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DTC code sez Oxygen Sensor Heater Circuit (Bank 1, Sensor 1). I have '01 Tundra SR5 4x4 and just rolled to 100k. I thought it was maybe some coincidence with Toyota telling me I should do some kind of 100k maint.

Anyway, is this something me, myself and I can fix? I do small stuff but wouldn't take on a tranny for example, so I'm not afraid to loosen a few nuts and drop a new part in if that's what it takes. Where to get it, what to buy, how hard is this to correct?

-Don
 

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Don~

Yep. Right on the money. 100K is the expected lifespan of the heated air-fuel/oxygen sensor.

It's a fairly straightforward remove/replace IF you don't have a heavily rusted exhaust manifold and the unit isn't seized in place. It is the front, driver's side sensor throwing the code. If you can change out spark plugs, you can do this and save yourself some $$$. A substantial percentage of this service bill at the dealer is labor, on top of which they also gouge you on the sensor units themselves. I've removed and reinstalled all four of mine just to inspect and get a good application of anti-seize on them.

Note that when one side goes, the other side is probably not far behind. I strongly suggest you replace both banks while you're already under there. Why pay shipping twice? My $0.02.

> > > > For the correct sensor, go here: Denso part lookup page < < < <

For your 2001 Tundra V8 SR5 4X4:

Here is the sensor you need: Denso, #234-4169. Amazon has em for about $40. Both sides take the same one. (first pic, below) Resist the impulse to try a cheaper aftermarket or other brand part here. This is an ECU-related component, and you'll have problems, guaranteed. I'd also steer clear of the "universal" models that require you to resplice the wiring into the old connector. Just to save a few $$$? On a component that should last another 100,000 miles?

You will also need a specialty socket that has a cutout to allow you to work around the attached wires. Your local auto parts supply should have one in stock. There are a couple different styles. I've seen them at Harbor Freight for about $5 as well. (fourth pic below)

The upstream sensors are located under the rearward end of the exhaust manifold, just forward of the exhaust pipe flange. For best access, lay with your head facing towards the front and reach back and over the front crossmember. I have a 2" lift and I don't even need to jack up the truck to do this. You can remove the skidplate to facilitate the procedure, although it isn't necessary. (see the fifth pic below for a view of this sensor)

Give the base of the sensor a good soaking of PB Blaster, WD-40, Kroil or some other penetrating lube and let it sit overnight. As you are working at the exhaust manifold, I suggest you do the R/R on a COLD engine. It is also to make sure that the manifold is not in an expanded state from heat. Chilton suggests that if the sensor is hard to remove, you might want to start and run the engine for a minute or so, shut it off, and try it again. Be careful! The sensor, manifold, and exhaust will all be HOT! Be especially careful of the intake tube end of the sensor... the inside gets heated to 1500F!!

Then, the steps to remove and replace are:

1. Unplug the wire harness connector.
(It is gray, and will be up about 7" or so from the sensor. You might try using a small screwdriver to push down on the little retaining tab so the connector half will slide out. Take your time here. It can be a little finicky. This part took me longer than the actual sensor to remove.
* * * SUGGESTION * * *
For those with really gummed up upstream O2 connectors, you might try cleaning one of the rears first with some CRC MAF Cleaner and practice disconnecting one of those so you can see how they are configured; they are WAY easier to access. Trying it blind reaching up on the manifold is a pain.)

2. Get the sensor socket on it and remove.
This can be tricky. Try using different length socket extenders, if needed, to assist with the reach {thanks to RocketChild for the tip!}. A seized sensor is NO fun. Use the PB Blaster liberally. Start to unscrew the sensor, and if you get serious resistance, hit the threads with the lube and then screw it back in. Do this a few times; it should work its way out. If it doesn't, I'd suggest letting the dealer or a trusted local shop do the work. Some people feel comfortable putting a breaker bar on it to get it loose, but it is my opinion that you don't want to be at home with stripped out manifold threads. If this happens, I'd bite the bullet and invest in some JBA or Doug Thorley headers anyway and call it a day.

3. Apply anti-seize compound (available at your local auto and marine supply stores, see pic below) to the threads of the new sensor. Denso normally includes a little tube of it with their sensors. There are only about 3 or 4 threads on these units, so just use a little and make sure to keep any compound away from the sensor's input ports. I'd also apply a very thin film on the seating surface as well.

