If you don't trust your mechanic's diagnosis watch the following vid to figure out how to diagnose a bad cat for yourself. It may indeed just be a bad o2 sensor (expensive but not as expensive as a new cat):

 

To greatly extend the original life of the catalytic converters the owner must do everything possible to minimize the concentration of hydrocarbons in the exhaust that reaches the converters in the first place. The practical ways an owner of a new Toyota can do that over a period of 10 years or more are: 1) Change the engine oil every 3000 - 5000 miles instead of 10,000. 2) Change the spark plugs at 50,000 miles instead of 100-120,000 and use the same plug the engine came with. 3) Clean the throttle body plate of accumulated deposits every 30-50,000 miles. 4) Change the pre-cat oxygen sensor(s) every 75,000 miles using an identical Denso replacement instead of waiting for them to deteriorate to the point where the check engine light comes on. 5) Drain and refill the engine coolant with the exact same coolant every 3-5 years or 75,000 miles to keep the radiator free of deposits that could cause higher than normal coolant temperatures.

Of course a used Toyota bought off craigslist will not have received these timely services over the years, hence the cats are routinely degraded enough by 75,000 - 170,000 to set a catalyst efficiency below threshold trouble code. It's possible, but not guaranteed, that replacing the oxygen sensor(s) ahead of the cat(s), changing the spark plugs and cleaning the throttle plate will minimize the concentration of hydrocarbons that reaches the converters sufficiently to prevent a catalyst efficiency below threshold trouble code from reappearing after the original code is cleared. It's very important to use Denso oxygen sensors and spark plugs that have the same part numbers as the originals.

 

Your cat is most likely just fine... Start with a proper tuneup with new spark plugs, and replace your leaking intake manifold gasket for revised orange silicone gasket # 17171-22060.

 

I was definitely thinking of replacing the spark plugs, as I am unsure of when they were last replaced. What makes you recommend replacing the intake manifold gasket? I don't notice any leaking. Thanks!

 

www.toyotanation.com/forum/132-coro...9-diy-2003-2008-corolla-matrix-pontiac-vibe-intake-gasket-replacement-pics.html

http://www.toyotanation.com/forum/1...-2005-2006-corolla-xrs-2003-2006-matrix-xrs-vibe-gt-spark-plug-replacement.html

http://www.toyotanation.com/forum/1...2130-diy-2003-2008-corolla-matrix-pontiac-vibe-maf-sensor-removal-cleaning.html


Toyota orange silicone gasket # 17171-22060 / MAHLE MS19590 https://www.rockauto.com/en/catalog...og/toyota,2006,corolla,1.8l+l4,1432846,engine,intake+manifold+gasket+/+set,5424

DENSO 4701 Iridium TT (or DENSO 4503 Platinum TT) https://www.rockauto.com/en/catalog/toyota,2006,corolla,1.8l+l4,1432846,ignition,spark+plug,7212

 

Wow, thank you all for the replies and wealth of information! I'll be sure to replace these parts.

 

You want to know ROOT CAUSES, but I can only tell you a couple stop-gap temp solutions:

1. TC-W3

The smog test tests for Carbon monoxide and something else, right? Well WalMart and many others sell this stuff called TC-W3 that binds and eliminates those two things. The weird thing is that's oil for JET-SKIS, bro..! Someone was watching them blub around the marina and marveled at that thick blue smoke that comes up; some scientist checked it out and it turns out that Jet-skis and many outboard boats emit in just ONE HOUR the equivalent emissions as an average USA passenger car emits in A YEAR..! Amazing, huh..? So there was a great enviro hue and cry, and they invented this TC-W3 stuff in order to diminish that problem that marine outboard motors have; maybe they require using it, I don't actually know, since my jet-skis days on Lake Tahoe have sadly ended.. About a week before your smog test you put 3 ounces into a full tank of gas and you drive that down --you WILL pass. A chemist on Toyota Nation at first was incredulous but he ehcked out the MSDS and it turns out the patent for TC-W3 contains some acid which he confirmed will do the trick.

