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This is what I would do if I planned to keep the car:

1). Get the manuals. It looks like there is a set on EBay right now for about $50 + $20 for the wiring diagram. A good deal.
2). Reset the check engine light and see if codes return.
3). If other codes besides P0420 or P0430 occur, address those codes first and reset the CEL.
4). If the P0420 or P0430 occurs by itself, get all four of the Denso oxygen sensors, available from Rock Auto for less than $400. There are tests in the manual to diagnose the sensors, but they require either Techstream or other pro level scanner and time, which may cost about the same as just replacing all the sensors.
The sensors might clear the codes and even if new cats are needed, old sensors could reduce its life.
If you just need to get the car through inspection, then do the diagnosis or just replace the bank 2 sensors one at a time to see if that will get you through. The sensors do wear out. They typically function well up to somewhere between 100k and 150k. I would probably start with Sensor 1.
5). Address any issues which may have caused the cats to fail, including high oil consumption especially through the PCV system and loss of coolant into the intake manifold, and rich or misfire conditions.
Good luck.
 

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Discussion Starter #42
Thank you for all of the replies. Yes, I do not have a check engine light. For now, I'll wait and see like you said. The odblink app can monitor both O2s. Some reason during the real time monitor, O2 sensor 1 wasn't showing any voltage. Will test it again when I have access to the car. I'm assuming O2 sensor 1 would mean bank 1 but the P0340 code is for bank 2.

I had no idea these have problems consuming oil. It's due for a change, I'll see how much I drain from it. Coolant level looks about the same. Also the timing belt and water pump were never replaced, a failing water pump can also cause coolant loss right? I'm not sure if it has an exhaust leak, I have to get under it. I don't believe their are any leaks in the engine bay but I will check again. No abs light on right now, the other 8 codes were on after I disconnected the battery overnight. The car hasn't been driven much lately but I will keep updating. Do you think the ODB fusion app is better?
 

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Looks like OBD Fusion and OBDLINK are one and the same. I have not used OBDLINK but looking at it briefly it seems to run the monitors and reports as well as storing logs and graphing. I can’t tell if it will allow upgrade to the extended PID’s which allow access to the transmission, abs, etc. That might be the reason to get OBD Fusion some time in the future but for this problem it looks like OBDLINK will work well.
For sensor designation:
Sensor 1 is the sensor before the catalytic converters. It is often called the AF or air/fuel ratio sensor. There is a sensor 1 for bank 1 and another sensor 1 for bank 2.
Sensor 2 is the sensor downstream of the catalytic converter. It is often referred to as the heated oxygen sensor or the HO2S. There is an HO2S for bank 1 and a separate one for Bank 2.
You should be able to find Toyota Technical Service Bulletin T-SB-0398-09 on line which explains it clearly for the 3MZ-FE engine.
Coolant loss will only affect the catalytic converters if it is being pulled into the intake manifold or cylinders. If you are losing coolant and can see where it is going there’s no risk to the cats.
If you are losing coolant and you cannot see where it is going that you should look farther to make sure it is not getting into the cylinders.
No concern about contaminating the cats from a water pump, but if the timing belt has never been done, it is overdue if you are going to keep the car.
Many vehicles have problems with oil consumption through the PCV system due to clogged valve cover gaskets these days. I have heard speculation that it is from the newer API service SM and SN oils, or maybe the way the overhead cam VVT engines spread oil, but I have not heard a definite answer.
When choosing oil, pay attention to the API service rating. In my opinion the SN oils are not necessarily the best for older engine life. The service rating for your engine is on the oil filler cap. I would follow it. Look up ZDDP for more information.
Good Luck.
 

