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Ex-Master Diagnostic tech
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I recently ran into this with my brothers Sienna. Code P0420 was present. I tested the converters and it appeared they were bad. I then checked the tech info center at www.techinfo.toyota.com and ran across a TSB on this . ECM replacement was required. I replaced the ECM a week ago and 2 days later she passed inspection. No mil so far and it runs better with more power and the mileage is slightly up as well.
I wanted to pass this along.
 

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I'm getting this code on a 2001 Sienna - P0420, catalyst efficiency below threshold bank 1. How do you test the cat converter? This vehicle passed emissions inspection not too long ago. Van has 132,xxx miles on it. Should I maybe replace the O2 sensor? Btw, I also had the VSC and trac off lights on as well. Any advice is appreciated.
 

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The cars emissions trouble-shooting system has no way to directly test the CAT for efficiency and thus report that it IS the problem. The system checks CAT performance indirectly.

P0420 usually means there is a problem with the 02 (A/F) sensors, their circuits (wiring) or the CAT. The exhaust system has 02 (A/F) sensors before and after the CAT. The signal outputs from the two sensors are compared by the ECU to determine the efficiency of the CAT.

If the signals are of the same amplitude, the ECU triggers the code. Meaning there is a problem with either of the sensors, their wiring or the CAT is operating below efficiency. There are specific trouble codes for the sensors but none to indicate the CAT is bad.

If no other codes are indicated pointing to a 02 (A/F) sensor then running down the problem is harder without doing some kind of diagnostics. The Toyota dealer or any shop equipped with the right type of equipment can determine if it is a sensor or CAT problem without guessing.

The VSC and TRAC system will turn off any time the CEL light comes on to minimize engine load. Fix the P0420 code and the lights should go off.
 

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My P1135, P0420 Problems

For anyone having issues with the P0420 code, seeming to indicate a bad catalyst, here's my story. 2002 Sienna, 128,000 miles.

In October, got P1135 code. Replaced bank 1, sensor 1 (needed to take to exhaust shop after stripping threads--they welded in a new threaded bung for $100).

A week later I got code P0420. Using my OBD reader, I found my Bank 1, sensor 2 voltage jumping up and down, rapidly, seeming to indicate a bad catalytic converter. My Bank 1, Sensor 1, and Bank 2, Sensor 1 resistances were good.

For fun, I replaced Bank 2, Sensor 1, since it is so easy to get at. Immediately after starting my engine, a light plume of white smoke came from the tailpipe for about 20 seconds. That'd never happened before!

My Bank 1, sensor 2 voltage no longer oscillated as fast or as much, indicating better catalytic converter function. I cleared my P0420 code, and it has not reappeared in several hundred miles of driving, and my readiness monitors are "ready."

So, if you get a P0420 on a Sienna, I'd recommend replacing both A/F sensors. You can get Denso models for about $140 if you look, online.

~Pete

Addendum: About 3 months and 15,000 miles later, my MIL came on with P0420 again. It was transient, and the code cleared within a couple of trips...hopefully a fluke!
 

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Clarify please.

I have a 2002 Sienna with the same problems after I replaced Bank 1, Sensor 1. Check engine light disappeared for a little while and then came back with the P0420 code and saw your posting.

Could you clarify the sensors you replaced. I got a little turned around in your explanation. I highlighted the sensors in question. It may seem you typed something other than what you were thinking? Thanks.

-Mao

A week later I got code P0420. Using my OBD reader, I found my Bank 1, sensor 2 voltage jumping up and down, rapidly, seeming to indicate a bad catalytic converter. My Bank 2, sensor 1, and bank 2, sensor 1 resistances were good.

For fun, I replaced bank 2, sensor 1, since it is so easy to do. Immediately after starting my engine, a light plume of white smoke came from the tailpipe for about 20 seconds. That'd never happened before.

My Bank 1, sensor 2 voltages now no longer oscillated as fast or as much, indicating better catalytic converter function. I cleared my P0420 code, and it has not reappeared in several hundred miles of driving, and my readiness monitors are "ready."

So, if you get a P0420 on a Sienna, I'd recommend replacing both A/F sensors. You can get Denso models for about $140 if you look, online.

