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Discussion Starter · #1 ·
Hi I'm learning how to DIY with different cars

A 2003 corolla is showing a p0420 code and the o2 sensor voltages also don't seem to be as they should. Both are fluctuating indicating a non-catalyzing converter.

My question is about what may have caused it and although it is pretty obvious to me that the cause is that this car has gone low on oil and/or has seen high Temps (boil over around oil cap),

I just wanted to ask about other pointers, seeing that I don't want the new $400 catalytic converter to get ruined when it gets installed.


Thanks
 

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Cats fail for all types of reasons. Sensors can also fail for all types of reasons.

It would be nearly impossible for to pinpoint an exact cause on a 13-14 year old Corolla.

Did you recently purchase it? Is it burning oil or leaking oil? I've never heard of "boil over" at the oil cap. It's most likely just spilled oil from a previous change.

If it's a recent purchase, read here:

http://www.toyotanation.com/forum/1...e-common-problems-potential-buyer-thread.html
 
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You should also replace the oxygen sensors when you replace the cat. Denso and NTK (NGK) are the best oxygen sensors to use.

Burning and leaking oil can ruin the cat, Misfire issues can allow raw gas into the cat (which is why a misfire codes cause the CEL to blink, to alert you of something that can damage the catalyst), like bad spark plugs and/or fuel injectors. A leaking valve cover gasket/spark plug seal can allow oil to flood the plugs.

You also don't have to spend $400 on a new cat. eBay has them for about 1/3 of that.
 

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Discussion Starter · #4 · (Edited)
Thanks. One of the spark plugs did have oil on it. I guess I should replace the plugs. I wasn't sure how to tell if plugs were bad. I do have pics of the plugs. Could that alone help the NOx code go away?

I have already put a new valve cover gasket on it, that's when I looked at the plugs. And a chain tensioner o-ring. So in other words, it WAS leaking oil, but I'm not sure if it was burning oil...

I was using bafx Bluetooth obd2 scanner and torque app.

you're probably right about oil being spilled while adding oil. But it did overheat. I think the Cat was damaged during that overheating

I was looking at eastern catalytic for a cat and resonator kit for $381. No welding necessary :) I can't really do the whole welding thing... Harbor freight MIG $269..... But I just want an easier cheaper quicker fix. EC Cat kit $381, versus a shop charges $700 for it done with whatever parts, not sure

I found the denso O2 sensors $40-55 each

I saw the cheaper Cats on ebay but I need CARB and don't want to do welding. cutting would not be so bad, but a carb cat w/o the resonator is not much less, might as well buy a new resonator so it fits well with the cat and call it a day. Hoping it would last a while. Guaranteed for 25k miles. How long do you think these after market Cats last if the car is taken care of?
 

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Sorry, didn't know you needed a CARB cat. Eastern does make good quality parts. And it should be very easy since you don't have a rust problem.

The good news is that California requires a 5-year/50k warranty (which is why they cost more than 49-state converters that are only required to last 2-years/25k). BUT you have to take care of the oil leak issue! Damage to the cat caused by another issue, like oil burning or a bad fuel injector, is NOT covered. In a mechanically sound engine, cats are not a regular maintenance item, so as long as it doesn't burn or leak any oil, you will not have to replace it again for as long as you have the car.
 

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19 Corolla HB SE 6-spd
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I see it here, Eastern Catalytic # 809581. It includes both cats and the resonator. Two halves are joined and sealed with one exhaust pipe clamp. It could always get welded after it's installed and more convenient... Flange gasket (donut) is included.

http://showmetheparts.com/easterncatalytic_ca/

You should also get a set of 2 new bolts and springs. Dorman # 675221.

http://www.rockauto.com/en/catalog/toyota,2003,corolla,1.8l+l4,1432914,exhaust,bolt+/+spring,10741


Also, there is an ECU recalibration available to raise your P0420 threshold, as per TSB EG028-04:

https://www.discountconverter.com/tech-tips/news_page.cfm?Key=catalytic_converter-&News=228
 

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Discussion Starter · #7 · (Edited)
About the oil leak issue. I put a new valve cover gasket, PCV valve, chain tensioner o-ring and did an Engine Flush additive and then put in new synthetic oil. Then degreased it with Gunk, and it hasn't gotten dirty for a couple months. I doubt it burns oil but I'm not sure how to tell. I don't think it burns much if any. what's the best way to know if it burns oil? check the dipstick?

wow good info about the TSB. What does that cost to have them reflash the ECM/PCM? I doubt they would cover it since the OE Cat on the car must be out of warranty and all... 2003 240k miles

It could always get welded after it's installed and more convenient
good point, thanks
 

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19 Corolla HB SE 6-spd
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Yes the engine oil level on the dipstick will show how fast it goes down over thousands of miles, as there is about 1 quart difference between upper full mark and lower add mark... Your oil capacity was also revised. It was increased by 1/2 quart, simply by raising the dipstick marks by nearly 1/2", as per T-SB-0134-08. Your revised full mark is at exactly 18" from center of o-ring near dipstick handle. Just make a new full line with a marker.

http://www.toyotaparts.metro-toyota...L_LEVEL_SPECIFICATION_UPDATE_T-SB-0134-08.pdf

An ECU recalibration takes about 1/2 hour labor... You can confirm with your Toyota dealer first.
 

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2004 Corolla with 307K now. Earlier this year the recalibration cost me $109 at Red McCombs Toyota in San Antonio. There are several other Toyota dealers in this big city and they were all more expensive than that, so I just called around and got the best price. The most updated calibration is the one you want (the number ends in 300). Replacing my downstream 02 sensor finally fixed the P0420 (in conjunction with the ECM reflash?). On a funny note, one of the Toyota dealers told me that there was no recalibration available on such an "old" car. They were either completely ignorant, or they just wanted to sell me a new car.

Some of the 2003 Corollas still had the old piston design with fewer oil passageway holes in the pistons. You may have had stuck rings, which caused oil to burn and coat the cat. This can cause a P0420 eventually because the catalyst material is covered in the residue of this burned oil. My son's Camry had an oil burning problem and when we used lacquer thinner in the gas, the P0420 went away after the entire tank of gas was used up. Switched to a thicker oil, which didn't burn and now many months later the P0420 has not come back.
 
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Discussion Starter · #10 ·
How much lacquer thinner did you use per tank/half tank?

I started putting in mobil 1 synthetic extended 5w-30 10k miles ago. I'm not sure if the NOx code came up before that or after.

what oil should i switch to if this is indeed the problem and the lacquer thinner works?

thanks for all the helpful info
 

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Just use 5w/30 synthetic. The problem with my son's Camry is that the previous owner didn't take care of the car and it was just getting worn out.

Here's the info for the lacquer thinner in this video. It really does work if the problem is burning oil that has coated the cat. If it's some other problem with the cat, then it won't work.

 
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FYI:

Lacquer thinner IIRC is mainly MEK, aka Methyl Ethyl Ketone. Gasoline contains some ketones. Kinda harsh on bare hands and v. flammable. Keep in original container, dissolves some plastics and glues. Good luck.
 
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