P0420 Code... CAT or O2 sensors?

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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.
 
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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...
 
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.
 
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.
 
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.
 
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.
 
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
 
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.
cheers3.gif
 
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.
 
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
 
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.
 
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.
 
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.
 
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.
 
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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