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2000 Avalon P0420

6K views 17 replies 8 participants last post by  kaytea58 
#1 ·
Hi All,

I've read a lot on this forum about other member's issues with the P0420, so I'm familiar with a few of the things to check. But now I need advice.

My daughter bought the car recently from our mechanic.....he put a Lexus engine (92,000 mi) in to this 2000 Avalon (167,000 miles) because the previous owner drove without antifreeze and blew the head gasket. Also, new radiator and fan switch, and air filter. The new used engine came with the manifold converter and the mechanic put in 2 new A/F sensors.

The P0420 code came up after 2 weeks of ownership and he inspected for exhaust leak, etc. We've been back to him every week for him to check something else that might cause the code. Also on Live Data with the code reader, the ECT (coolant temp) varies between 183 (highway speeds) to 194 (stop and go traffic) which he originally said was low and changed a coolant sensor, but the temps didn't change, and now says those temps are ok. He said today that he thinks it's the catalytic converter (but not the manifold one) is bad, but he says just erase the codes as they come up for now.

I'm the Mom so I don't work on cars and have to rely on mechanics. Is there a way to check which catalytic converter is bad....I asked about the temperature test (seen on you tube) and he said the temperature test was fine but doesn't mean the converter is fine.

This car is a California standard (though we live in NJ). What should I do? get a second opinion? spend big bucks on a converter replacement (Daughter will have a fit since her previous used car was a total lemon and cost thousands in parts/labor--she doesn't want to go through this again). Is the coolant temperature an issue? There are only franchise exhaust shops near me so no nearby exhaust shops with stellar reviews.

The only good thing is she has 2 years before her NJ inspection sticker is due to renew. Any advice is appreciated!
 
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#2 ·
From what you say I don't trust the mechanic. It sounds like he cleared the P0420 code before selling the car then after a while the code will come back, I know because I've tried clearing the same code on my car. The code has to do with evap system and won't make much difference if the light is on, although if the roads are slick it may be problem because it may also turn off the VSC and TRAC. If you are not capable of diagnosing problems then the best thing is to call Toyota and ask how much it will cost to diagnose the code. The reason to use Toyota is that they have specific tools for finding problems with their cars. They can tell if if the coolant temp is correct as well.

GL. Nice to see a woman on board and not afraid to get involved.
 
#3 · (Edited)
Useless mechanic, probably trying to misdiagnose known ok items to rack up the bill to make it appear fixed. Don't worry pepboys and firestone do things like this as well; we have actual written problems found that do not come up again when checked by another person very next day/visit (magically fix themselves). Start with putting 1 seafoam or 1 cataclean in full gas tank for the 0420. Normally it would be better to put seafoam through vacuum (youtube it). Next get any codes read, stored or pending. If the engine bay is not clean, might be good to wash bay and under to check for any leaks or other issues.

Normal or preventative maint items. Not immediately. I think Lexus engine might have EGR (not sure) but it might need cleaning, along with TB, IAC, etc. Thermostat is good to be changed close to 100K ($20 oem + $100-150), esp on recently purchased car if unknown history. And with that you also get 1 drain-fill of coolant. ECT1 (coolant temp sensor) does not normally go bad that early. If your gauge is half way even in rush hour traffic then thermostat and sensor are most likely fine currently and you might not need immediate attention.

You can rent a scanner at autozone. If you keep it plugged in on a good driving day (using heavy streets or in rush hour freeway), you can see some good temp readings yourself. Youtube how to use obd2 scanner.

Things you can do in parking lot. Warm up the car and see if the radiator fans go on-off. Do Twice. Then turn on A/C low and see if fans come on. Put on high and see if fans come on again but higher or longer duration. If so, you are probably safe again immediately with or without using scanner. You can also gauge that against what your mechanic says ... Little checks like this and low cost items first helps save some money before any real fixes.

Maybe later in the week you can take it to a real Toyota dealer or mechanic. This you probably should do sometime after the light comes on again. Sometimes clearing 0420 takes few miles or days or weeks or months to come back if there is a evap problem (search P0420 in forum just to read up on it). This is not helpful in california if you are close to registration renewal time, if not, you have some time. I am in SoCal as well so I deal with in on the corolla sometimes.

As for catalytic converter, it should be around $150-300. Do some searches in the forum. Regardless, throwing money at parts still does not fix the root cause sometimes when dealing with bad mechanics or hard to find issues. Take it slow, if you are able to.
 
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#4 ·
Thanks, I was thinking we might have to take the car to Toyota for further diagnosis.

