Review on 🔌 Denso 234-9021 Upstream Heated Oxygen Sensor: Advanced 4-Wire Plug with 14.17” Harness by Dan West

I have a 2002 Toyota Avalon XLS. This was an exact replacement and solved the problem with code P1135. My check engine and VSC lights came on. It wasn't caused by a bad or loose gas cap (which could also be the cause) so I went to Auto Zone and they checked the code with a code reader for free. The trouble code was P1135 for Bank 1 Air Fuel Sensor 1st ratio sensor. This is of course the most inaccessible sensor (arrg!). It is located in the exhaust manifold at the rear of the engine just in front of the bulkhead. You can really reach it with just one hand by going down through the firewall from the top of the engine on the driver's side. I couldn't reach it under the car, there was no room for my hand to do anything. You can see it from below but that's it. I ordered this part after making sure it was correct, along with the recommended 02 sensor socket (you really need to buy this!). I already had the PB spray. The hardest part was accessing the sensor with a wrench. I sprayed the old sensor with PB spray several times over the course of a week and let it sit. As soon as I pressed the socket with a ratchet, the old sensor came loose. You need to put your body on top of the motor and push the ratchet with your hand using your body weight. Once it came loose I was able to remove the old sensor with my fingers. The next task was to disconnect the electrical connector with one hand. I sprayed WD40 on the connector to make it easier to loosen. FYI - you press the tab on the connector to unlock it. Once the old sensor was out, I sprayed the manifold bore with WD40, cleaned the threads with a toothbrush, and then rubbed the bore and area clean with a rag (most of this you do by touch). A new Denso sensor comes with a small tube of anti-seize. That's more than enough, you can make 4 more with it. Apply anti-seize to the threads, being careful not to get it on the sensor body. The replacement only took about 5 minutes, the new sensor was screwed in perfectly all the way, then it was easy to tighten completely with the help of bushing 02. Connecting a new electrical cable is easy with one hand after removing the old cable as it simply snaps into place. Again, you should only feel that way. It saved me over $300 on a trip to the dealer and about $250 at an aftermarket shop. The main thing is patience and the use of a large amount of penetrating oil!