4. Carefully start threading the unit in by hand. Take your time. They're in a position that is hard to see.
(Just like spark plugs, you do NOT want to cross thread these.)

5. Apply the sensor socket carefully to the sensor.
(Make sure you do NOT get the wires bound up.)

6. Torque to specs. (TSM states 32 ft/lbs. I think this is a little high, especially with the anti-seize, so I torqued mine to about 20-22 ft/lbs. Your call.)

7. Reconnect the wire harness connector(s).

8. To clear the code (if any), either get a OBDII-compliant code reader or disconnect the negative terminal on the battery for half an hour or so to drain all residual system/ECU memory, reconnect, and drive. The code should be gone.

Done. :nod:

Do not skip the step of using the anti-seize. Sometimes you will get a package with your sensor unit. Sometimes not. A tube is only about $6.

Note that if you can get these done by yourself, when the time comes to do the same to the downstream (BX/S2) ones, they are WAY easier. They are a little more expensive. On the 2000-2004 model years, you don't need the O2 socket, but the TSM suggests you replace the metallic gasket and mounting nuts. (second pic below, location view on the last pic below). The 2005-2006 4.7L model years' downstream sensors thread into the cat directly just like the fronts.

Also note that on some model years of 4WD Tundras, there are different model number specifications for the rear sensors than with the 2WD models. It is the same sensor but one side has a little longer wiring harness to account for driveline geometry of the 4X4. Crosscheck carefully to assure the right sensor for your truck.

> > > > For the correct sensor, go here: Denso part lookup page < < < <

Let us know how it went for you. :tu:

- Remmy700P


* * * A Note About Oxygen Sensor Wire Harnesses * * *
Oxygen sensors thread into the exhaust system where they face extreme heat, violent impacts from road debris, and harsh exhaust gases. One reason oxygen sensors fail is when the sensor bulb inside is exposed to lead, silicone, antifreeze, engine oil and other contaminants. But, many people are not aware of the role that the other end of the oxygen sensor plays. Surprisingly, the visible end of the sensor with the wire pigtail is just as important and sensitive to contamination as the end slugging it out in the exhaust pipe.

Combustion engine vehicle oxygen sensors are designed to measure the difference between the oxygen level in the exhaust with the oxygen level in the outside air. The sensor generates a voltage based on the difference in oxygen levels that the ECU uses to continuously adjust the fuel mixture, etc. The outside air the oxygen sensor needs for its comparison enters the sensor at the end with the wire pigtail. Depending on the sensor design, the air might enter through a dedicated hole on the connector or through the wires themselves.

The oxygen sensor ambient air inlet is likely to be protected by silicone boots, porous PTFE (Teflon) or some other means. A routine splash of water is not likely to hurt an oxygen sensor, but leaking chemicals (engine oil, power steering fluid, etc.) can clog or enter the oxygen sensor air inlet and damage the sensor. Efforts to “protect” oxygen sensors by spraying them with lubricant, covering them with insulation, etc. can backfire if the sensor’s air inlet is blocked or contaminated.

Oxygen sensor installation instructions emphasize that the entire sensor, including the wiring harness, is part of an integrated system. Routing and connecting the wires is as important as carefully threading the sensor into the pipe.
 

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Great summary by Duffy. It is as easy as he says and can save you hundreds if you do it yourself. Just be sure to get the special sensor socket (has a slice in it to slip it through the sensor wires and then onto the sensor). Also, if you are not too crazy about splicing wires then get an OEM sensor with the stock connector already on it. Some non OEM sensors require you to cut the old connector off and splice the new sensor to it. As far as identifying the proper sensor to replace, search the threads on here and you will find it (I can't remember which side is which). Good luck!
 

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Great step by step guide. I have a 2000 tundra 4.7 are the sensor that I need the same part # as the 01 4x4?. I also have the P0155 and P0161 errors also, I'm assuming the same procedure do you happen to have the part #'s of the other 2 sensors that I need?

Thanks in advance,
Chris
 

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Great step by step guide. I have a 2000 tundra 4.7 are the sensor that I need the same part # as the 01 4x4?. I also have the P0155 and P0161 errors also, I'm assuming the same procedure do you happen to have the part #'s of the other 2 sensors that I need?

