I'm changing the front O2 sensor on my '96 3.4 manual 4WD. I can't tell where the wiring harness plug is. I see the O2 sensor and try to follow the wire up to the harness, but it leads to somewhere above the transmission/transfer case and can't see where it ends or even get my hand up there. I'm looking at the writeup on 4runners.org but can't tell where it is from the pic. Can anyone help me with this?

 

well I found this picture from the interweb:


that's definitely not what mine looks like. The wire is much longer on mine and leads to up above the transmission. I can kind of see where the connector ends, but there's no way I can get my hand up there and I have tiny hands. What gives? Please don't tell me I have to drop the transmission just to change an O2 sensor.

 

you get to the plug by going inside the vehicle and taking apart
the console till you can find the plug on top of yer tranny


yer picture is what automatic transmission owners have for plugs. down low

manual is way up on top

 

I realized maybe I need to go through the top but didn't get around to trying it. The nuts that hold the sensor to the exhaust are stripped or something. It's a 12mm nut right?

 

12mm yes. the nuts don't really strip as much as they peel apart like a flaky pastry.
...the outside layers corrode slowly away,
leaving a nubbin. a small pair of baby vice grips should be able to twist them off

the studs underneath do not corrode (at least mine didn't)


in the pic in this thread, that person definitely doesn't (a) put a lot of miles in or (b) drive in salty snowbanks
because (c) mine at 130,000 miles looked like 2 raisins on a post. as soon as I hit them with the 12mm they turned
into 11mm rounded nuts. tiny 4 inch vice grips got them off with no hassle

you will need new nuts from the dealer...about 4 bucks. other nuts will end up seizing on there and then you will need a whole new pipe.


when you put the new ones on crank them pretty tight. them check them in 2 weeks. I kinda
sorta tightened mine and in 2 weeks while I was under there looking at something else I found they
loosened a bit, so I really whopped them with a small 12mm and now they are on good.

 

Edzo, thanks for the advice. I'll go ahead and get a couple new nuts from the dealer and hopefully take another crack at it this weekend.

 

don't forget a special toyota o2 gasket also. some reason they work better than
gaskets you buy elsewhere

 

The o2 sensor I bought came with a gasket. That should be the right one, no? I bought my sensor from URD.

 

toyota dealer gasket is paper with metal surround. almost looks cheap

one side has more paper than the other side. this more-paper side
faces up towards the sensor.

I don't know if you have the same gasket. I mean it should work,
but only one gasket and one sensor is designed to mate 100% with
the flange. so if you end up with leaks....

a dealer sensor has a very slight
rounding off, it isn't 100% flat. when bolted on it makes a tight seal.

I once tried a non-dealer part and the flange was too flat, so when I
cranked it down, it ended up leaking

who knows what URD sold you ? is it a two piece screw in sensor with
a flange ? then if it is, it is not a stock sensor. I would use the gasket
URD provided. toyota stock sensors are pressed into the flange and
cannot be removed, it is a one piece.

anyway crank the hell out of it. I imagine it's fine

 

Yes, that is the correct one.
The gasket will be the same one you get from the dealer.

 

The O2 sensors URD offeres are the same sensors you buy from the Toyota dealer. The only difference is ours come in a pretty Denso box, the the same sensor from the Toyota dealer comes in a drab brown Toyota box.

Gadget

 

um wouldnt the codes indicate O2 issues??

 

yes I had a CEL and when I checked the code it indicated a bad O2 sensor.

The second time around was pretty easy. Used vice grips to get the nuts off of the O2 sensor and went through the shift boot to get to the harness connection. Took a little fishing around to get the connector to where I could get my paws on it but all in all a pretty straightforward procedure. Why is everything always 10x easier the second time around?

 

I always hear people replacing the front O2 sensor but not the rear one. Why? Which O2 sensor brand is best?