Are you in an area that requires emissions testing? And if so, do they just check for check-engine lights ... or use a tail pipe sniffer?

The following would not work if they use a tailpipe sniffer. Tailpipe emissions are unchanged, but we don't have emissions testing around here. Obviously, this fix is not recommended if the CATS are physically damaged or corroded either.

I just had this problem on my 2004 Sienna, but I had BOTH P0420 and P0430 ... so BOTH my CATS were bad. I couldn't afford to have both replaced ... so I used the Radio Shack diode fix.

Rather than replace the CATS, I soldered a standard Diode from radio shack (P/N: 276-1141) into the sensor lead (blue wire on a Denso O2 Sensor) of each downstream Oxygen sensor (silver diode marking must be towards 02 connector/ECU).

I've done this on a couple of Pontiac Vibes (really a Toyota Matrix) with the P0420 ... and it works! ... the light goes out. The diode reduces the voltage sent to the ECU, which "fools" the ECU into thinking the CAT is working fine. The downstream O2 sensors don't control or affect engine management ... they simply monitor the CAT efficiency.

I've put about 1000 miles on my Sienna, and about 7000 miles on my Pontiac Vibe GT ... and the Cat codes have not returned.

 

...

Rather than replace the CATS, I soldered a standard Diode from radio shack (P/N: 276-1141) into the sensor lead (blue wire on a Denso O2 Sensor) of each downstream Oxygen sensor (silver diode marking must be towards 02 connector/ECU).

I've done this on a couple of Pontiac Vibes (really a Toyota Matrix) with the P0420 ... and it works! ... the light goes out. The diode reduces the voltage sent to the ECU, which "fools" the ECU into thinking the CAT is working fine. The downstream O2 sensors don't control or affect engine management ... they simply monitor the CAT efficiency.

Geoffzie, do you happen to know the amperage through the O2 sensor? wouldn't a simple resister be enough to reduce the voltage reaching ECU?

 

Interesting idea...
Before I was able to find a new ECU, I was considering options to minimize the final O2 sensor input. However, the anti-fouler method would not work on the bolt-on style of O2 sensor that the 2001 Sienna has. Fortunately, it only has 1 post cat sensor.
I think I will try my original cats first. If that doesn't work, I will give your idea a try. I have the original O2 sensor too, so I could modify the single wire on it for a quick test.

 

Does the downstream o2 sensor affect fuel efficiency? Thx

 

My understanding is that the downstream O2 sensor doesn't affect fuel efficiency, it only checks to see if there is a drop in emissions after the cat compared to before it.

I still get a P0420 code about once a month and would not have been able to stand keeping the vehicle had I not installed a switch on the check engine light.

Post #19 here: http://www.siennachat.com/forum/62-...-maintenance-repair/22745-rear-valve-cover-gasket-replacment-2000-sienna-2.html shows what I did. That way you can turn it off when it comes on and then check it when you get home. It's not safe to drive around staring at that stupid light.

 

Kocoman no, the downstream 02 sensor does only one thing ... like iRt said, it only checks for CAT efficiency.

And like RobertB said, the Gen. 1 Sienna's had only 1 downstream 02 sensor ... the Gen. 2 (2004 and later) have 2 downstream 02 sensors. So on 2004 and later, when the CAT isn't working, you'll get a P0420 for the REAR bank ... and a P0430 for the FRONT bank. (the lower number code is always the bank where number 1 cylinder is located).

The thing I like about the diode method is ... you still have a workable check-engine light. Which is valuable since you can instantly see when there's another problem.

RobertB ... yes I've tried the spark plug defouler method too (available at Advance Auto Parts), and it works equally as well ... providing your downstream 02 is the screw-in type.

The way I understand it, the downstream 02 sensor measures emissions AFTER the CAT ... and sends a voltage signal to the ECU, and compares it with the voltage signal of the upstream 02 sensor (or Air/Fuel sensor on 2003 and later Sienna's).

That voltage signal of the downstream sensor, when the CAT is working correctly, should be considerably less than the upstream sensor. If the voltages are nearly the same ... it means the CAT isn't working ... and the check-engine light comes on.

The Radio Shack diode simply reduces the voltage signal being sent to the ECU ... permanently!

Just make sure if you use the diode method, that you seal up the wires good with shrink wrap tubing or electrical tape. On my Pontiac Vibes, the splice ended up INSIDE the car under the carpet, so water wasn't a problem. That isn't the case with the Sienna.