Thanks in advance,
Chris
Go to the Rock Auto website and plug in your vehicle info. It will give you the sensor(s) you need.
 

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Discussion Starter #7
Duffy,

Thanks for great instructions, and writeup. I finally got around to doing this, ugh, yea this morning so that I could get SMOG'g by EOM, yikes I know, well I made it!!! My removal/install wasn't too bad, I didn't have a skid plate so I could just work around the pipe, but yea kinda a tight fit, as my biggest problem was getting them unplugged. The right sensor was wanting to resist though, so I gave it some WD-40, then twisted maybe 1/4 turn back and forth, let it sit for 10 mins, then finally it came out. I
reinstalled with the lube, gave it "two fingers" torque, then reset the check engine codes and off I went...beautiful, Duffy you're a GURU!

-Don
 

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Duffy,

Thanks for great instructions, and writeup. I finally got around to doing this, ugh, yea this morning so that I could get SMOG'g by EOM, yikes I know, well I made it!!! My removal/install wasn't too bad, I didn't have a skid plate so I could just work around the pipe, but yea kinda a tight fit, as my biggest problem was getting them unplugged. The right sensor was wanting to resist though, so I gave it some WD-40, then twisted maybe 1/4 turn back and forth, let it sit for 10 mins, then finally it came out. I
reinstalled with the lube, gave it "two fingers" torque, then reset the check engine codes and off I went...beautiful, Duffy you're a GURU!

-Don
Good news Don! Thanks for the update. Glad it helped ya out... and saved you some $$$! :tu:
 

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I have a 2001 Tundra 4WD with 42,000 miles on it ... do you think I should do the timing belt soon or can I base it more on mileage than time ? Thanks in advance !
 

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I have a 2001 Tundra 4WD with 42,000 miles on it ... do you think I should do the timing belt soon or can I base it more on mileage than time ? Thanks in advance !
I've struggled with the same question as well; it doesn't have an easy answer.

As you can see from my sig below, I have an '02 that only has 48,000 on the odo. An independent Toyota ASE mechanic I've spoken with says environmental degradation has almost as much impact on the belt as pure miles driven. Therefore, it would depend on where you live/drive. I live in a fairly moderate climate with winters only down to the 40s and summers periodically into the low 100s, so I'm going to wait 'til about 55,000 miles to do it which, for me, works out to around the middle of next year.

HTH.
 

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Outstanding. I performed this over the weekend and had zero problems. Something that really helped I believe is that I did this in 34 Degree weather. So the pipes were ice cold. I put the vehicle up Friday night when I got home and went out later in the evening and sprayed with the PB Blast. Went back out Saturday Morning, afternoon and evening and did it again. Sunday Morning, went out and began work. It really helped to have two extra items. One I used a pipe extension on my wrench and two, I used a 18in socket extender. This allowed me to get out of the way of the manifold/engine/frame. Popped loose on first go.

On a second note, I was able to rent a torque wrench and the O2 sockets from AutoZone. It was a lot for the deposit ($130) but I'll get my money back when I return the tools this evening.

Out the door, I spent $140 replacing both front O2 sensors. Oh yeah!

Thanks Duff for your post, it gave me the info that I needed to knock this out.
 

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Well just did bank one sensor one with out anything other then the special tool some pb blast and elbow grease thank you all for the information on how to fix this issue. even with buying the o2 socket and torque wrench still saved 200. thanks again
 

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Problem with rear sensors...

First, I want to thank everyone here for the great info on replacing the sensors - it made the job much easier. I was getting the PO135 AND PO155 codes, plus PO446.

I bought all 4 sensors, was able to replace the 2 fronts, but the 2 downstream sensors are giving me major problems. The nuts just crumbled when I tried to remove them. What can be used to remove the rest of the nuts, without damaging the threads on the bolts?

I feel like I should replace the rear sensors, since now there isn't much holding them in place. One of the nuts on the driver side is completely gone, and none of them are holding the sensor in place too well.

It figures that the 'tough' front sensors actually went pretty well, and the easier more accessible rears are giving me fits.

Ken
 

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Re: Problem with rear sensors...

First, I want to thank everyone here for the great info on replacing the sensors - it made the job much easier. I was getting the PO135 AND PO155 codes, plus PO446.

