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Air/Fuel & O2 sensor mini write-up

44K views 60 replies 27 participants last post by  CafeRoaster 
#1 ·
Just did both air-fuel sensors and both O2 sensors on my 2008 today. I didn't find much in write-ups for this work so I figured it was either super easy and nobody needed it or not many have done it. Either way, here is what I did and a problem I ran into. Nothing earth shattering but maybe it will help someone considering doing on their own.

Symptoms leading up to the replacement: I was having some off idle hesitation up to about 2500 RPM or about 35MPH but it wasn't 100% of the time and nothing I tried could make it happen or make it stop. I posted a thread in the engine performance section about the issues I was having and got a lot of good advice. I cleaned the throttle body and bought a blue tooth OBD2 reader to get a better look at what was going on. I didn't have any codes but something wasn't right. After cleaning the throttle body (off engine) and taking a test drive with the OBD2 reader reporting on the Air/Fuel ratio commanded and the Air/Fuel ratio monitored nothing jumped out at me right away but I did notice that sometimes there was a pretty big Delta between the two and they were not really closely matched all the time. I was still running the OEM sensors and in the other thread had learned I was well past what was an expected life for all of them. I decided to go ahead and swap them all out in effort to restore the lost performance.

Specailty tools I used:
OBD2 Bluetooth
Torque Pro App
Lisle Dual Drive O2 offset wrench
Lisle O2 thread chase
I used Denso A/F ($108) and Denso O2 ($48) sensors from Rock Auto

Normal tools I used:
I didn’t keep a comprehensive list, I replaced all 4 sensors from underneath and I did use several 1/2" extensions with the Lisle wrench on the A/F sensors, 3' extension with U joint on the passenger side exhaust bracket upper 14mm bolts (from engine compartment), 14mm ratcheting box end on the driver’s side exhaust bracket upper bolts, 22mm box end wrench for the O2 sensors and 3/4" ratcheting box end wrench on the Lisle thread chase. The wiring harness plugs are set free by way of a standard screw driver with a narrow head and about a 3-4" length.

Drivers side A/F sensor:
The FSM alludes to removing a bracket with 3 bolts and by the picture in the FSM I wasn't sure what it was. Once under the driver’s side I saw what was in the way - a big bracket with two bolts on the engine block side and a single bolt on an exhaust coupling. Removing these bolts took a lot of effort and a cheater bar, which had either a bunch of torque from factory or had just taken a hard set over the years/miles.

Once the bracket was out of the way I was able to use a short/narrow standard screw driver to release the wiring harness from the sensor pig tail. I used the O2 wrench with 1/2" drive extension as a handle and a short cheater bar to get the A/F sensor to break free. Once the sensor was broken free it unscrewed by hand pretty easy. I ran the chase in/out the threads with little to no resistance. I coated the new Denso A/F sensor threads with their provided copper colored anti-seize and ran the sensor into the threads by hand until lightly seated. Once it was seated I used the Lisle O2 wrench to seat the sensor with a reasonable amount of torque.

Passenger side A/F sensor : The exhaust bracket was a PITA to remove. I could only reach the two upper bolts with a 3' extension and a U joint. Even then it took a cheater bar to pop each one free. The bottom bolt came out without issue. Getting the wiring harness free took the narrow standard screw driver but by the time I had my arm up where it needed to be I couldn’t see the plug so I had to do it by feel. Took me a couple tries to unplug the sensor. Removing the A/F took the Lisle O2 wrench but this time with a 3/8 socket wrench in the top side of the O2 wrench and a cheater bar on the socket wrench handle. Once it popped free, it was easy to un screw by hand. I ran the O2 thread chase in/out with little to no resistance, applied the copper color anti seize and installed the A/F sensor.

