it has been since you used your method to get rid of P0420?

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#2558433 - 03/05/12 10:17 PM Re: P0420 Code... CAT or O2 sensors? [Re: Vikas]
TFB1 Offline


Registered: 09/03/10
Posts: 2622
Loc: VA
Here's how to fix that P0420...


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#2558481 - 03/06/12 12:01 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
ok.. so I found the last smog check.. done on 7/20/10 so it will most likely have to be tested again in July as CA does biannual inspections.

Here were the readings - keep in mind they put cars on the dyno.

15MPH Test: RPM@1794 HC PPM:37 (MAX:50) C0: 0.27 (MAX 0.64) NO PPM:444 (MAX:508) PASS
25MPH Test: RPM@1765 HC PPM:9 (MAX:34) C0:0.00 (MAX 0.78) NO PPM:22 (MAX:761) PASS

does it seem like the converter either wasn't fully warmed up... or does it seem to need replacement? Or can you even tell from these results?

I priced sensors today.. about $220 for both upstream and downstream Denso (OEM style sensors)
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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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#2558586 - 03/06/12 06:41 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
Trav Offline


Registered: 11/20/06
Posts: 10249
Loc: MA, Mittelfranken.de
Its hard to tell from these reading if there is any problem.
IMHO keep this as simple as possible. O2 sensors do get slow, in fact for many years some companies recommended 30K change intervals.
Today they can go much longer but personally over 100K i change them if i suspect a problem.

Whenever you change a cat its a good idea to swap them out anyway especially if they are in the 100k range, so swapping the O2's first makes sense.
If that doesn't cure the problem then you can change the cat. +1 on the Denso O2's, they are quality units.
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#2559034 - 03/06/12 01:55 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Thanks Trav..

I think I will run a bottle of techron, go burn some mileage on the highway, and get the O2 sensors on order, and go from there.

James: I just replaced the spark plugs with OEM Iridiums at 100k and also cleaned the TB at that time.
_________________________
'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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#2560753 - 03/08/12 02:07 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
ltslimjim Offline


Registered: 08/06/10
Posts: 5143
Loc: PL&F
^As a note, the longer a PEA containing fuel system cleaner can remain in the gas tank the better. It isn't a stripping solvent but a detergent that is best used on a full tank that you will use over a longer during of time.
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#2566212 - 03/13/12 11:40 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Update:

I took the car out for a nice drive this past weekend with lots of high RPM miles to heat things up. Then as luck would have it, got a flat tire (sidewall) and interrupted my work. Anyhow, I replaced both O2 sensors, and reset the ECU. I also cleaned the MAF and cleared the codes. We will see what happens. I *did* notice the exhaust had a different smell when letting the car idle. Before the sensor changes, the exhaust smelled in excess of fuel. Now, not so much, so hopefully things are better! If not, I suppose a cat replacement is in order!
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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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#2566226 - 03/13/12 11:59 AM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
MysticGold04 Offline


Registered: 01/12/05
Posts: 1133
Loc: CA
Sidebar on the Flat: I jacked the car up and put the spare on.. and continued working on the planned o2 sensor changes on Sunday. Yesterday I took the car and tire to Americas Tire since I bought the tires (and replacement certs) from them. They ended up replacing the tire for free, so I just had to pay the CA environmental tax, and a new certificate. I also opted to purchase a second new tire to have a "matched" set of tread since the other tires are at about 4-5 32nds of tread left. I hope I'm done spending money on this car for awhile, but it is the wife's car... It is comfortable, safe and is relatively inexpensive to drive - less than a new car payment every month, and safe for her and the kids to run around in.
_________________________
'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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#3228625 - 12/26/13 07:40 PM Re: P0420 Code... CAT or O2 sensors? [Re: MysticGold04]
mitmaks Offline


Registered: 10/09/11
Posts: 13
Loc: WA
I was wondering if replacing o2 sensors fixed your issue?

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