~Pete
 

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I have a 2002 Toyota Sienna. At 79910 miles the check engine light came on.
My scan tool came up with the following trouble codes:
* P0420
* P0420 P

I took it to the Toyota dealer, who said the problem could be:
* Oxygen Sensors (about $150 each, X2)
* Catalytic converters ($1700)

My brother thought it might be bad gas (or the 10% ethanol in the gas) causing problems, so I added "Lucas Oil Deep Clean Fuel System Cleaner" to a full tank of gas and reset the check engine light.

The van ran great and the check engine light stayed off for 310+ miles.
With less than a 1/4 tank of gas, I refilled van with gas at HESS. Drove for 152.7 miles, then the check engine light came back on.

Used my scan tool to reset the check engine light at 80450 miles to see if it comes back on in 310 miles again or sooner.

Questions:
What could be causing the problem?
A bad sensors I could understand, but I always thought a catalytic converter should last longer than 80K?

Any advice would be greatly appreciated.

Thanks!
 

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Unfortunately, I doubt it's the gasoline.

Did you get your van to the dealer before the 8/80,000 emissions warranty expired? If so, you might be best served pursuing a fix under the warranty.

You're correct that a converter should last much longer. But, if an air/fuel-ratio sensor becomes faulty, it's conceivable this could cause the engine to run rich or lean, thereby reducing converter life.

So, there are several possible root causes of this code, including too strict logic in the ECU, and the fixes are expensive. You have the advantage of having your own scan tool, though, so if you're willing to try things yourself, you can start with the least expensive possibilities, like a leak in the exhaust system, and then the sensors.

Following up on my experience, I now live with the P0420 code much of the time. I'm able to get through emissions inspections by resetting my codes, then taking long highway trips, which don't set this code for me. My next option is to replace my oxygen sensor, Bank 1, Sensor 2, but this wouldn't be easy, due to rust where the sensor mounts. I suspect a bad sensor, due to its waveform pattern, which resembles "artifact" oscillation, but seems to confuse the ECU to setting P0420.

Good luck!
 

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Thanks pjksr02.

Yes... I looked up the info on the 8 year 80,000 mile emissions warranty before I took the van to the dealer in December at 79,910 miles, as I thought it would be covered under warranty.

Unfortunately the vehicle age is measured from date of first purchase which was March 2002, more than 8 years ago. I even called Toyota headquarters and got the same lousy answer. I explained to the Toyota rep that the van (purchased used at 25k) came with a "Toyota certified" warranty, but they said that was only good for 7 years, 70k, so I was out of luck.

While the van was at the dealer, they got the same trouble codes I did, but recommended replacing the catalytic converters.

Also... A few years ago around 62K, I got a trouble code indicating the air/fuel-ratio sensor was bad, so I had it replaced at the dealer, but they did not cover it under warranty either.

So... based on your suggestions I will check for exhaust system leaks, then try to find a way to test the sensors.

Questions:

1. From my experience resetting a check engine light is only a temporary fix as it will come back on after the vehicle is run for about 100 miles.
Why did the light stay off for over 300 miles after I used the Lucas Oil Deep Clean Fuel System Cleaner? I noticed the product says it helps to reduces emissions.

2. Could the 10% (or more) ethanol in todays gas not be burning correctly and causing more pollution which is causing the sensors to register a fault?

3. Could the Lucas fuel treatment be making the gas burn cleaner so the exhaust is now within the sensors specs?

Thanks again for your help!
 

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Side note...
Ethanol problems:

Also, doing a quick Google search on: ethanol damages engines I have learned that 10% Ethanol (E10) blended Gasoline:
* Has a shelf life of less than 3 months (in ideal conditions: no water, no humidity exposure)
* Absorbs water quickly
* Lowers MPG and HP (about 10%)
* Can damage plastic and rubber parts, hoses, fuel pumps, and engine gaskets.
* Engines older than 5 to 10 years, may not be compatible (unless re-designed to be compatible with E10)

Other info:
E10 Gas Precautions and Tips:
http://www.fuel-testers.com/ethanol_engine_precautions.html

The Great Ethanol Scam
http://www.businessweek.com/lifestyle/content/may2009/bw20090514_058678.htm

Pending lawsuit between the automakers and the gas companies over ethanol damaging cars:
http://www.thedetroitbureau.com/2010/12/automakers-sue-to-block-expanded-ethanol-usage/
 

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Bummer on the warranty!