Drivers side O2 sensor : The sensor unplugs same as the A/F sensor with the short narrow standard screw driver. I used a 22mm 12 point box end to unscrew the sensor (the pig tail on the sensor fits through the box). The O2 sensor was tough to break free and just as tough to unscrew to remove. A couple times I stopped to make sure I wasn’t accidentally tightening it by accident. I even pondered if it might be reverse threaded for some reason. In the end it came out with a lot of effort. The threads on the old sensor looked like crap and I was worried it might have galled the threads and I was right. The threads in the exhaust pipe were in bad shape. It took a couple starts to get the O2 thread chase started square but once started I would turn it in about 1/4 turn and then back it off 1/2 turn or more and run it back in another 1/4. I pulled it out to clean and relube several times. It took a while but I eventually got the threads re-cut and cleaned up. I was able to install the new sensor with the copper anti seize without drama.

Passenger side O2 sensor: After all the drama on the driver’s side I was a little hesitant to pull this sensor out. I was able to unplug the pig tail and pop the sensor free without drama. This one unscrewed by hand once popped free and the thread chase ran in/out with little resistance. I coated the threads of the new sensor with the copper anti-seize and installed it by hand and set the final torque with the 22mm box end wrench before plugging the pig tail back in.

I re connected the negative side of the battery and started the FJ. It fired right up to a pretty fast idle, like it would on a very cold day (it was about 75F today). The initial idle seemed to have a little roughness to it but there were no apparent exhaust leaks or dash warning lights. I shut off the engine, plugged in the OBD2 scanner and started the engine. I ran through the scanner readings and everything seemed to be ok with no codes. I took a couple runs around the block and everything ran great. I took a longer test drive after cleaning up and its very noticeably better. Throttle response is back to what I remember and everything is smooth at idle. The initial idle roughness I felt at first start went away fast and everything settled in during this longer test drive.

I am really happy I bought the O2 thread chase! Both Lisle tools were great quality (forged) and I am pleased with both the pruchases. I almost skipped the chase but I would have been SOL today without it. I have no idea what happened with the threads in the drivers side O2 sensor, maybe I somehow messed it up while unscrewing it or maybe it got jacked up when it was installed on the assembly line. I'll probably never know but I am damn happy I had that thread chase and was able to recover from that situation.
 
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#35 ·
Toyota gives them 3 part numbers because the wire harness length for the O2 sensors is different.
When you buy the much less expensive Denso version the sensor is the same as you'd get from the dealer but the wire harness is more universal (you may have to zip tie some excess in some cases). This is how they can make them for less money: standardized parts = lower inventory costs.
 
#36 ·
If you buy the Denso "OEM Identical" sensor, it is EXACTLY the same as the original equipment, and EXACTLY what you'd get if you bought it from a Toyota dealer. Exact same cable length, exact same color connector housing, etc.

If you buy a Denso "Universal" sensor, it is the same sensor but supplied unterminated (without connector). You are supposed to cut the connector off of the old sensor, splice it on to the new sensor, and save $10. Because of the low level signal, the splice must be soldered, carefully insulated with high-temp shrink-fit tubing, etc. Not worth the $10 savings.

Buying from densoproducts.com (a major Denso distributor in the US) will usually be a significantly less than the dealer price. Rock Auto can also give good pricing on genuine Denso products.
 
#37 ·
Man, I had to admit defeat trying to access those sensor plugs. At least temporarily.

I'll try again later, or maybe recruit my double-jointed kid.

I tried from the top.

Skid plates are still on below and those are always a headache to remove.
 
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#38 ·
Man, I had to admit defeat trying to access those sensor plugs. At least temporarily.

I'll try again later, or maybe recruit my double-jointed kid.

I tried from the top.

Skid plates are still on below and those are always a headache to remove.
I suspect the best access is from below or maybe through the wheel well (with tire/wheel off) but I don’t think any route is great. Elastic-man would make a great mechanic. 😀
 
#39 · (Edited)
I used a long extension out the wheel well and to the top of the tire.... with it jacked up a bit.
The tire was the perfect height to "back up" the ratchet extension.

I heated it pretty good with a MAP gas torch and it cracked loose, and busted an extension in the process, lol. I was pretty surprised the sensor had cracked loose - overjoyed actually.

I NEVER want to do those again. Tore up my arms pretty good reaching in.
Those damn plugs are hard to unplug AND to plug back in!

The plugs were done strictly by feel.

The fancy sensor socket.... I used the backside of it from thru the wheel-well.