 

Hi Robert. Did I miss that you replaced the original downstream oxygen sensor? If you have not, then that sensor is likely sluggish, and could be causing the P0420.

 

Although I would think that if the O2 sensor were defective ... it should throw a code. I've never had much luck in eliminating a P0420/P0430 by simply replacing the downstream O2 sensor.

 

I replaced the O2 sensor 2 years ago when I first got a P0420 code. That was the cheapest thing to try first. After that, I replaced the main cat with a Walker cat. That briefly worked, but then the code returned in a few months. So I replaced the y-pipe with the Bosal pre-cat.(This pre-cat is really the important one for the ECUs cat test according to a Toyota tech) I still had the P0420 code. Finally, I found an updated 89661-08062 ECU at a local junkyard. I then reprogrammed the 93C56 chip to allow it to run in my 2001 Sienna. This cured my code for almost 2 years. So I think one of my aftermarket cats is "below threshold" for even my updated ECUs test now. You get what you pay for. Aftermarket cats are cheap for a reason....platinum and palladium are expensive.

If restoring my OEM cats does not clear the code, I may try splicing in a diode on my old O2 sensor(which I still have) for a test. I am hoping the OEM cats are good with the updated ECU.

Geoffzie,
O2 sensors can throw a code if the heater circuit fails. But if it has just become "lazy", it won't throw a code. Replacing it obviously did me no good either, but some people have solved their P0420 code by replacing it.

 

Robert, it could just be an intermittent code. If you clear it, you might not get it back for some time.

(My experience in my 2002 was that replacing my rear oxygen sensor solved my P0420, back in about 2010. The van threw the code once since, about two years ago; I cleared it and it hasn't come back, knock on wood/metal.)

 

My P0420 code kicked on Thursday after driving about 250 miles. It remained on after our 320 mile return trip on Friday. It has only been driven on short drives around town since. I will pull the code tonight and see if the code is still "pending." If it is pending, the most recent cat tests are still producing failures. If it is only set as "historical", then it has a chance of not returning if I clear it. Shouldn't the ECU clear the CEL when 2 successive tests pass?

On a side note...
During my June vacation, I got the CEL for P0171/P0174 codes. These were "too lean" codes. I found a cracked vacuum hose that goes from the intake boot to the front valve cover. When the CEL popped on, I expected these to be the codes, as the 171/174 only came on during a long drive. The hose split at the connection to the front valve cover. If you ever need this hose, most Toyota dealerships will want to sell you the whole intake boot too. That is what my dealer wanted to do. A lot of the older databases don't list the hose separately. However, there is a separate part number for it. It is part number #1226120030. It can be bought for $20 instead of $150 for the whole intake boot assembly.

Final note: 1226120030 is for 2001-2003 only, not 1998-2000

 

I installed my old stock y-pipe and rear cat today. I cleared the code and drove it for 30 minutes. So far, the cat test hasn't been run yet. I will just have to wait it out now. I did notice that there was leakage at the y-pipe gaskets on both connections to the exhaust manifolds. That could have been part of my problem.
Today I also put on a new right mirror. The old one was a cheap "Ebay" replacement years ago. It worked, but it was flimsy and bounced around a lot. The new Dorman replacement(heated 5-wire) is much more solid, and is a perfect fit. It was only $43.79 at RockAuto.com.
Tomorrow, I will put on new rotors and pads.

 

Let us know how you make out. Yikes, you're swapping out exhaust pipes like it's routine!

 

It only took about an hour to swap the pipes....minus a trip to two AutoZones to get the manifold flange gaskets. It seems I ordered the wrong ones from Rockauto. So far, the cat monitor has still not been run. My wife drives too short of a trip to work to always get it run. In the past, it often took a week to get it done. The Evap monitor has already passed however. I may just have to take it for a drive myself because I really want to get this done.

 

Still no cat test run on the van since changing back to original cats...
I dug up the "drive cycle" document the other day. I will have to try to replicate it late some night when there is little traffic. There are few places in town where you can drive 35-45MPH(fluctuating) for 16 minutes without stopping in normal traffic.
The document that describes the Readiness Monitor Drive Patterns for 96-02 Toyotas is EG003-02.

I did "get" the opportunity to replace my radiator over the weekend. I noticed a small puddle of coolant on the garage floor while my wife was gone with the van. I knew it was trouble. I smelled coolant when she returned. Inspection immediately showed coolant on the top seam of the radiator. It only took a few more seconds to see the 3" crack in the plastic at the top near the upper radiator hose. It was probably just one more drive away from catastrophic failure. My son(a tech) says this is a very common failure point on old Toyota/Lexus radiators. The plastic at the top gets incredibly brittle over time. My son says that even a small accidental tap with a socket on it can crack it when they are old.

