Nice DIY; the only thing I would add is that my hands are too big to get to the connector from above. I used this grappler gizmo ($15 @ Home Depot) from underneath.
Clip the hooks around the sensor side of the connector, reach up with one hand to open the tab and jiggle the tool with the other hand to loosen the plug; you can tell when success is at hand when the tab doesn't click back down when you let go. You can then reach up and pull out the plug.
Sir ..Just changed my air fuel sensor,on bank1..the hard one for unclipping the socket.. simple two guys ...one guy holding the locking clip down....the guy underneath unplug it ....took a 10 minutes to do it..... very easy
Last night I replace the bank 1 sensor 1 (between the firewall and motor) on my 2002 RX300. It took me about 15 minutes.
First, I was able to buy the Denso 234-9009 Air/Fuel Sensor from Amazon for 119.76 and free two day shipping. Worked out great.
This is what I did. I jacked the car up on the passenger side and put a jack stand under it (make sure you put the emergency brake on). I had driven the car about 30 minutes prior so the exhaust pipe was warm but not hot. I got under the car, located the sensor and sprayed PB blaster on it to loosen it up.
Next, from under the hood, I located the plug on the back firewall. Just look dead center on the back firewall. There is an small opening for just one hand to fit in between the intake and the firewall.
Just put your hand down in there (it's a tight fit and you'll need a shop light) and you'll see the plug. Here's the thing. You can only get one hand in that small area so the only thing you can do is try to push the tab down with your thumb. If you could get two hands in there, you would be able to push the tab down and pull the other side to unplug it. I don't see how there is any way to do that. Just not enough room.
Anyway, the tab on the plug was stiff but I could feel a little movement, so I asked my 17 year old son to try and push the tab down while I got underneath the car to pull the plug out. That didn't work.
Well, I got out from under the car to study the plug again under the hood. This time, I reached in and got my thumb on the tab and pushed down as hard as I could until I heard a definite click noise. When this happened, I noticed that the tab was now locked down. I didn't need any special tool, just a strong thumb. I pretty sure that Lexus designed the tab to be pushed until it clicks. Once you do that you can simply get under the car and pull the plug out. Easy as pie.
On to the sensor...I used the 7/8 O2 sensor socket and a breaker bar. The socket cost me 10 bucks at the parts store. Mine wasn't on that tight. I probably just could of used a normal swivel head ratchet to break it loose. I didn't need a curved wrench or any special tool to back out the sensor. Once the sensor was a little loose, I took the socket off the ratchet and used the socket with my hand to manually back out the sensor. This took all of one minute and out came the sensor.
When I reintalled, I spread the anti-seize grease on to the threads and put it back in the hole in the exhaust. I tighten it up (but not too tight), plugged in sensor (you hear a snap when you plug it back in) and it was all done.
The last thing was to pull out the EFI fuse to reset the check engine light. I removed it for about 30 second, then reinstalled it. When I started the car, the check engine light went off and I felt good about it.
In conclusion, this was not a hard job (at least for me anyway). The only thing is that plug. If you push that tab down hard enough with your thumb you should heard that click noise indicating that the tab is down and in release mode. If you get that, your golden.
To reset the CEL, pull the ECU fuse from the engine compartment for about 10 minutes. You can actually do this at the start of the work.
I pull out the yellow 20 amp EFI fuse, the one next to the 7.5 amp ECU fuse. I'm not sure if I'm right or your right. I just heard it was the EFI fuse that needed to be pulled to reset the Check Engine Light.
Thank you, 81corolla. Your post saved me about $500 on repairs. I have an ES300 (1999) and could not pass emission test (IL). The trouble code is P1133. It is related to the Bank 1 Sensor 1 and Midas wanted $700 to replace both Bank 1 Sensor 1 & 2. I purchased an OEM air / fuel sensor from ebay at $142 and it only took me less than 20 minutes to get the job done. Mine is not RX but your detailed post was very helpful. Thanks again and all the best!!
Look down between the radiator and engine and you will see it sticking out of the front exhaust manifold. The darn electrical connector can be a little annoying to disconnect. A 7/8" open end wrench will take car of the sensor.