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This is what I would do if I planned to keep the car:

1). Get the manuals. It looks like there is a set on EBay right now for about $50 + $20 for the wiring diagram. A good deal.
2). Reset the check engine light and see if codes return.
3). If other codes besides P0420 or P0430 occur, address those codes first and reset the CEL.
4). If the P0420 or P0430 occurs by itself, get all four of the Denso oxygen sensors, available from Rock Auto for less than $400. There are tests in the manual to diagnose the sensors, but they require either Techstream or other pro level scanner and time, which may cost about the same as just replacing all the sensors.
The sensors might clear the codes and even if new cats are needed, old sensors could reduce its life.
If you just need to get the car through inspection, then do the diagnosis or just replace the bank 2 sensors one at a time to see if that will get you through. The sensors do wear out. They typically function well up to somewhere between 100k and 150k. I would probably start with Sensor 1.
5). Address any issues which may have caused the cats to fail, including high oil consumption especially through the PCV system and loss of coolant into the intake manifold, and rich or misfire conditions.
Good luck.
Greetings from Charlotte NC. Bought my 2004 Highlander 2 years ago from original owner-- currently 221,000 miles. Has 3.3 V6 FWD and nearly no options -- not even daytime running lights. My 3200 pound rocket! Love the car.

I replaced all 4 oxygen sensors last year (Denso from RockAuto) and noted smoother engine and cleaner exhaust smell. Old ones were OEM with the tiny plastic tags on the wire near each sensor.. Gas mileage up 1mpg city and highway. Big change was spark plugs-- nearly certain I removed the OEM Denso plugs from the rear bank. Found gap erosion out to .083 inch due to eroded ground tangs. Gas mileage up 2mpg on highway, with near odorless exhaust once warmed up a bit. No carbon inside tailpipe. Went with BKR6EIX plugs -- note lack of -11- extender. These come factory gapped approx .036 inch. Noted smoother engine with new plugs, more consistent to drive. My car drives great on 89 Octane MidGrade, plus I now get 29mpg highway at 70mph. Definitely suggest the Original Poster change all 4 (or 5 on his car?) oxygen sensors, plus make sure the spark plugs are either NGK or Denso, and not badly worn like mine were. Using Toyotra T4 fluid in my trans, and Toyota Red for engine coolant. Nearly no oil burning. If intake manifold is removed please replace your valve cover gaskets while access is good. My engine oil is Mobil One 5W30, and oil filter is oversize -- the filter for a 1991 Ford Escort SOHC fits perfectly but is over 5 inches long. Wix oil filters have better anti-drainback valves than Purolator-- mine is 51516 at Wix, 1516 at NAPA (same filter).

I owe huge thanks to many people on this forum. I have lurked for several years, now time for me to stick my head up. My hobby is Fuel and Ignition -- I enjoy working on emission equipment. Yes I am partially crazy.
 

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Welcome BeeBow.
Good points about the plugs and filters.
I change my plugs at 80k. Worn plugs can reduce gas mileage, cause drivability issues, and kill coil packs.
I picked up about 2 mpg when I changed plugs and all 4 sensors at 82k shortly after I got my 2005 Limited AWD.
 

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Discussion Starter #46
Thank you for your input BeeBow. Will be replacing all plugs, went with Denso. Also will be buying O2 sensors. Pricing out timing belt kits and wanted to know if replacing the hydraulic tensioner is necessary.
Are their any aftermarket catalytic converters for the 3.3 that are carb compliant? C R you were right, New York doesn't allow the sale of used catalytic converters. I did find a wrecked 2007 highlander with 80,000 miles that I might be able to take it from.
 

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Walker is one of the better aftermarket brands but they do not make one for California according to their site.
I would call the best auto parts store in the area to see what you can get.
Since it is bank 2, you only need that side. The best price I find online for OEM parts is from McGeorge Toyota.
If the 2007 parts are OEM and available that sounds pretty good.
 