Once they cracked loose I removed them by hand. The new ones I thread in by hand and used a 2" extension on the ratchet on the driver side.... I used it as "normal" on the passenger side - again, that was done by feel. I put it on and into position by flipping the ratchet to clockwise or counterclockwise, all by feel. Once it was in position I then tightened it, mm by mm.

Driver side;
Outerwear Glove Product Textile Sleeve



Passenger side
Household hardware Gas Nickel Metal Auto part
 
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#41 ·
Yeah, they came with anti seize already on the threads.
 
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#44 ·
"I’ll just leave it unless the FJ springs a CEL. Sounds like a major PITA." - ok, but don't complain if its mpg ever does suffer (or, at least know that could be the reason why). :)

By the way, if the exhaust support brackets are able to be removed that makes access pretty good (wheels/tires off, side shields off, working from below). But, due to rust, they are often not possible to remove and so the use of several extensions and a swivel or two get needed.
 
#45 · (Edited)
I just did all 4 sensors and the MAF a few weeks ago. Here are the part numbers I used. I also bought the offset O2 tool and the thread chase on the first post of this thread.

The sensors are Denso from Rock Auto.

EDIT: This was for a 2007 manual FJ Cruiser.
Rectangle Font Material property Parallel Slope

I was lucky and none of them were seized after 160,000 miles. I had the front wheels off for a brake job so I pulled a couple of clips off the rubber fender liners and went in from the side for unplugging the connectors. On the left (driver's side) I unbolted the front drive shaft where it goes into the front diff. On the right (passenger side), I removed the exhaust brace (2 bolts in engine and 1 on the exhaust). Then with a LONG 1/2" extension stuck in the end of the offset wrench I was able to pop the upper ones loose. It was surprisingly easy considering what I've read on this thread! I consider myself lucky.

If anyone in the Colorado Springs area wants to borrow the offset wrench and thread chase and wants a hand, let me know. The # of beers owed is proportional to how badly they are seized :D
 
#46 ·
I just did all 4 sensors and the MAF a few weeks ago. Here are the part numbers I used. I also bought the offset O2 tool and the thread chase on the first post of this thread.

The sensors are Denso from Rock Auto.
View attachment 1208456
I was lucky and none of them were seized after 160,000 miles. I had the front wheels off for a brake job so I pulled a couple of clips off the rubber fender liners and went in from the side for unplugging the connectors. On the left (driver's side) I unbolted the front drive shaft where it goes into the front diff. On the right (passenger side), I removed the exhaust brace (2 bolts in engine and 1 on the exhaust). Then with a LONG 1/2" extension stuck in the end of the offset wrench I was able to pop the upper ones loose. It was surprisingly easy considering what I've read on this thread! I consider myself lucky.

If anyone in the Colorado Springs area wants to borrow the offset wrench and thread chase and wants a hand, let me know. The # of beers owed is proportional to how badly they are seized :D
Thanks for sharing. Did you find any improvement in gas mileage?
 
#48 · (Edited)
Just did both air-fuel sensors and both O2 sensors on my 2008 today. I didn't find much in write-ups for this work so I figured it was either super easy and nobody needed it or not many have done it. Either way, here is what I did and a problem I ran into. Nothing earth shattering but maybe it will help someone considering doing on their own.

Symptoms leading up to the replacement: I was having some off idle hesitation up to about 2500 RPM or about 35MPH but it wasn't 100% of the time and nothing I tried could make it happen or make it stop. I posted a thread in the engine performance section about the issues I was having and got a lot of good advice. I cleaned the throttle body and bought a blue tooth OBD2 reader to get a better look at what was going on. I didn't have any codes but something wasn't right. After cleaning the throttle body (off engine) and taking a test drive with the OBD2 reader reporting on the Air/Fuel ratio commanded and the Air/Fuel ratio monitored nothing jumped out at me right away but I did notice that sometimes there was a pretty big Delta between the two and they were not really closely matched all the time. I was still running the OEM sensors and in the other thread had learned I was well past what was an expected life for all of them. I decided to go ahead and swap them all out in effort to restore the lost performance.