I don't know but I think if u used 3 ounces of this stuff every time you fill up it's possible you could htake some of the stress of your cat for now, until you can find a firm, permanent solution.

2. Autozone part 42009,

This part fits in the palm of your hand and they're "Spark Plug Non-Foulers". YouTube has maybe 3 vids on exactly how to, eh....adapt and then use this part. For off-road purposes, OF COURSE. You'll need a common hand-drill and a 1/2 inch bit and maybe 10 minutes of your time before going off-roading.

 

It's actually 2 ounces of TC-W3 2-stroke outboard/jet-ski oil in 10 US gallons of gasoline, or 666:1... Better to wait before trying that though, as the cat may be overwhelmed by combustion of the extra oil and released carbon and contaminants as it cleans combustion chambers, etc.

http://www.ls1.com/forums/f48/been-testing-oil-91206/

 

Did you ever find out about this?. I have the same exact code, except that my wife has owned this car from day one.

Here's what I had in mind:

Replace both O2 sensors, the car is now around 145,000MI.
Clean up the MAF

 

properly diagnose the cat code per the video above before replacing the o2 sensors.

on a code scanner with live data capabilities the pre-cat o2 sensor voltages should fluctuate between rich and lean. if the pre-cat o2 sensor doesn't oscillate then it's likely bad
the post-cat sensor should be stable. if it oscillates as well then the cat is most likely bad.

the actual temperature of the catalytic converter should be hotter after the catalytic reaction

 

So today I changed my spark plugs and intake manifold gasket and cleaned the MAF sensor and throttle body. As I disconnected the battery a couple times to do this work, my CEL has gone away, but I'm sure it will come back on soon.

I've attached pictures of the old spark plugs and intake manifold gasket. The spark plugs don't look too bad, and neither does the gasket. In fact, neither look like factory, so I'm guessing they were changed at some point and might not be the cause of the bad cat.

Anyone have any thoughts based on the images/work done?

 

Intake manifold gasket always needs to be replaced on these gen corollas.

iridium spark plugs are good for 100k Miles.

If you want to diagnose your cat you need an OBD scanner with live data capabilities:

https://www.amazon.com/Innova-3040e...525GNFR/ref=sr_1_1?ie=UTF8&qid=1524372617&sr=8-1&keywords=innova+live+data&th=1

 

File limit exceeded in last reply! Here are the rest of the images. These are just two of the four spark plugs, because they pretty much all looked identical in terms of condition.

 

You already had the revised gasket, but your spark plugs' threads were very rusty. I had a P0420 appear as soon as mine misfired for the same reason... Yours should be okay now. If the code reappears, I'd suspect a weak downstream O2 sensor.

 

Yeah, the code reappeared yesterday. What's the best way to self-diagnose the downstream O2 sensor? And can you link me to a DIY guide to replacing it? The ones you sent previously were great!

 

http://www.toyotanation.com/forum/1...081-diy-downstream-oxygen-sensor-replacement-2003-2008-corolla-lots-photos.html


"Inspect your new sensor (optional). Once removed, compare the old sensor side by side with the new sensor to verify they are the same. Using your digital multimeter set to measure resistance (ohms), check the resistance value of the heater circuit of the AF/O2 sensor and verify the sensor is good before install. The heater wires are the two black wires located at the top of the connector... If I get a signal side failure, I'll test that part of the circuit which is also a resistance test."

2006 Downstream O2 sensor heater circuit (black wires): 5-16 ohms at 68°F
2006 Upstream O2 sensor heater circuit (black wires): 1.8-3.4 ohms at 68°F

http://www.toyotanation.com/forum/1...-2008-corolla-matrix-pontiac-vibe-1zzfe-upstream-oxygen-sensor-replacement.html


DENSO 2344233

https://www.rockauto.com/en/catalog.../toyota,2006,corolla,1.8l+l4,1432846,exhaust+&+emission,oxygen+(o2)+sensor,5132

 

Thanks invader! You're the best. Sorry I have so many questions. Do you recommend doing both the downstream and upstream sensor?