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Thank you for your input BeeBow. Will be replacing all plugs, went with Denso. Also will be buying O2 sensors. Pricing out timing belt kits and wanted to know if replacing the hydraulic tensioner is necessary.
Are their any aftermarket catalytic converters for the 3.3 that are carb compliant? C R you were right, New York doesn't allow the sale of used catalytic converters. I did find a wrecked 2007 highlander with 80,000 miles that I might be able to take it from.
Hello Tyler426. Suggest some work first before you spend a sackload on catalytic converters. Suggest you change out the spark plugs (save the old ones or take good pix for later diagnostics-- note cylinder number on plug) also change all 4 (or 5?) oxygen sensors. Note other posts on ToyotaNation-- if your hands are small the rear 3 plugs may be replaceable with intake manifold still in place. Must use Denso O2 sensors or you will do it again. Yes I know that the front sensors are expensive-- sorry! Do it once and do it right. Also please buy from RockAuto or Toyota or a good Auto Parts Store -- avoid Amazon or eBay or some PepBoys stores due to way too many fake parts in realistic appearing packaging. Clear the Check Engine trouble codes if possible. Once you have the correct spark plugs in it, correct O2 sensors, hopefully you can take the Highlander for a drive. You may (hopefully) get a surprise-- the CEL may not come back on! I also suggest adding some good fuel injector cleaner to the fuel just before a big drive. I prefer Chevron Techron Fuel System Cleaner.

My usual procedure for fuel injector cleaner is to add it to my gas tank, fillup with fuel (91 Octane or better) then immediately begin a 40-60 mile one way drive on freeway. After 5 miles, (And when traffic permits) at least 4-8 times I apply 1/2 to 2/3rds throttle for a few seconds. It helps to coast down to a slower speed then apply throttle-- watch out for traffic! Any speeding tickets are your responsibility. Resist temptation to floor the accelerator-- flooring it makes engine computer command rich mixture which will add carbon inside your engine. What this 1/2 throttle stuff is doing is make the engine work harder, longer fuel injector pulse, with only moderate increase in engine speed, and avoids a drastic transmission downshift and screaming engine. Now that you have driven 40-60 miles, you need a "hot soak" for the engine. Stop somewhere for lunch, go shopping, whatever. The stopover should be 45 to 120 minutes in length. Restart Highlander, and drive back home-- again apply deeper throttle 4-8 times on the way home. On most of my homeward bound drives, I am noting increased part throttle power. When I get home, the exhaust smells cleaner-- often odorless, which is good. After this drive, go ahead and use car normally, and run the fuel tank down to 1/8 to 1/4 tank before refueling. I have done this injector cleaning procedure to over 30 cars, including many Toyotas, some Fords, and GM products too. All have improved fuel economy (1 mpg or so) plus cleaner exhaust smell once warmed up.

You may need to clear any CEL trouble codes again, then drive car normally. I have failed (Subaru) and succeeded (some Toyotas, GM, and Ford) in "rescuing" wounded catalytic converters. Your own car may give different results. Literally you have little to lose doing this except the cost of the fuel injector cleaner, lunch, and fuel for the drive. The rest of the work you needed to do anyway. Regarding timing belt kits-- some folks compress (slowly) and re-use the hydraulic belt tensioner, but why not replace while you are in there? Suggest the Aisin belt kit, or the more expensive Contitech kits-- note that Gates timing belt kits are now using cheap (Chinese etc.) components (Pine Hollow Auto Diagnostics busted Gates cold on a Subaru kit -- see YouTube). Suggest you have someone experienced help you with the timing belt job, or have a trusted shop install the timing belt kit you have purchased. I have over 40 years experience, and a Toyota V6 belt job still scares me!

If converters must be replaced, a used converter off a real Toyota would be best financially-- unless you want to pay for Genuine Toyota Parts. Here again, avoid eBay. Pay attention to replacing any gaskets etc. at the connect points. You may need to replace more than just the converter if the donor Highlander is a different year. But, who knows what other parts will "fall off" that wrecked Highlander? Coil packs? Factory radio? Rims/tires? Deep thinking here!

Sorry for the long reply. Welcome to ToyotaNation! Do lotsa reading on here, and thank the many helpers we have here! I have learned so much, but still have much to learn.