Specailty tools I used:
OBD2 Bluetooth
Torque Pro App
Lisle Dual Drive O2 offset wrench
Lisle O2 thread chase
I used Denso A/F ($108) and Denso O2 ($48) sensors from Rock Auto

Normal tools I used:
I didn’t keep a comprehensive list, I replaced all 4 sensors from underneath and I did use several 1/2" extensions with the Lisle wrench on the A/F sensors, 3' extension with U joint on the passenger side exhaust bracket upper 14mm bolts (from engine compartment), 14mm ratcheting box end on the driver’s side exhaust bracket upper bolts, 22mm box end wrench for the O2 sensors and 3/4" ratcheting box end wrench on the Lisle thread chase. The wiring harness plugs are set free by way of a standard screw driver with a narrow head and about a 3-4" length.

Drivers side A/F sensor:
The FSM alludes to removing a bracket with 3 bolts and by the picture in the FSM I wasn't sure what it was. Once under the driver’s side I saw what was in the way - a big bracket with two bolts on the engine block side and a single bolt on an exhaust coupling. Removing these bolts took a lot of effort and a cheater bar, which had either a bunch of torque from factory or had just taken a hard set over the years/miles.

Once the bracket was out of the way I was able to use a short/narrow standard screw driver to release the wiring harness from the sensor pig tail. I used the O2 wrench with 1/2" drive extension as a handle and a short cheater bar to get the A/F sensor to break free. Once the sensor was broken free it unscrewed by hand pretty easy. I ran the chase in/out the threads with little to no resistance. I coated the new Denso A/F sensor threads with their provided copper colored anti-seize and ran the sensor into the threads by hand until lightly seated. Once it was seated I used the Lisle O2 wrench to seat the sensor with a reasonable amount of torque.

Passenger side A/F sensor : The exhaust bracket was a PITA to remove. I could only reach the two upper bolts with a 3' extension and a U joint. Even then it took a cheater bar to pop each one free. The bottom bolt came out without issue. Getting the wiring harness free took the narrow standard screw driver but by the time I had my arm up where it needed to be I couldn’t see the plug so I had to do it by feel. Took me a couple tries to unplug the sensor. Removing the A/F took the Lisle O2 wrench but this time with a 3/8 socket wrench in the top side of the O2 wrench and a cheater bar on the socket wrench handle. Once it popped free, it was easy to un screw by hand. I ran the O2 thread chase in/out with little to no resistance, applied the copper color anti seize and installed the A/F sensor.

Drivers side O2 sensor : The sensor unplugs same as the A/F sensor with the short narrow standard screw driver. I used a 22mm 12 point box end to unscrew the sensor (the pig tail on the sensor fits through the box). The O2 sensor was tough to break free and just as tough to unscrew to remove. A couple times I stopped to make sure I wasn’t accidentally tightening it by accident. I even pondered if it might be reverse threaded for some reason. In the end it came out with a lot of effort. The threads on the old sensor looked like crap and I was worried it might have galled the threads and I was right. The threads in the exhaust pipe were in bad shape. It took a couple starts to get the O2 thread chase started square but once started I would turn it in about 1/4 turn and then back it off 1/2 turn or more and run it back in another 1/4. I pulled it out to clean and relube several times. It took a while but I eventually got the threads re-cut and cleaned up. I was able to install the new sensor with the copper anti seize without drama.

Passenger side O2 sensor: After all the drama on the driver’s side I was a little hesitant to pull this sensor out. I was able to unplug the pig tail and pop the sensor free without drama. This one unscrewed by hand once popped free and the thread chase ran in/out with little resistance. I coated the threads of the new sensor with the copper anti-seize and installed it by hand and set the final torque with the 22mm box end wrench before plugging the pig tail back in.

I re connected the negative side of the battery and started the FJ. It fired right up to a pretty fast idle, like it would on a very cold day (it was about 75F today). The initial idle seemed to have a little roughness to it but there were no apparent exhaust leaks or dash warning lights. I shut off the engine, plugged in the OBD2 scanner and started the engine. I ran through the scanner readings and everything seemed to be ok with no codes. I took a couple runs around the block and everything ran great. I took a longer test drive after cleaning up and its very noticeably better. Throttle response is back to what I remember and everything is smooth at idle. The initial idle roughness I felt at first start went away fast and everything settled in during this longer test drive.

