4Runner4Christ

Matt, It will keep coming back, I'll guarantee it. I do not know anything about the oxygen capture test. A Google search shows nothing. I assume a knowledgeable exhaust shop will know...

MTL_4runner

I read through all the posts and I'll make a few comments to help get everyone on the same page. First when talking about oxygen sensors, there is only one bank (ie Bank 1 as opposed to Bank 1 & 2 you you might see on other vehicles with (4) O2 sensors) on a 3.4L 4runner or Tacoma. On Bank 1, there are 2 sensors (surprizingly, they are named Sensor 1 and Sensor 2). Sensor 1 is responsible for closing the feedback loop for the ECU to control fuel flow to the engine (ie tells the ECU if the engine is too rich/lean at a given point in time and how far to adjust). The Sensor 2 is solely used by the ECU to tell if the converters are properly converting the various byproducts of combustion (unburned fuel, NOx, carbon monoxide, etc) into more environmentally friendly components (nitrogen, carbon dioxide, water, etc). The issue here is that your dealer is actually correct, because there are only (2) O2 sensors and 2 converters between them, it would be impossible to deduce which one(s) are faulty by using the O2 signal alone (like you could on a single converter truck....ie non-CA spec vehicles). There are a few tests that can be done to find which of the two are faulty (if not both) but it could be quite expensive and time consuming.

When replacing the converters you need to be a little more picky with the CA spec vehicles because I believe (not 100% sure, but the evidence is leading us that way) that they might have more stringent specs built into the ECU which specify the acceptable levels of byproducts present at the second O2 sensor. On CA vehicles you need to make sure that the replacement converters are 3-way AND CA approved (more than likely being CA approved means they are also 3-way, but verify first!). Also if you had 2 converters, don't go back to one or you may continue to get a CEL....replace each converter that came on your vehicle with another unit.

Here is a great link to help explain converters and how they are tested (not all inclusive though):
http://www.autoshop101.com/forms/h64.pdf

ironroad9c1

dude ,i will garuntee its a bad O2 sensor ,can't believe no one brought that up ..change the one behind the cat.bet that cures it..

MTL_4runner

It could be a bad O2 sensor that causes this condition (and actually the front or rear sensor could be causing this issue....more often than not it is more likely the front sensor than the rear), you are correct, but it is also a definate possibility that there is a leak in the exhaust or that the converter(s) have gone bad as well . There is a procedure for diagnosing these codes and it will take you through step by step (issue is that many of these tests need to be done by a shop or you just have to pay up and play parts replacement), see the FSM link below:

Code P0420 procedure:
http://www.deserted1.com/FSM/Repair_...fe/cip0420.pdf

A/F sensor diagnostic:
http://www.deserted1.com/FSM/Repair_.../afrs/insp.pdf
http://www.deserted1.com/FSM/Repair_...e/cip21952.pdf

Oxygen sensor diagnostic:
http://www.deserted1.com/FSM/Repair_...e/hos/insp.pdf
http://www.deserted1.com/FSM/Repair_...fe/cip0136.pdf

You can see how it's probably easier to just replace the parts. I do agree on it being a good call to look at replacing the A/F and O2 sensors before changing the converter. It may not fix the P0420 code but it should at least prevent future damage to the converter (and may have contributed to your current situation).

LSUMatt1514

One of the steps on the decision tree (P0420) is to check for exhaust leaks. I had a substantial leak at the inlet to the muffler, both at the top and the bottom of the inlet. Could this have been the root cause all along?

My thoughts are this. The leak was there, but hadn't gotten severe enough for me to hear it. Then one day last week, it decided to open on up and I noticed a substantial change in the sound of my exhaust on take off. Upon further inspection, I found the aluminum of the muffler basically peeled back on the top and bottom of the inlet pipe. This issue with the cat has been going on for a while but again, the leak was probably there and I just hadn't noticed it because it hadn't gotten bad enough to change the exhaust tone.

I mentioned this earlier in the thread. I was thinking that maybe the leak had allowed some air in leakage into the exhaust stream that somehow back-flowed to the rear O2 sensor, thus making it think that the cats weren't doing their jobs. Just a hunch...

I haven't gotten the code since I cleared it the other day. For now, I'm gonna bide my time and see if it comes back before I spend any money on testing or replacement parts.

Great post by the way!!!

Matt

MTL_4runner

Matt, the exhaust leak usually needs to be between the engine and the converters to be able to cause damage to the catalyst so I don't think a muffler leak would be the culprit here.

LSUMatt1514

I figured it wouldn't, but it was worth a try. I'm just not going to go out and spend $1,400+ on a stock system right now. I haven't noticed any decrease in performance, so it's obviously not plugged up. If anything, I've got better performance (specifically throttle response) after I had that new muffler put on the other day. I'm gonna bide my time and see what happens. It just sucks that we're stuck in this situation to begin with...

Matt

4Runner4Christ

Replacing the sensors did not fix this issue for me. I replaced both sensors and the problem resurfaced after 1.5 years.

LSUMatt1514

4Runner4Christ,
You nailed it. It came back on today on the way to Lowe's. Glad I bought the OBD2. I cleared it and went on my way. This is the quickest that it has ever resurfaced however. Usually it's a few months before it comes back. I cannot afford to drop $1,400+ right now on this. Nevermind the fact that I won't do it, my wife would kill me if I did!!! Oh well, guess I'm gonna have to get used to this.

Matt

LSUMatt1514

Here's the temperatures on the exhaust pipe that I measured this morning after driving an hour to work...

Before 1st O2 sensor--445
Before 1st Cat--395
Between Cats (Right before the 2nd one)--285
After 2nd Cat--265
After 2nd O2 Sensor--295

I double checked the reading after the 2nd O2 sensor, and it continually read higher than the outlet of the 2nd cat. I don't understand this. These numbers mean anything to you guys? Do they point to anything specific? Thanks.

