This is a guide on how i changed my 2 upstream Oxygen (o2) Sensors
I thought maybe some other people may find this helpful
NOTE: most of the images can be enlarged by clicking on them. if you need bigger ones then message me or comment below.
Upstream means the oxygen (o2) sensors before the catalytic converters there are 2 upstream and 2 downstream (after the catalytic converters)
This was done on a 2000 Nissan Pathfinder LE 4 wheel drive.
I changed my sensors because i got a Serve engine soon light because of the sensors, and i noticed my fuel consumption was getting really bad.
I got my oxygen sensors from Autozone for about $60 a sensor. They are bosh (same ones the dealer used) and half the price of the dealership that told be about $120 per sensor. Since there are 4 o2 sensors you need to ask for the right and left upstream o2 sensors.
I used the "exact fit" because you can buy universal o2 sensor but you will splice the wires and i'm not that great with electrical stuff. also the exact fit will have the clips in the correct places making it easy and keeping wires away from hot parts.
here is a diagram showing the sensors and part numbers (dealership part numbers) if you would rather get them from the dealership and not autozone (but like i previously noted they are the same, just more expensive).
Here are the tools i used.
You will need a special socket to remove the o2 sensor. I bought mine at harbor freight on sale for 5.99 (regular price 7.99)
Using this long one i did not have to remove any heat shields. This tool is required for the job
3/8in. DRIVE RATCHET. this tool is required for the job.
The 2 extensions are helpful but i found later that they are not vital. if you do use the extensions then you will need 1 universal joint.
the hammer and flat head were used to break the clips that hold the original wires in place and keep them from hot surfaces.
This is what the new sensor looks like. the other one looks the same, just a longer cord and has 2 clips.
First start off by unplugging the negative terminal of your battery. this is recommended whenever dealing with electricity.
Next, find the first sensor. located on the passenger side in between the 2 heat shields near the fire wall. Shown here
Follow the wire to the clip, break the plastic clip off so that you can get the wire free from the plate.
the arrow on the right shows where the clip will be in and one arrow on the right shows the clip broken off tooth but on the sensor wire. I simply put the flat head on the plastic tooth that grips the metal and hit it with the hammer to break it off.
Now follow the wire to the plug and unplug it.
here shows the location of the sensor plug
to unplug the sensor, there is a tab on the bottom you have to depress then at the same time pull
Now put the o2 socket on the sensor, make sure your all the way on the sensor, it may require a bit of giggling the socket to get it to sit properly on the sensor. Now i used my extensions and universal joint to unscrew the sensor (once the socket was on securely i felt my way down and attached the universal joint, then the extension, then the drive). I later found out that the drive fits in there and i did not need to use the extensions at all.
This is what my old one looked like
This is the new sensor, showing that it already comes with anti-seize already on it. if you buy another brand, then check to see if they too put some on. if not then put on a little around the thread so that next removal will be easier.
now hand screw in the new sensor, put on the socket, and tighten to 20 ft/lbf if you have a torque wrench, or just get it tight using the drive but not overdoing it.
follow the wire in the original path the previous sensor had and clip in that plate.
plug in the sensor into it's plug, and that's one done!
The second sensor is located on the drivers side near the firewall the sensor is shown in the red oval. it's under the break fluid reservoir.
The procedure here is the same as the last sensor,
follow the wire, break off the clips (there will be 2 on this one, one half way up from the sensor and the break fluid reservoir. and another located on top of the engine nearly in between the passenger side and driver side.)
unplug the plug, shown in the picture below. my wire was blue, so it was easy to follow
now the part i wish someone told me!
to get to the sensor the easiest way is to sick your hand down the right side by the shock. shown in the picture below.
If you stick you hand down there, you will have amazing acces and no hoses in the way.
so get the socket on securely on the sensor.
then send the drive down there and clip on and unscrew the sensor. yes, it fits heres a pic.
now you will have to be careful and move some of the hoses around so you can fit in you hand and break the sensor free.
once it was broken free, i detached the drive and unscrewed the sensor by hand using the sensor socket.
here is the old one removed
Now putting the new one in, i hand screwed in the new sensor, then put on the socket, gave it another turn till i could no more, then sent down the drive, attached it, and it should be tightened to 20 ft/lbs, but i don't have a torque wrench so i got it tight with out overdoing it.
then follow the wire back to the plug remembering to get in the 2 clips to where the previous ones were.
then remember to connect back your negative terminal of your battery and your done!
here is one more picture showing the clip bent up. the clips bend up and down easy, so when you go to unclip it i recommend bending it up first then unclip it. when going to clip it, i would connect the two ends first then slide the connector from the sensor on the metal bar, finally bending it back down.
overall it took me about an hour and a half to do this, so it should go faster now that you know where to put your hands and instead of trying to get crazy extensions to unscrew them, just use the plane old drive and it will speed up the process.
Finally, this is a showing how i replaced my oxygen sensors, you may run into unexpected problems and your results may vary, if you break something it's not my fault.
Cheers, skiski329