My mechanic is a good guy and we've taken 3 cars to him for 5 years...never had a reason to think he wasn't honorable. Before he replaced the engine he drove the car and told us that the P0420 came up but that he thought it was due to the overheating, not the cat. He contacted the former owner and was told that that code never came up before. Since he was confident it wasn't the cat, and that he replaced the manifold cat and 2 A/F sensors, I thought the car would be ok. After replacing the engine, he drove the car for a few days to make sure things were ok. On the day my daughter took possession of the car, I went with her to the MVC inspection station and it passed and she got her 2 yr window sticker. He did all the other followup checks and diagnostics of the car at no cost to us.

I don't suppose anyone's found an after market California cats that would be ok with the Toyota computer. Also, anyone know where can I find the correct ECT coolant temperature specs for this car?
 
#5 ·
Thanks, surgeon. Great suggestions.

I did Lucas fuel treatment injector cleaner in when the code first appeared. Also using better gas and did a tank with premium gas. No help. I also bought a code reader after the CEL came on for the second time. I drove around in the car in the Live Data mode to watch the coolant temperature, etc. I think I've watched almost everything on you tube about catalytic converters, including washing them in a bucket! :smile: Also putting a spark plug spacer at the downstream sensor.

I saw in other entries that after market cats don't have enough catalyst and the CEL will just light again. Anyone with an aftermarket California cat have a good experience?
 
#6 ·
Also Thanks, schmiddr2, I'm a very hands-on problem-solver for someone my age and gender...not afraid of manuel labor, etc. I've very mechanically inclined, like my dad....taken all sorts of appliances apart and fixed them, etc. Not much work on the cars, unfortunately.
 
#7 ·
I kept getting this code on my son's Corolla. I ended up having to change both the upstream O2 sensor (it's an A/F ratio sensor on the Avalons as I think you already know) and the downstream O2 sensor. It took me by surprise that the recently installed aftermarket upstream sensor had to be changed too. I'm convinced that it's best to stick with the OEM Denso brand sensors for everything. Search Amazon for deals.
 
#8 · (Edited)
2000 Avalon XLS P0420

I've have and continue to trouble shoot the P0420 for about a year. I guess you could say that I'm intrigued by the code and why the code turns off a critical safety feature. I own a Bluetooth device that provides live feedback of the engine's performance including "codes". I can also clear the codes (follow the manufacture instructions).

In my case, the VSC lamp would appear randomly after I cleared it. In time, after tuning the engine, the lamp would only appear after I drove around 50 miles or so. It didn't make a difference if the miles were city or highway miles. Several months had gone by and I started experimenting with gas additives like Seafoam and others. I didn't have any success with any of them even with the products that claimed they cleaned Catalytic convertors.

With that being said and since I've mentioned catalytic convertors, here is some insight on how the O2 sensors and catalytic convertors work together. Keep in mind I'm not a mechanic and the following is not a complete description. Of the many systems that use feedback from the O2 sensors their principle job is related to engine emissions. The feedback from the o2 sensors can gauge if the catalytic convertors (2 upstream and 1 downstream) are performing as they were designed. When connected to scope (oscilloscope) the two upstream frequencies vary constantly (up and down peaks). However, the downstream sensor remains at 1 - a flat line (more or less). If, while the engine is running, one of the upstream o2 sensor's frequency peak reaches 1 or greater, the VSC lamp will appear. In short, that is why one could say it's the catalytic convertor - but which one is the question. Obviously, the two upstream catalytic convertors should run hotter than the rear. Because this subject can become much more complicated than the scenario I've described I'll stop at this point.

Also, take note that the O2 sensor reads the ratio of O2 within the exhaust. With that said, I've managed to reduce how often the VSC lamp appears by adding gasline antifreeze to my gas - yes, even in Florida! In fact, all Floridians and snowbirds should add a water remover to their gas every fill up. By doing doing so, the gas once mixed with O2 burns more efficiently, thereby, the O2 sensors are happier (more often). A clean burn is better. To add, use the recommended spark plugs for your vehicle (hopefully it's in your owners manual) , which excludes all replacements or substitutes.

Hope this provides some insight - good luck
 
#9 ·
Thanks so much for posting. I've learned a lot from this forum. I really like the Avalon and I hope this car doesn't develop a lot of problems...it seems to run OK. I can live with erasing the P0420 for a while longer until I decide what to do next.
 
#10 ·
Okay, bare with me because I know this may sound FAR FETCHED.

Just recently, on Nov. 20/16, my check engine light came on and I read the P0420 code with my cheapy OBD2 reader. This happened after driving a few miles after a fill-up. I suspected the gas cap seal because this happened to me once before. The top rim of the gas tube was a bit rusty so I, once again, carefully smoothed it with some fine emery cloth so as not to get any fillings into the tank. Then I smeared some grease onto the sanded rim and the rubber O-ring of the gas cap. Then I tightened the cap as much as possible, even trying to go beyond the "clicking".

It's Nov. 27/16 now and the P0420 hasn't returned. Just to repeat, this has happened to me once before and solved it the same way, back whenever. Whether this works for you, who knows, I'm just relaying an experience(s) I've had.
 