I bought all 4 sensors, was able to replace the 2 fronts, but the 2 downstream sensors are giving me major problems. The nuts just crumbled when I tried to remove them. What can be used to remove the rest of the nuts, without damaging the threads on the bolts?

I feel like I should replace the rear sensors, since now there isn't much holding them in place. One of the nuts on the driver side is completely gone, and none of them are holding the sensor in place too well.

It figures that the 'tough' front sensors actually went pretty well, and the easier more accessible rears are giving me fits.

Ken
Ken, it's all going to depend on how deep the corrosion has gotten. If it's eaten away at the post, you probably have to run a die over the stems to recut the threads. Worst case scenario, you'll have to cut off the remainder of the posts, drill out the rest, and reinsert new threaded bolts. I know some here have installed the rear sensors by jamming smaller diameter nuts onto worn threads. It works, but isn't the right way to do it.

Also, make sure to replace the oval metallic gasket when replacing the downstream sensor units to avoid exhaust leaks.


* * * PREVENTATIVE MAINTENANCE TIP * * *
Periodically check the level of corrosion on the rear oxygen sensor nuts. Replace them before they get too far gone. Make sure to use some anti-seize on the threads. It's cheap insurance and will save you a ton of headaches down the road.
 

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Thanks Remmy. I think the posts are still OK, I'll take a look with a good light. What can be used to remove what's left of the nuts from the posts?

Also, the local Toyota dealer parts guy tells me that the nuts are a special order... Do you have any idea what size they are?
 

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Thanks Remmy. I think the posts are still OK, I'll take a look with a good light. What can be used to remove what's left of the nuts from the posts?
There are seized nut remover sockets available. I've seen multi-size packs at Summit. You can try those first. However, I'd imagine that they're gonna cause all kinds of damage to the underlying threads.

Also, the local Toyota dealer parts guy tells me that the nuts are a special order... Do you have any idea what size they are?
Not offhand. There's a thread either in here or in the Gen-1 forum that states the size. I'd do a search of both threads using "O2", "sensor", and "nut" and see what comes up.
 

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Try using an 18" socket extender to assist with the reach {thanks to RocketChild for the tip!}... Some people feel comfortable putting a breaker bar on it to get it loose, but it is my opinion that you don't want to be at home with stripped out manifold threads.
How in Hades would you get an 18" extender in there - much less a breaker bar?

On my 2002 Tundra, the front O2 sensors are almost completely surrounded by heavy-duty structural steel.

I can just barely even reach a hand up in there.

For best access, lay with your head facing towards the front and reach back and over the front crossmember.
I'm not exactly sure what you're saying, but I can barely reach up in there.

Unplug the wire harness connector... Trying it blind reaching up on the manifold is a pain.
No kidding - I can barely get one hand up there - how am I supposed to get two hands up there to hold the thing when I try to re-connect it?







Finally, how in HADES did you get the camera angle to take those pictures?

I just don't see any way I could even hold a camera to take the pictures you took.

[I am so p!ssed off at Toyota right now - for putting such a crucial piece of hardware in such an impossible-to-reach location - that I could spit.

God bless it.]
 

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How in Hades would you get an 18" extender in there - much less a breaker bar?
For me, as I recall doing it a year ago, when I said "I put my truck up" I had rolled it on ramps. This gave me a bit more length to be able to slide my extender in there. I recall what you were saying, about having a lot of steel in the way (V8). But it was kind of a snake process, plus I wore a headlamp so I could see up to where I was going. It was not a huge challenge, more just tinkering with getting all the angles lined up (and maybe attaching the driver after all the extenders are in place).

Besides being on cold concrete, this was really a piece of cake! I wish others luck...especially those that have severe oxidation and rust. Now, with the cold weather, is the time to do it too! I say that and it is 80 degrees here in Texas in Mid-February.
 

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I'm resurrecting this thread because I'm about to embark on a similar project.

I started getting the CEL warning so I broke down and got a ODB II scanner which is showing a P0135 code which I believe is the Bank 1, Sensor 1 O2 sensor.

The repair seems pretty straight forward and I'm willing to take this one on, but I'm a little confused about which sensor is Bank 1, Sensor 1. I don't want to replace the wrong one.

BTW, all the O2 sensors were replaced under the 90,000 extended warranty; I can't believe they've gone bad again.

BTW, mine is an '01 AC, 4WD.
 
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