CEL P0420 - CAT deficiency

T4R_Finally

T4R_Finally

New member
I just got rid of my RX8 to buy a 3rd gen. For several reasons, but one of them was because it randomly threw emissions related codes and I'd have things checked and nobody could ever find a problem. Had the CAT checked by a dealer and they said it was fine. O2 sensors checked out fine.

So, I bought this 3rd gen with high hopes. Seems well maintained, has a good carfax history, and is super clean. It looks and runs great. I went to pick it up yesterday and the CEL was on before I made it 10 miles down the road. I stopped at the first Advance Auto I saw and the code was a P0420. They reset the code for me and I shot an email off to the previous owner. He claims the light never came on for him. So, I've got 200 more miles ahead of me, so I fill up with gas and cruise on. About 20 miles from home, the light comes on again. Checked it this morning and same code. Reset again and hasn't come back on yet. Also, checked the air filter and it was about as nasty as I've ever seen one. I bought and through in a drop-in K&N filter. I highly doubt the filter could have caused a CAT related code but it needed replacing anyway. As all of this was going on, the truck never hicupped. Ran like a boss and still does.

I've searched this forum and have found other reports of this code along with a lot of discussion about it being a bad sensor or a bad CAT. And, I read and already know without checking that a dealer is going to tell me it's the CAT. I'm trying to figure out if it's worth changing the sensor(s) or if I should just bite the bullet and take it somewhere and get the CAT work done. And looking for any suggestions on what my options are. I live in rural NC and in a county where they still don't require an emissions test to pass inspection. But I can't assume it's going to always be that way because many other counties in the state do require that.

If it's worth changing the sensors, where is the best place to get them and how hard are they to replace?

Any input would be appreciated.
 
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I've posted on this several times before but here we go again.

My cat is know to be failing. It took two tries to get the truck up to enough heat to pass smog last time, and even then the numbers were not that stellar. My cel only comes on once and a while. Usually low speed cruising, slow trail driving, basically anything that we cover a decent distance with out ever getting the RPMs up.

From your description I would guess it is the sensor itself that is bad. Seems like yours comes back on even in normal driving conditions. It could also be that the cat is completely done, but you didn't mention a strong exhaust smell.

As far as replacing the part doesn't get much easier than an "o2 sensor".

Some guys have posted about getting the OE Denso part on amazon or other places. Personally I find the Toyota dealer that will give me the best prices/service and stick with them for most of the parts that I need. Even if I could save a few $'s on an item here or there, the continued business usually gets me service and prices beyond an ordinary one time customer. I also buy more than the average Toyota owner so this may or may not work for others.
 
Aren't there 2 O2 sensors? Is the post-CAT one likely to be the one I want to replace?

You are correct stick, I didn't report any exhaust smell because there is none and there is nothing noticeable about the way it runs before or after the CEL. And, it was normal, highway driving conditions. I bought this from a guy almost 300 miles away and I went and got it and drove it home last night. The first time the light came on, I was on a city street and was going about 40mph. But after I had it reset, I drove it maybe another 200 miles at anywhere from 55 to 70 mph all the way and it just randomly reappeared about 20 miles from my house - 2 lane highway, cruise control set at about 60.

So, is the sensor easy to get to, remove, and replace? Any chance I'll have issues getting it loose? Would some PB Blaster help that maybe? Can't hurt to have a new sensor, no matter what the actual problem turns out to be. So, I think I'll just go ahead and change it.
 
Both o2 sensors are held in by two 12mm nuts. Not very difficult to remove/replace. If you look at the exhaust at about the front doors, you will see one in front of the cat, one after. Shoot the nuts with some PB the night before, and they should come off smoothly. Make sure that you have a new gasket as well. Sometimes you can get away with reusing the old one, but it's cheap insurance.
 
Stick Figure said:
Some guys have posted about getting the OE Denso part on amazon or other places. Personally I find the Toyota dealer that will give me the best prices/service and stick with them for most of the parts that I need. Even if I could save a few $'s on an item here or there, the continued business usually gets me service and prices beyond an ordinary one time customer. I also buy more than the average Toyota owner so this may or may not work for others.
Click to expand...

Amazon is definitely way cheaper than the dealer, I show $110 at the cheapest online dealer, and $55 on Amazon.
 
Nelsonmd said:
Amazon is definitely way cheaper than the dealer, I show $110 at the cheapest online dealer, and $55 on Amazon.
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I hate amazon .. won't order anything from them unless I absolutely have no other choice. and you are missing the big picture.... If a shop or store treats me well and give me a good price and service on almost everything I don't mind paying more once and a while to support them. When i want OEM ball joints, amazon won't help me out, but that guy behind the counter that knows i've spent thousands with his company will. When I need some dealer only info, amazon won't be able to help, that guy in the parts dept might be able to.

Just the way I do business. Getting the lowest price once isn't always my top priority.
 
a GOOD PRICE HAHAHAHA that's DOUBLE what Amazon wants. Just because you have something against amazon, doesn't mean the rest of us don't. Even with overnight shipping it will still be significantly cheaper than the local stealership. FYI my local dealership is a bunch of dipwads. They lost my security lugnut wrench on my Toyota Supra Turbo, they told me they couldn't order various misc parts, they tell me I have to order "complete units" rather than simple replacement parts when I can figure out how to order the same simple parts online. Anyway I can get out of NOT dealing with local stealership is what I WOULD DO!
 