#11 ·
Jus a WAG (wild @$$ guess) here, and I could be totally out to lunch. Didn't some Lexus vehicles have 4 O2 sensors; 2 pre-cats and 2 post-cats? Could it be the ECU is looking for cats that aren't there and interpreting this as a fault in the circuit and throwing a code?
 
#12 ·
Thanks for the suggestions, jbeez2000 and MacQ. I will definitely have a look at how the gas cap seals, as well as check into how many O2 sensors are present in this car. I would like to exhaust all possibilities before replacing the catalytic converters.
 
#13 ·
The ECU would only be looking for a 4th O2 sensor if it was the Lexus ECU. The Avalon ECU would only be looking for 3. Ask your mechanic if he switched the ECU when he did the engine swap. I think it's more likely the A/F ratio sensors, especially if it's an aftermarket brand. My niece's Avalon kept throwing codes even with a new A/F sensor until she switched to a Denso sensor.
 
#14 ·
Does the car consume oil? Or, in other words, even though you don't see a leak or smoke coming out the exhaust, does the oil level on the dipstick go down often or consistently? If so, this is probably the reason for the P0420. Oil is being burned and going out the exhaust manifold and then to the catalytic converter. It is then coating the inside of the cat with burned oil. This abates the efficiency of the catalyst materials to do their job, which then is picked up by the downstream 02 sensor, which turns on the light and the P0420 code. Removing the cat and cleaning/soaking it in soapy water may very well work, but the problem will come back if the engine still burns oil. It's also easier to use lacquer thinner in the gas tank, as this will clean off the inside of the cat without having to remove it. Again, it's temporary if the engine burns oil. My son has a '96 Camry that burns oil. So, every 6 to 10 months the P0420 lights up. We put lacquer thinner in the tank and the light doesn't come back for 6 to 10 months. Yes, it works (if the engine burns oil), because when the code is cleared, the catalyst monitor completes and is ready. It comes back because the car still burns oil and eventually coats the inside of the cat again.

On my '04 Corolla, the P0420 was fixed by replacing the original downstream O2 sensor, which had 298K miles on it, I think. The upstream sensor was still working fine, but I replaced it at around 300K anyway.
 
#15 ·
:clap: Ah Good Thinking John Anthony!
I once read a statement from an exhaust system specialist. He said "Catalytic Converters don't die. They are murdered!" He went on to explain that the catalyst is not consumed during the chemical reaction that occurs within the converter, so they never wear out. Essentially the only reasons for a converter to need replacing is if the catalyst is prevented from working due to being coated with oil or coolant..... the engine was replaced due to blown head gasket(s). Certainly there would have been a significant amount of coolant (and likely oil too) going down the exhaust system and thus a converter failure would be very likely.
Since the mechanical problem was rectified with the new engine, I would think that this/these converter(s) is/are prime candidates for cleaning. There are dozens of videos & techniques that are reported to help. I would start with the easiest ones and if necessary remove and wash them. I have no experience with doing this, so perhaps some suggestions and research are in order. If that works, I believe your troubles will be over.
P.S. converters can also get loaded up with excess fuel and burn internally or be physically damaged by running over something, but that does not apply in this instance.
 
#16 ·
the catalyst is prevented from working due to being coated with oil or coolant..... the engine was replaced due to blown head gasket(s). Certainly there would have been a significant amount of coolant (and likely oil too) going down the exhaust system and thus a converter failure would be very likely.
Duh, yes I should have seen that like you did. It is very probable that this is the result of the previous engine's headgasket problem. Thanks for pointing that out. That's good news, since once it gets cleaned, it shouldn't be a problem anymore assuming the replacement engine is not burning oil. In any event, the cat is most likely coated with burnt something that is preventing it from working.
 
#17 ·
That's one of the great things about this forum. When people bounce ideas off each other a light bulb goes off and the solution becomes clear. I can't tell you how many times I've been stumped on a problem, but when I tried explaining it to someone the answer became obvious. That's why everybody should :my2cents:
 
#18 · (Edited)
Update

First, thank you to everyone who responded to this thread! I appreciate your ideas!
Here's my update about how the P0420 went away.
FINALLY the P0420 which showed up at least 2-3 times per month for the last 8 months, seems to be gone. The CEL came back on and instead of P0420, it showed P0136. The mechanic changed the B1S2 and I haven't had a problem since!!
Changing the downstream sensor was mentioned over and over in this forum as an intervention for the P0420 code. Some months ago when I first got the P0420 code I mentioned this to my mechanic but he said the voltage of B1S2 was ok when he tested it. So the sensor must have been failing all these months and finally died. It would have been worth it just to have changed the sensor months ago even though the voltage was ok in that moment of testing, since the downstream sensor was the likely culprit.
Thanks again for all the great info on this forum!
 
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