I am really happy I bought the O2 thread chase! Both Lisle tools were great quality (forged) and I am pleased with both the pruchases. I almost skipped the chase but I would have been SOL today without it. I have no idea what happened with the threads in the drivers side O2 sensor, maybe I somehow messed it up while unscrewing it or maybe it got jacked up when it was installed on the assembly line. I'll probably never know but I am damn happy I had that thread chase and was able to recover from that situation.
This was the best O2 upstream bank 1 removal method that I found
FJ Cruiser P0031 O2 Bank 1 Upstream Sensor Best Tool and Method to Remove - YouTube
 
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#49 ·
This was the best O@ upstream bank 1 removal method that I found
FJ Cruiser P0031 O2 Bank 1 Upstream Sensor Best Tool and Method to Remove - YouTube
Love all the contributions to the thread! This is a great tool find. Im quickly approaching doing these all again this fall and will give this tool a shot I think (I admit i have a tool addiction).

Fwiw, I replaced my coils with densos from Rock Auto earlier this year and holy cow...241k mi and feels like new.

Y'all don't wait for CEL, if it ever happens at all you're probably 50-100k overdue.
Still never seen a CEL on this thing. Preventative maintenence the only way.

Thank you everyone for making your contributions and improving this thread with the collective knowledge and lessons learned. Love it!
 
#53 ·
Just did both air-fuel sensors and both O2 sensors on my 2008 today. I didn't find much in write-ups for this work so I figured it was either super easy and nobody needed it or not many have done it. Either way, here is what I did and a problem I ran into. Nothing earth shattering but maybe it will help someone considering doing on their own.

Symptoms leading up to the replacement: I was having some off idle hesitation up to about 2500 RPM or about 35MPH but it wasn't 100% of the time and nothing I tried could make it happen or make it stop. I posted a thread in the engine performance section about the issues I was having and got a lot of good advice. I cleaned the throttle body and bought a blue tooth OBD2 reader to get a better look at what was going on. I didn't have any codes but something wasn't right. After cleaning the throttle body (off engine) and taking a test drive with the OBD2 reader reporting on the Air/Fuel ratio commanded and the Air/Fuel ratio monitored nothing jumped out at me right away but I did notice that sometimes there was a pretty big Delta between the two and they were not really closely matched all the time. I was still running the OEM sensors and in the other thread had learned I was well past what was an expected life for all of them. I decided to go ahead and swap them all out in effort to restore the lost performance.

Specailty tools I used:
OBD2 Bluetooth
Torque Pro App
Lisle Dual Drive O2 offset wrench
Lisle O2 thread chase
I used Denso A/F ($108) and Denso O2 ($48) sensors from Rock Auto

Normal tools I used:
I didn’t keep a comprehensive list, I replaced all 4 sensors from underneath and I did use several 1/2" extensions with the Lisle wrench on the A/F sensors, 3' extension with U joint on the passenger side exhaust bracket upper 14mm bolts (from engine compartment), 14mm ratcheting box end on the driver’s side exhaust bracket upper bolts, 22mm box end wrench for the O2 sensors and 3/4" ratcheting box end wrench on the Lisle thread chase. The wiring harness plugs are set free by way of a standard screw driver with a narrow head and about a 3-4" length.

Drivers side A/F sensor:
The FSM alludes to removing a bracket with 3 bolts and by the picture in the FSM I wasn't sure what it was. Once under the driver’s side I saw what was in the way - a big bracket with two bolts on the engine block side and a single bolt on an exhaust coupling. Removing these bolts took a lot of effort and a cheater bar, which had either a bunch of torque from factory or had just taken a hard set over the years/miles.

Once the bracket was out of the way I was able to use a short/narrow standard screw driver to release the wiring harness from the sensor pig tail. I used the O2 wrench with 1/2" drive extension as a handle and a short cheater bar to get the A/F sensor to break free. Once the sensor was broken free it unscrewed by hand pretty easy. I ran the chase in/out the threads with little to no resistance. I coated the new Denso A/F sensor threads with their provided copper colored anti-seize and ran the sensor into the threads by hand until lightly seated. Once it was seated I used the Lisle O2 wrench to seat the sensor with a reasonable amount of torque.