SJC4Runner said:
a GOOD PRICE HAHAHAHA that's DOUBLE what Amazon wants. Just because you have something against amazon, doesn't mean the rest of us don't. Even with overnight shipping it will still be significantly cheaper than the local stealership. FYI my local dealership is a bunch of dipwads. They lost my security lugnut wrench on my Toyota Supra Turbo, they told me they couldn't order various misc parts, they tell me I have to order "complete units" rather than simple replacement parts when I can figure out how to order the same simple parts online. Anyway I can get out of NOT dealing with local stealership is what I WOULD DO!
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Then I wouldn't shop at your local dealer. I would find one that knows what they are doing. I drive by several Toyota dealers to get my parts, whats your point?


and once again you missed the entire point I was making. and for what its worth no Toyota dealer has ever lost a part of my Toyota Supra Turbo because I've never needed to take it in for service, I do order parts from them however.
 
Guys, if you don't mind, back to my thread. LOL

Appreciate the feedback. For me, it will be easier to order online because I live over an hour from the nearest dealer. I don't mind ordering an OEM part, however, and paying a little more for it. Is what people are ordering on Amazon the exact same thing as what you buy in a dealership or is it a cheaper "equivalent"? I'm not a big amazon fan either. Nothing against them, I just find other online resources easier to use, for me.

So, at this point, my question is - should I replace both 02 sensors, or just the one behind the cat, and are they the same part # or different? And does anyone have or know where I can find the part number(s) for the sensors and gaskets as well?
 
AFAIK The part number for MY2000 is= 234-9002 (Denso) For the front that is. And 234-4153 for the rear
 
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I just went through this (sequoia though). Three things could cause P420. Bad o2 sensor, bad cat or leaky exhaust. 02 sensor would have its own p code though.

More then likely, the cat is poisoned.


I would try cooking the cat first. Need to put the 4runner under a heavy load to get the cat really really hot. It will burn off all the impurities. Probably need to power brake it and gas it going up hill. Don't warp your brake rotors.

Just my two cents though.
 
Singtoe said:
I just went through this (sequoia though). Three things could cause P420. Bad o2 sensor, bad cat or leaky exhaust. 02 sensor would have its own p code though.

More then likely, the cat is poisoned.


I would try cooking the cat first. Need to put the 4runner under a heavy load to get the cat really really hot. It will burn off all the impurities. Probably need to power brake it and gas it going up hill. Don't warp your brake rotors.

Just my two cents though.
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Which other code are you talking about for the sensor failure? Only one i'm thinking of off the top of my head is the heater code, and the sensor can fail but still provide enough resistance for the heater circuit to be happy.
 
Singtoe said:
I just went through this (sequoia though). Three things could cause P420. Bad o2 sensor, bad cat or leaky exhaust. 02 sensor would have its own p code though.

More then likely, the cat is poisoned.
Click to expand...

A bad rear O2 can throw a P0420 and no other code. Mine did. I don't think it's 'more than likely'--based on my own case and several other posters on this board. The real question is how many people dumped good OEM cats when all they needed was a new rear sensor. Unless you have visible overheating, sulfur smell in the exhaust, noise from a broken substrate, degraded performance suggesting blockage, or other evidence of a bad cat, I'd say it's at least worth the cost-benefit return to try a new sensor before buying a new cat. I did and it's been three years now.
 
Sure, check on the 02 sensors, they are a lot cheaper then a cat .

But what I was suggesting was to cook off the impurities that might be in the cat. If that doesn't work, Then replace the o2 sensor and if that doesn't go, then replace the cat.

Going from cheap to less cheap and then to expensive.
 
awdjunkies said:
AFAIK The part number for MY2000 is= 234-9002 (Denso) For the front that is. And 234-4153 for the rear
Click to expand...

Before i order one of these rear sensors, can someone confirm the part number for my 2000 limited 4x4? Or point me to a resource to confirm for myself? I did some searching, and realize they are probably found on multiple models and years. But couldnt find anything that specifically said it would fit my yota. Found some that referenced late 90's lexus.
 
T4R_Finally said:
Before i order one of these rear sensors, can someone confirm the part number for my 2000 limited 4x4? Or point me to a resource to confirm for myself? I did some searching, and realize they are probably found on multiple models and years. But couldnt find anything that specifically said it would fit my yota. Found some that referenced late 90's lexus.
Click to expand...

See my post #10 above for the link to the Denso catalog. Exact number depends on manual/auto and Cali./49-state and you have not posted that info (that I can see).

EDIT Well, Limited means auto but need to confirm Cali. or 49-state.
 
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My truck was originally purchased in maryland. Do i assume its not a cali or would it be stated on the window sticker? Would the owners website have specific info? I am on a fishing boat today so dont have access to the owners site.Lot of traffic before raleigh. Stopping in tarboro to get a burger
 
Just throwin' this out there... I tried to go the cheap way on the O2 once & bought the "not Denso" ones.. They didn't last long at all.. Denso is twice as much but unless you look forward to seein' your CEL come on every yr, pay the xtra.. I'm not a salesman by the way... Just tryin' to help...
 
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