The check-engine light will stay off until the ECU has tested the emissions system and gotten the P0420 condition on two successive tests. You have to fulfill requirements for the ECU to test the system, such as coolant temperature and vehicle speed. There is a part of the ECU logic that makes sure these pre-conditions are met, before testing for codes,and this is called the "readiness monitor." It's possible, especially in winter, to drive your van on short trips, and never even have the ECU test the catalyst system, say, if your vehicle doesn't warm up and you don't drive it long enough.

You may wish to go to siennachat.com I and others have posted there, too...

You won't hear me argue with ethanol being a possible cause of our woes. It could be possible, too, that a fuel system cleaner reduces emissions to below threshold; a cleaner might be a tool to help through an emissions test. For what it's worth, I run Redline SI-1 almost continuously. My 2002 Sienna has 160,000 miles.
 

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Thanks for the info!
I did not know the conditions for the ECU to test the system and that it could be effected by outside temperature. It's been bitter cold in NY, so maybe that's why it lasted so long?

What's the best way to get the check engine light to come back on? 2 long trips?

I will check out siennachat.com to see if they can help also.

As for fuel system additives, I noticed that Redline SI-raises the octane and Lucas Deep Clean "eliminates the need for high octane fuel." I wonder if both raise the octane just enough to make the engine run better and keep the check engine light off?
 

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My Hypothesis

I believe I have the P0420 thing figured out.

If you will notice when this code starts appearing you will have idling problems. This is due to the Electronic Idler Valve (EIV as I call it) on the back throttle body intake getting all gooped up. I believe the back intake valve goes into the rear three cylinders. When the EIV goes bad and loses range of movement (to open and shut the vacuum valve) it fouls up the A/F mixture in the rear three cylinders. This causes the A/F sensor at the rear cat header to go bad thus beginning the problem process. With the sensor bad, the cat will begin to clog and foul up. This causes less exhaust flow into the rear header and causes over-scavenging. Over-scavenging causes blowback into the inlet side of the butterfly valve thus fouling the EIV. This cycle repeats itself and gets worse. Thus people replace the EIV and find it getting gooped up again in a short amount of time.

My only question is which one of the three causes the beginning of the cycle?

Just my 2 cents! Feedback welcome!
 

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Here's a link to drive patterns:

http://www.toyotapart.com/READINESS_MONITOR_DRIVE_PATTERNS_T-EG02-003.pdf

In my van, taking long trips is the way I keep P0420 from recurring, after I clear my codes. When I am bopping around town, stopping and going, I can almost predict when the light will come on.

Not sure if Redline actually raises octane. I tend to think it reduces acquired octane requirement--increased octane needed due to deposit build-up--through cleaning.
 

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Thanks for the advice dictatormao.

Your hypothesis is very plausible and a good idea of something to check out.
Is the Electronic Idler Valve something that can be serviced by a home mechanic?
Also, would the van have engine / performance problems if this part was a bad?
The van runs great and has lots of torque. Even the gas millage is decent.


Thanks for the PDF pjksr02.

I understand that there is a software update for the van's computer.
Is this the "12 Megabyte Diagnostic Tester Program Card with version 9.0a Software" that I read about in the PDF?
Is it possible that just a software update would fix the P0420 problem?
Has anyone had this done? How much would the dealer charge to do this?

As for Redline... it says on their website that it "reduces need for octane by up to two points" whatever that means, but it sound like good stuff!

Thanks again!
 

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Wouldn't that be nice, to flash the ECU? Unfortunately, our ECU isn't flashable, so you have to buy a new one, with new logic, and a new part number. Even a new ECU doesn't guarantee a fix, because the catalytic converter(s) may still be bad. (See http://ww2.justanswer.com/uploads/snd27613/2008-10-27_103701_p0420.pdf ).

Hopefully, you're not due for an inspection soon. As long as P0420 is your only code, you don't have to worry about damaging your engine, so you can continue to learn, then try the cheap-fix ideas, before having to bite the bullet on a big repair. But, if you have an inspection coming up, and if it includes emissions, you will fail with the CEL on, and you will not pass unless your readiness monitors are mostly "ready."
 