BeeBow
 

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Discussion Starter #49
Hello Tyler426. Suggest some work first before you spend a sackload on catalytic converters. Suggest you change out the spark plugs (save the old ones or take good pix for later diagnostics-- note cylinder number on plug) also change all 4 (or 5?) oxygen sensors. Note other posts on ToyotaNation-- if your hands are small the rear 3 plugs may be replaceable with intake manifold still in place. Must use Denso O2 sensors or you will do it again. Yes I know that the front sensors are expensive-- sorry! Do it once and do it right. Also please buy from RockAuto or Toyota or a good Auto Parts Store -- avoid Amazon or eBay or some PepBoys stores due to way too many fake parts in realistic appearing packaging. Clear the Check Engine trouble codes if possible. Once you have the correct spark plugs in it, correct O2 sensors, hopefully you can take the Highlander for a drive. You may (hopefully) get a surprise-- the CEL may not come back on! I also suggest adding some good fuel injector cleaner to the fuel just before a big drive. I prefer Chevron Techron Fuel System Cleaner.

My usual procedure for fuel injector cleaner is to add it to my gas tank, fillup with fuel (91 Octane or better) then immediately begin a 40-60 mile one way drive on freeway. After 5 miles, (And when traffic permits) at least 4-8 times I apply 1/2 to 2/3rds throttle for a few seconds. It helps to coast down to a slower speed then apply throttle-- watch out for traffic! Any speeding tickets are your responsibility. Resist temptation to floor the accelerator-- flooring it makes engine computer command rich mixture which will add carbon inside your engine. What this 1/2 throttle stuff is doing is make the engine work harder, longer fuel injector pulse, with only moderate increase in engine speed, and avoids a drastic transmission downshift and screaming engine. Now that you have driven 40-60 miles, you need a "hot soak" for the engine. Stop somewhere for lunch, go shopping, whatever. The stopover should be 45 to 120 minutes in length. Restart Highlander, and drive back home-- again apply deeper throttle 4-8 times on the way home. On most of my homeward bound drives, I am noting increased part throttle power. When I get home, the exhaust smells cleaner-- often odorless, which is good. After this drive, go ahead and use car normally, and run the fuel tank down to 1/8 to 1/4 tank before refueling. I have done this injector cleaning procedure to over 30 cars, including many Toyotas, some Fords, and GM products too. All have improved fuel economy (1 mpg or so) plus cleaner exhaust smell once warmed up.

You may need to clear any CEL trouble codes again, then drive car normally. I have failed (Subaru) and succeeded (some Toyotas, GM, and Ford) in "rescuing" wounded catalytic converters. Your own car may give different results. Literally you have little to lose doing this except the cost of the fuel injector cleaner, lunch, and fuel for the drive. The rest of the work you needed to do anyway. Regarding timing belt kits-- some folks compress (slowly) and re-use the hydraulic belt tensioner, but why not replace while you are in there? Suggest the Aisin belt kit, or the more expensive Contitech kits-- note that Gates timing belt kits are now using cheap (Chinese etc.) components (Pine Hollow Auto Diagnostics busted Gates cold on a Subaru kit -- see YouTube). Suggest you have someone experienced help you with the timing belt job, or have a trusted shop install the timing belt kit you have purchased. I have over 40 years experience, and a Toyota V6 belt job still scares me!

If converters must be replaced, a used converter off a real Toyota would be best financially-- unless you want to pay for Genuine Toyota Parts. Here again, avoid eBay. Pay attention to replacing any gaskets etc. at the connect points. You may need to replace more than just the converter if the donor Highlander is a different year. But, who knows what other parts will "fall off" that wrecked Highlander? Coil packs? Factory radio? Rims/tires? Deep thinking here!

Sorry for the long reply. Welcome to ToyotaNation! Do lotsa reading on here, and thank the many helpers we have here! I have learned so much, but still have much to learn.

BeeBow
Thank you for your reply BeeBow, the more information the better. I will be trying the procedure you gave for saving the catalytic convertor.

I will be buying the Aisin kit from rockauto. I was quoted $375 without parts to replace everything in the kit. The mechanic(not the one that ripped me off before) said he would replace the cam and crank seals. I know that's a great price from browsing the forums here. I was wondering what brand for the cam and crank seals you would recommend. Attached screenshots of the choices from rockauto, I know I only need the front seals. I can't find a post with the seals listed besides the genuine Toyota "brand."

Also should the thermostat be replaced too? They're inexpensive and the coolant will be drained anyway.
 

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If it has not been replaced, the replace it. Have the mechanic check for coolant leaks around the coolant inlet plates between the heads.
 
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