 

The upstream sensor on 2005 and up is a Wideband Air/Fuel Ratio sensor instead of an oxygen sensor. They're more expensive but tend to last longer I think... 112,000 miles on yours? They usually recommend replacing between 60,000 and 100,000 miles.

DENSO 2349052
https://www.rockauto.com/en/catalog.../toyota,2006,corolla,1.8l+l4,1432846,exhaust+&+emission,oxygen+(o2)+sensor,5132

 

I do use a wideband A/F ratio sensor to monitor and determine fuel adjustments made with Camcon fuel and cam timing controller on my 2004... My sensor is still well functional but fails to recognize exceedingly rich A/F ratios after about 100,000 miles of use.

 

Thanks all!

1) Will keeping this cat on my car damage anything else over time?

2) Do I need to get a digital multimeter? I feel like if I buy the new sensors there's no point in testing the old ones.

 

Posting in here to get an idea of why my CAT might have gone bad. I've got an automatic 2006 CE with 111k miles. The car passed smog on March 5th. Just bought the car off Craigslist on March 10th, and the CEL came on after driving it about 85 miles. Seller is ducking my calls, so no luck there. Took it to O'Reilly to get the code read (pictures attached). Then took it to a mechanic who told me the 02 sensors were both reading at variable wavelengths and recommended that both catalytic converters be replaced. He didn't tell me anything about what might have caused the CAT to go bad in the first place, even when I asked. I know they don't just deteriorate out of nowhere, so I want to find out and fix what ruined it before I get a new one.

I don't really have any symptoms besides the CEL, as far as I can tell. Gas milage is not far off from normal (26mpg), there's no sulphur smell, not idling rough, can reach and maintain speed of 80mph, doesn't have trouble shifting gears or accelerating up hills, starts perfectly fine every time, doesn't misfire.

Please help! I don't want to rack up bills going to mechanics replacing a bunch of parts, as I know catalytic converters can deteriorate for many reasons. Thanks for reading! Let me know if there's any other lucrative information I might have left out on accident.

If both pre and post o2 sensors are variable then your cat is probably dead. Only the pre cat should vary - a properly functioning cat stabilizes the o2 levels and so the post cat o2 sensor should be flat.

You can either replace the cat $$$ or put on a spark plug non-fouler onto the post cat o2 sensor which stabilizes the post cat waveform and will prevent the CEL from coming back.

 

moogor: You likely have some time until the cat damages your engine. This repair is not a big deal. You can do the anti-fouler but be warned that tampering with the emission systems is illegal in some states.

I replaced the catalytic converter in my 2006 Camry for $500 total. I bought a cat from one of the Toyota vendors here on ToyotaNation and had my mechanic install it. It took him an hour of labor time to do it. I waited about 4-5 months from the first "check engine" light to replace it.

If you're handy, you may be able to install it yourself. In the Camry, the cat is pretty accessible. Go to www.rockauto.com to get a price.

Good luck.

 

Sure, your upstream wideband A/F ratio sensor and downstream O2 sensor may still be variable, but not necessarily sufficiently. They may no longer be operating at an acceptable level.

No, a cat that is no longer efficient enough can not harm your engine in any way. In fact, you don't require a cat at all. It'd be better to remove it altogether if it ever clogs up, which is highly unlikely. It's there for emission purposes only.

 

I had cel problem with cat code on scanner,
along with lacquer thinner (a gallon) in my corolla tank and drove on high way, cel did not disappeared
I am sharing with you folks that worked in my car
I sprayed through O2 sensor holes............Berry-man B12 carburetor cleaner
on 2 different occasion with 4 days apart directing at the cat
after spraying waited for 15-20 minutes then took for a 20km hyway trip
I do not have CEL almost 2 months and on obd2 scanner tool my cat comes as green (good)
hope this helps, credit goes to all the testers at toyota form and youtube guys.