Matt

LSUMatt1514

I did use an infrared thermometer so the readings should be accurate. I checked each several times. They bounced around a little, but the numbers above are pretty darn close. I still don't understand that increase in temp after the second O2 sensor.

Matt

LSUMatt1514

I'm going to talk with the service manager here in Birmingham at Limbaugh Toyota tomorrow and give him these temp readings and see what he says. I think that reading after the rear O2 sensor has to be erroneous. He's knows me quite well and I trust him, so maybe he'll have some input after hearing these temperatures. I'm also thinking about going to a Meineke or Midas and have them do a pressure test to see if the catalyst is plugged. I don't think this is the case because I have not noticed any decreases in power, lagging, etc. If anyone else has any input, please chime in. Any chances it's that rear O2 sensor that is bad? If that's the case, wouldn't it throw a code to the ECU that it was bad and not that the catalyst efficiency was bad? Thanks.

Matt

LSUMatt1514

If this is true, then maybe both of my cats are bad....

"Just because a converter is passing gas doesn't mean it is okay. If the catalyst inside is contaminated or worn out, high carbon monoxide (CO) and/or hydrocarbon (HC) readings will be present in the exhaust. If you have access to a high temperature digital pyrometer (or an oven thermometer will do), check the converter's temperature fore and aft. A good converter will usually run 100 degrees F hotter at its outlet than its inlet. Little or no temperature change would indicate low efficiency, or a problem with the converter's air supply. Converters need supplemental oxygen in the exhaust to reburn pollutants, so if the air injection system or aspirator valve isn't doing its job the converter can't do its job either."

Found this here...

http://autos.yahoo.com/maintain/repa...ques083_0.html

MTL_4runner

Matt, the change in temp on the older 2-way converters would be 100 degrees (usually due to having air injection), a 3-way which 99% of all vehicles use today would have about a 20-30 degree higher outlet temp than the inlet. When you are meauring these temps make sure you are hitting the actual converter (you want temps litteraly right before and right after the catalyst, but still on the converter) and not the pipe since the temps are so extreme and the heat can be lost very quickly over a short distance (also note your ratio on the gun you're using....8:1, 12:1, etc.....to make sure you are close enough to just be getting what you want to read and not surrounding temps.....ie the closer the gun is held, the more accurate the temps will be). Also be sure to try and get readings at around 2-3k RPM (obviously you'll need a helper) because idle may not flow enough to activate the converter much and cause the temp inlet/outlet change.

Here's a better article for you since the other sounds a bit dated:
http://www.findarticles.com/p/articl...23/ai_n8567589

LSUMatt1514

Thanks MTL!!!

Matt

LSUMatt1514

Guys,
I don't know what has changed, but this things is throwing the CEL every 3-4 days now instead of every 3-4 months. Something has obviously changed for it to be throwing it out so much more frequently. I mean I did have my muffler replaced, but that should have nothing to do with it at all. I'm started to get a little worried because again, I can't drop $1,400+ for a couple of cats right now.

Matt

jimbob

Just a thought, if the cels started (or became more frequent) after the muffler replacement, could it be the freeflow nature of the muffler is screwing with the cat operation?

Less back pressure >>> higher flow >>> less residence time of the gases on the cats >>> incomplete reduction >>> O2 sensor reports. You might just be fighting physics? Or it could be telling you the catalyst is poisoned.

Just conjecture.

BOSTON4RUNNER

I had the same code,,,,but I have one cat

i have a bad smell at the rear of the truck, not quite eggy but smelly, bad

so I replaced the 02 after the cat, tuned it etc, truck runs great....but code went off again

I did have the Evap go about a year ago and I let it run with a bad Evap for a long time, I am thinking, be willing to bet it is my cat, that it is clogged, messed up, full of crap,,,

So Friday, I am going to my friends shop, cutting out the whole exhaust, putting in a new high flow cat, a flowmaster 2.5 inch 50 series muffler, all new 2.5 inch pipe

Good luck with your issue, I am betting a cat, or cats have failed, at this point I am fairly certain that is what it is on my truck

LSUMatt1514

BOSTON4RUNNER,
How many miles do you have on your truck? I'm at 156,500 and starting to think that it's just old age that has caused it to die. I don't know if me manually clearing the codes is causing it to become more frequent, but I cleared it this morning after it popped up on the way home from work yesterday morning and guess what....I just got home and it came on again on the ride home.

It's not the muffler because I've had the same Dynomax on there for years. It was replaced under warranty because it split open on the inlet pipe. That can't be it.

The problem is, I don't know which one is bad or if both or bad? I don't know if some other problem caused one or both cats to die or if they died from old age? It's a catch 22 at this point.

I'd love to just cut out the rear cat, install a Magnaflow and be done with it but I seem to recall reading that others have done that only to have the light come back on on them because of the tuning of the rear O2 sensor not working with the high flow cat. Plus, I don't know for sure if it's my front, rear or both that are bad.

I haven't noticed any performance degradation, but it is really getting on my nerves and would like to do something about it, but I don't know what. It seems like folks are having this issue on the forum, but noone has come up with a definitive solution and/or root cause for the problem yet. I found a website the other day (of course I can't find it now) that specifically said if your car or truck has over 150,000 miles that it could be dead from old age. I haven't noticed any bad smell or lack of performance, so has it just died on me and it's not performing as efficient as it should?

Where do we go from here......

Matt

LSUMatt1514

Would it be worth the effort, money, and time to go to a Meineke and have them check it out or a total waste of effor, money, and time? I've got a feeling it would be the later of the two.

Matt