I was already tired from doing sheetrock repair(water pipe leak inside the house!) and mowing the yard...but I decided to tackle it right then. I knew I could get a good deal on the radiator and hoses from Rockauto, but it would be 4 more days until I would get the parts. So I went online and found the parts at a local Napa. I was lucky to catch a 20% sale that day! So the parts weren't too much more than Rockauto. It took my son and I only about an hour to swap it out. Bleeding the system after refilling it took longer. My son has a special filler at work that helps fill Toyota/Lexus radiators and "burp" the air out. But we didn't have one at home. Initially, we must have had a large air bubble in the lower hose. It just wouldn't pass any hot coolant. So we removed it from the block and after a moment it started to dump coolant. We then quickly re-attached it. I think this eliminated the major air pocket. After that, the hose would pressurize and pass hot coolant. After the engine cooled we noticed that it had drawn some coolant back in from the overflow tank. Mission accomplished. My other son's old BMW 325i had an air bleed valve on the thermostat housing. I wish our vans had one somewhere.

 

Good job with the radiator--glad you didn't find out somewhere far from home, in the middle of the night.

In addition to the drive patterns you mentioned, I have had my monitor tests run during highway trips. One trip I often make with a "run" is 95 miles on the highway. Keep driving it, I guess.

 

My monitors finally passed! I cleared all codes after I replaced the OCVs two weeks ago. I am surprised that cat test passed so quickly this time when it wouldn't pass for many months! Maybe there was a connection to a failing OCV?

But wait...there's always a catch...
I now have a P0446 code pending! It hasn't kicked on the CEL yet. No other evap codes like P0440 or P0441 are set. I did some research last night on the P0446 code. It seems that a lot of people have fixed this by replacing either the canister or the Canister Closed VSV(vacuum switching valve). One person actually took apart the valve and freed up the mechanism to make it work again. The VSV valve is actually attached to the canister and comes with the assembly. In theory, you can't even buy the VSV separately... at least from Toyota.

I scanned the net looking to see what the cost for the canister would be.(should I need it) New OEM Toyota canisters can be bought be a little over $300. The Dorman canister can be bought for under $200. So if I need one I may try the Dorman part. I replaced my canister 8-10 years ago once already.

But when scanning Rockauto.com, I noticed something very interesting...
There is a Dorman part(#911601) for a VSV valve. A note for this part on the website says "Mounted at Charcoal Canister." The picture of the part looks like the correct configuration. So maybe we now have an option to replace this valve instead of buying a whole canister. It's only about $24.

But before I start throwing parts at it, I need to check all my evap vacuum lines. I unplugged and replugged several when I was replacing the OCV valves and cleaning their filters. It's possible that one is leaking or cracked now after I disturbed the connections. The hoses are getting old and hard and they may not be properly resealing. We also recently replaced the starter (in the same vicinity) and removed some hoses to do that.

 

Always something, huh?

Let us know how you make out--I'd tend to suspect something other than the canister, since you already replaced yours. Did you use a Toyota canister as a replacement?

 

Yes it is always something. Especially over the last 12 months for me. I have about 149K miles on the van right now, so it has hit the point where a lot seldom replaced parts have failed at once. It seems that a lot of cars have to go through a round of this somewhere between 100K and 150K miles. (a mid-life crisis?)

I replaced the canister with an OEM Toyota canister. The "new" one probably has gone as many miles now as the original one. But since I was messing with evap hoses, it is quite possible(even likely) that this is not just a coincidence. The only thing that points to an independent failure is that my evap monitor is set to ready. Apparently, it passed once(at least) already in the last 2 weeks. This probably occurred before the pending P0446 code was set, as the test should fail if it generates a P0446. It's possible that I made a tiny crack in a hose that expanded later. If my pending P0446 kicks on the CEL, I will know that the problem is ongoing, and not just a transient failure.

So when I get a chance, I will recheck all of the vacuum lines I worked around. I will check the connections with a little carb cleaner to see if I can spot an obvious leak. Then I will reseal them with a little grease and verify the clamp it tight on the hose. If I can't identify a problem, it might be best to just replace all the evap vacuum hoses where I was working. I suppose I could easily check the VSV valve on the canister and the one on the back of the airbox to make sure that they click when voltage is applied. My son took out the airbox a month ago when he did the starter.

