couple of q's.
1. the repair manual says "loosen nuts" to remove 02 sensor. mine are too rusted to determine if they are normal hex-nuts or possibly something else (a square nut, perhaps?). also, does anyone know what size nuts they are?
2. i have no plug showing from underneath. the wire goes into the bottom side of the truck through a piece of rubber that i am unable to remove. i'm assuming the plug is just on the other side of this. any suggestions?
3. after i get the new 02 sensor in, do i have to have it recalibrated or anything like that? or is it just a r&r and go? i'm not sure how the computer works with the sensor and whatnot.
4. should i bother being optimistic about gaining a few mpg's?

thanks

 

no one has any suggestions for me on how to get this thing off?

i found out where the plug is. believe it or not, it's underneath the driver's seat. i don't know why. i also found a little black box with a red LED on it underneath that seat that i never noticed before. at first, i thought it was a bomb. but then i thought, well THAT doesn't make any sense. the light isn't blinking, and i don't hear any ticking. so it's not a bomb. so then i thought it's a tracking device. but then i noticed that it says toyota on it. so i'm stuck with not having a clue as to what this box is.

 

Heres a bump for you. I cant get my O2 sensor off either.

What the heck is under your Seat ? Maybe its the Toyota Black Box ?

 

mine were a regular hex nut...10mm IIRC (might be remembering incorrectly, though). mine where also quite rusted and i thought the same thing when i first looked at them. but, after scraping away the rust, they turned out to be regular nuts.

i did not have to replace mine...in my case, one of the studs had broken off, my O2 sensor was loose, so i took replaced the studs with bolts and nuts, but did not have to disconnect the wires, so i can't really help there...sorry.

might be a good idea to reset the ECU by disconnecting the battery for 20 minutes or so (might actually not take that long, but it does take a little while...i've heard some people say that you should leave it disconnected overnight, but the consensus from what i have read seems to be 20 minutes).

my understanding is that the ECU sort of "learns" as it goes along...and will "learn" the wrong things from a bad O2 sensor, so you want to reset it to it's base programming so it can start from scratch again. you don't have to, but it will take the ECU longer to "re-learn" if you don't.

(at least that's how it worked on my old acura...i think the yota set up works the same way.)

bad O2 sensors can definitely have an impact on MPG, so, if your old one was bad (did you get a check engine code for it or test it before replacing it?), i would say there is a good chance you will see some improvement.

 

no, i didn't get a check engine light. i just got on a full tune-up kick for all my vehicles and o2 sensors were on my list because i have never changed them before. the one on my car was cake. just had to remove a little plate that was in the way and then it was no problem. the 4 runner is a different story. real easy to get to, and as of yet, impossible to remove.

 

i dunno really. i'm gonna have to remove the seat to find out. i'm thinking it MIGHT have something to do with the alarm that my truck "supposedly" has. (i have some alarm switches up by the ash tray but it has never worked). when the alarm goes off, it only blinks the lights. there's no horn. so, if it's not something to do with the alarm, then i have no clue what it is.

 

If the nuts are too badly rusted to remove, just cut or grind them off and replace them with some new bolts. I did that on my '85, using a pair of stainless steel bolts, nuts and lock washers.

 

how are the bolts attached? i was under the impression that there were a couple of threaded rods that are welded to the flange in the exhaust pipe. then the o2 sensor flange/gasket slipped over the bolts, then the nuts held it on. if this is correct, then if i cut the bolts off, how am i supposed to get new ones on? if this is incorrect, then by all means, please correct me.

 

I think my stock manifold had separate bolts, but it was about 6 years ago I swapped to a header so I do't remember for sure. My header does use bolts and I think those bolts came off the stock manifold. If they are studs, then a nut breaker would get the nuts off, then use new nuts on the studs. If the studs are not useable either remove and replace them or drill them out and use bolts.

 

on mine, the studs were screwed into the flange, not welded. i was able to unscrew one with vice grips. the other i had to drill out. then i replaced them with bolts.

 

That may have been the case with my old manifold as well. The original one was warped and had a new one installed. Maybe it was easier for the shop to stick bolts in there than mess with pulling the old studs. I like the s/s bolts, use a little anti-sieze on them and they will come off when needed. I use that same combo on all my exhaust bolts.

 

I need some help here guys. I'm also wanting to replace my O2 sensor but the nuts holding the sensor in place has frozen with rust. Do I just cut them off and replace with bolts as others have suggested? If so, how do the bolts go on? Do I have to tap new threads?

Troy

 

bump..

 

Not familiar with how that engine/sensor is installed. But if there are separate bolts and nuts, just get them off however (cut, grind, break) and replace them with something new. I used some 1/4" s/s nuts and bolts for my 22RE sensor (aftermarket header). If the bolts go into the manifold, then try repeated soaking with a good penetrating oil (PB Blaster, Kroil, etc. not WD40). Hit the bolts with a propane torch and also try an impact driver to see if you can break them loose. If you can't get them out, then drilling/tapping will likely be needed.

Whatever approach you end up using, be *sure* to use some anti-sieze on the new hardware you use to reinstall the new sensor. That'll make future removals so much easier.

 

Thanks Roger,

I'm sure there are plenty of others who have run into this problem. I'm now thinking about trying a nut splitter first, and if that fails, I'll cut them out.

Troy

 

My brother and I tried for hours last weekend to remove the nuts for my rear o2 sensor and couldn't get them off. We did everything we could think of, but it was pretty much impossible considering the nuts were rusted to almost nothing and it was such a tight space. I figured I would have to take it somewhere, but finally we found this and it saved our butts:

IRWIN Bolt Grip Fastener Remover

Worked great. Nuts came off right away. Absolutely worth the money in my opinion.