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Yes, the van passed inspection 1 month before the problem started.

I did a search and apparently there is a way to Flash the ECU...
http://www.carcomplaints.com/Toyota/Sienna/2002/tsbs/

TSB #TSB-0064-10
NHTSA ID #10034284
Date Announced: FEBRUARY 04 2010
Additional Info: How to Fix
Summary: TOYOTA: TECHSTREAM ECU FLASH REPROGRAMMING PROCEDURE. FLASH REPROGRAMMING ALLOWS THE ECU SOFTWARE TO BE UPDATED WITHOUT REPLACING THE ECU. FLASH CALIBRATION UPDATES FOR SPECIFIC VEHICLE MODELS/ECUS ARE RELEASED AS FIELD-FIX.


Question:
Even though the van has P0420 and P0420P (Oxygen sensor before cat and after cat, with Catalyst System Efficiency Below Threshold (Bank 1)." is it OK to keep driving it?
I don't notice any performance problems.
Will driving with the problem damage the catalytic converter or other engine components?

Thanks!
 

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If you can actually bring up that TSB, you'll find that our year's ECU isn't flash-capable. I'd love you to prove me wrong though!

Someone else can chime in here about the P0420, but I'll reiterate my view there's no danger of engine damage. The downstream sensor's output solely monitors catalyst efficiency, and does not input into engine operational parameters.
 

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Hmmm... I cannot find any more info on that TBS.

Based on the advice I've read so far, I checked the exhaust system for damage, holes and gasket leaks but found none.

However, I did noticed that the oxygen sensor *after* the catalytic converter had been replaced (must have been 5 years ago when I bought it) and who ever did the repair snapped the rusted bolts off, but used an orange adhesive to glue the replacement sensor in place.
I showed this to my friend who is a maintenance mechanic and he said it is a standard high temperature silicone adhesive that is safe to use for sensors and while not the best repair, it looks solid.

Also...
I checked all the vacuum hoses for damage or loose hoses and found none.
I looked for the Electronic Idler Valve you mentioned, but could not find it.

So, there is no danger of engine or catalytic converter damage with a P0420 and P0420P trouble code?

Thanks again for all your help!
 

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<<< CORRECTION >>>

The oxygen sensor that has the high temp adhesive holding it in place is AFTER the LARGE Catalytic Converter under the middle of the van (Bank 1, Sensor 3).

The sensors for Bank 1 near the engine (closest to firewall) look like the originals. However, I can't figure out how to remove them as there is no room to work with all the other parts in the way.

Questions:
* How do I remove these oxygen sensors?
* Is there a special tool needed to reach them?
* Is there a way to test these sensors?
and just to confirm...
* Is there any danger of engine or catalytic converter damage to continue driving with the P0420 and P0420P trouble codes?


Thanks again!
 

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First, "will this cause further damage?"
If you are getting codes your engine is not operating correctly. In most cases it will be running rich. Some say this will damage a cat. You need to fix the problem and there is a solution. We need to figure it out together. I've never had these problems with my 220,000 mile Sienna so it's not like it's a design flaw or something. I have noticed that most of the poster's here have 2002 or 2003. Are all of the poster's driving VVTi motors?

Anyway there are three sensors total. Two are mounted high in the manifold and the third is mounted after all of the cats. It's plug actually connects inside the van under the passenger seat. The front sensor (bank 2) is obviously easy to get to. The rear sensor (bank 1) is difficult to get to. When I change mine, which I've done twice over the years, it's a real fight. The last time I out smarted it and had my daughter plug the connectors in. Unplugging it and re-plugging is the most difficult part. I think that I used an O2 sensor socket but I may have used an open wrench. I think that either will get in there. I think I used a huge standard wrench. You can test size on the front one. The rear one must be removed from underneath the van. Space is very tight but it can be done without taking anything apart. The first time it took me over an hour but I knew I'd saved lots so I didn't care. When I enlisted my 12 year old daughter I got it done in 15 minutes.

The sensors can be tested once removed. This is basically a cat thread but there is another thread about O2 sensor codes that has all of the O2 sensor info.
 
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