 

Hmm...
My pending P0446 code has disappeared! Good riddance!
I rechecked and repositioned some vacuum hose clamps.
I also tightened the gas cap.
Maybe one of those things did the trick.

I'll scan it every week and see if it shows up randomly.
If so, it could indicate an intermittent or marginal problem brewing.

 

what do you all think of "cleaning" the catalytic converter, like in this video https://youtu.be/5icTmYItwiE? a friend of mine did it to both of his cars with 195k and 175k miles on them, and it worked for both. the comments in the video also indicate that people who have tried it have had the engine code clearing.

 

Scotty KillMyCar makes LOTS OF MONEY on YouTube by giving gimmicky and poorly thought through but well marketed advice . Think about it. Would you want a mechanic to rev the engine that high and burn rubber when test driving your car? Does this guy even own a real repair shop? All of his videos seem to be made in his home driveway. But at the same time, he have you ever seen advertisements play before or during his videos? He hears, "cha-ching" every time. And laughs at people who comment that his "fix" broke their car.

That's not to say that all YouTube video advice is bad. It's only bad if the person is making a lot of money by giving wrong advice.

The inside of a catalytic converter operates at temperatures in excess of 1200 degrees F. The more unburnt fuel the hotter it gets, burning off anything that the lacquer thinner might clean out. If you let the exhaust system get up to temperature, that is. Driving just a few miles at a time won't do the trick. Short trips make everything wear out faster...

At least on a Gen 1, cleaning two of the three catalytic converters "off the car" requires unbolting the Y pipe from the manifolds. Chances of stripping or breaking a bolt when doing this is high. If the flex pipe has seen better days it may be damaged during surgery and require replacement. And no, I wasn't following KillMyCar's advice when I learned these things. My flex pipe had ripped away from the Y pipe because the last person to work on the exhaust took a short cut and didn't replace the hanger that supports the rear cat.

Your opinions, methods, and mileage may vary.

Sent from my Nexus 7 using Tapatalk

 

Well, I got the Revenge of the Revenge of the P0420 code...


So I ordered the Radio Shack diode as specified by Geoffzie and installed it today.
I'll post a follow-up in a few days/weeks when I get the cat monitor to run.

 

For posterity's sake, the diode referred to is a 3A 50V diode.

Good explanation of why this works and a resistor won't (scroll down to May 16 post): https://forum.miata.net/vb/archive/index.php/t-419162.html

Also note (obviously) that if you are somewhere that tests tailpipe emissions, you may not pass.

-Mike

Sent from my SM-G950U using Tapatalk

 

Thanks for following up on this.

I'm still of the mind that the hardware, the converters, are good, but the sensors and software throw codes.

I'm still on the original cats, with both A/F and the O2 sensor replaced, at 235,000 miles.

 

Well my cat monitor has passed. So far no codes too. I am still waiting for the Evap monitor to pass. However, that one seems especially unpredictable to get to run. My wife drives only about a 15-20 minutes each way to work.

Originally, a few weeks ago, my CEL popped on with P0171 and P0174 codes(too lean Bank 1 and Bank2) in addition to the P0420. I cleaned the MAF, and so far I get no more "too lean" codes. Because it was lean on both sides of the engine, it might be the MAF or a vacuum leak. I bought some vacuum line at O'Reilly's to replace the original old vacuum lines. But it was not snug enough. So I had to order vacuum line from Toyota to make sure I get the exact tight fit. They don't carry vacuum line in stock! It's been a week since I ordered it, and so far it hasn't arrived. How do they ever fix vacuum leaks in their shop? God forbid...

 

@Geoffzie I would like to say that you are an absolute saint. I have had a P0420 problem on my 2004 sienna for a year now. The problem is that the CATs are still mostly good, so it was hard to chase down the problem because the downstream O2 sensors showed generally valid data. I Checked for air/vacuum leaks, swapped downstream sensors, sprayed sea foam in the cats, used cataclean, changed spark plugs, added non-foulers to the O2 sensors, replaced PCV! You name it I've probably tried it. The diode trick was the ONLY thing that worked for me. My next sad step would have been to replace the CATS. I really like this diode trick because you can hide it from California emissions tests. CA testing sites (depending on how anal they are) will fail you if they see the non-foulers on the oxygen sensors. The diode is so much easier to hide! Thank you so much for that post you saved me hundreds of dollars.