Passenger side A/F sensor : The exhaust bracket was a PITA to remove. I could only reach the two upper bolts with a 3' extension and a U joint. Even then it took a cheater bar to pop each one free. The bottom bolt came out without issue. Getting the wiring harness free took the narrow standard screw driver but by the time I had my arm up where it needed to be I couldn’t see the plug so I had to do it by feel. Took me a couple tries to unplug the sensor. Removing the A/F took the Lisle O2 wrench but this time with a 3/8 socket wrench in the top side of the O2 wrench and a cheater bar on the socket wrench handle. Once it popped free, it was easy to un screw by hand. I ran the O2 thread chase in/out with little to no resistance, applied the copper color anti seize and installed the A/F sensor.

Drivers side O2 sensor : The sensor unplugs same as the A/F sensor with the short narrow standard screw driver. I used a 22mm 12 point box end to unscrew the sensor (the pig tail on the sensor fits through the box). The O2 sensor was tough to break free and just as tough to unscrew to remove. A couple times I stopped to make sure I wasn’t accidentally tightening it by accident. I even pondered if it might be reverse threaded for some reason. In the end it came out with a lot of effort. The threads on the old sensor looked like crap and I was worried it might have galled the threads and I was right. The threads in the exhaust pipe were in bad shape. It took a couple starts to get the O2 thread chase started square but once started I would turn it in about 1/4 turn and then back it off 1/2 turn or more and run it back in another 1/4. I pulled it out to clean and relube several times. It took a while but I eventually got the threads re-cut and cleaned up. I was able to install the new sensor with the copper anti seize without drama.

Passenger side O2 sensor: After all the drama on the driver’s side I was a little hesitant to pull this sensor out. I was able to unplug the pig tail and pop the sensor free without drama. This one unscrewed by hand once popped free and the thread chase ran in/out with little resistance. I coated the threads of the new sensor with the copper anti-seize and installed it by hand and set the final torque with the 22mm box end wrench before plugging the pig tail back in.

I re connected the negative side of the battery and started the FJ. It fired right up to a pretty fast idle, like it would on a very cold day (it was about 75F today). The initial idle seemed to have a little roughness to it but there were no apparent exhaust leaks or dash warning lights. I shut off the engine, plugged in the OBD2 scanner and started the engine. I ran through the scanner readings and everything seemed to be ok with no codes. I took a couple runs around the block and everything ran great. I took a longer test drive after cleaning up and its very noticeably better. Throttle response is back to what I remember and everything is smooth at idle. The initial idle roughness I felt at first start went away fast and everything settled in during this longer test drive.

I am really happy I bought the O2 thread chase! Both Lisle tools were great quality (forged) and I am pleased with both the pruchases. I almost skipped the chase but I would have been SOL today without it. I have no idea what happened with the threads in the drivers side O2 sensor, maybe I somehow messed it up while unscrewing it or maybe it got jacked up when it was installed on the assembly line. I'll probably never know but I am damn happy I had that thread chase and was able to recover from that situation.
Old thread, sorry. How did you disconnect the pigtails from the harness with a screwdriver? Not sure exactly where to insert and seemingly with one hand at arms length.
 
#54 ·
What you do is push the little tab that is snapped over a detent on the mating part, down so it is levered off the detent, and then you use the small screwdriver blade to pry the two halves apart. The seal is waterproof so you must push against the drag from that seal. Just make sure the tab is pushed down so its not hooked on the detent and the lever action from the little screwdriver will push the two halves apart.
 
#59 ·
Kind of interesting that Rock Auto lists two Denso O2 models for the '07, but only one for the '09, though I believe the difference is just the wire length?:

Font Screenshot Parallel Rectangle Number


But I believe these are what I should order? It's a single P/N for the O2s and a single P/N for the A/F?

@ROMAD if you ever come to central Mexico I owe you a dinner. Between this and the UDR fuel pump replacement thread you made, you've made my life immensely easier troubleshooting the lean issues I've recently been having!
 
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