Denso 234-9021 Upstream Heated Oxygen Sensor with 4-Wire Plug and 14.17†Harness

First off, technically, this is a Air/Fuel sensor, NOT a O2 sensor. If you do your research you'll know they are not the same as some may say. They work differently and are not interchangeable. They even look different. Air/fuel sensors have less holes in the sensor end compared to O2 sensors. They are made differently with A/F having more rare earth material--hence quite a bit more expensive too. Always, Always go with factory OEM parts on A/F sensors because different car brands have specific voltage or current requirements for your vehicle and will not cure a sensor problem if not in the correct operating range. You'll be sorry if you don't go OEM. I replaced 2 of these A/F sensors on my V-6 3.0l--one each on each exhaust manifold, and a O2 sensor aft of the catalytic converter. Runs great! Fuel trims are spot on. Original Denso sensors lasted 180,000. I bought the car from a friend who had never had to change them. So Denso was my choice for replacement!

Product was well packaged and arrived ontime. I like the fact that Amazon forces you to verify if part is the right fit for the vehicle is a nice feature., so you won't order wrong part.I bought this product to fix the issue causing P1135 on my 2001 Sienna. I read the code and found out that Bank1 sensor 1 is bad (underneath steering column and hard to get to). I had a mechanic put in this part for me. No issues fitting the product in.I took the vehicle for emissions too soon after the installation. For the vehcicle to be testable, it needs have all monitors set to READY status. I had two of them not ready since the mechanic erased them all. Hence the vehicle was rejected. I waited for few more days before taking it again for emissions and it passed this time. FOR INFO: Note that I still have one of the systems monitor status set to "not ready". For 2001 model years onwards, you can have 1 system not ready and still pass the emissions if no other DTC or MIL exists. For 2000 and below years, 2 monitors can be not ready and still pass the test. (this is in IL)Overall with some googling and having some idea about vehicles, it saved me some $$$ to do dianose, buy the part and have it fixed myself. If I had to take it a mechanic for full service, the quotation I was given was $260+tax+Labor.

I have a 2002 Toyota Avalon XLS. This was the exact replacement and it solved the P1135 code issue. My engine check and VSC lights came on. It was not caused from a bad or loose gas cap (which can also be the cause), so I went to Auto Zone and they checked the code for free with a code reader.The error code was P1135 for Bank 1 Sensor 1 Air Fuel Ratio Sensor. Of course, this is the most difficult sensor to reach (arrg!). It is in the exhaust manifold on the back side of the engine just in front of the firewall. You can only really reach it with one arm by coming in from the top of the engine on the driver's side down by the firewall. I could not reach it from under the car, there was no space for my arm to go in and do anything. You can see it from underneath, but that's about all.I ordered this part after verifying it was the correct one, along with the 02 sensor socket recommended (you really need to buy this!). I already had the PB spray. The hardest part was gaining access to get good leverage on the sensor with the wrench. I sprayed the old sensor with the PB spray a few times during the week letting it soak in. Once I got some leverage on the socket with the ratchet, the old sensor broke free. You have to get your body on top of the engine and use your body weight to push down on the ratchet with your arm. Once it broke loose I could then remove the old sensor with my fingers. Then next challenge was to unplug the electrical connector using only one hand. I sprayed WD40 on the connector which helped it come apart easier. FYI - you SQUEEZE the tab on the connector to unlock it.Once the old sensor was out, I sprayed the manifold hole with WD40, cleaned the threads with a toothbrush, then wiped the hole and area clean with a rag (you do most of this by feel only). The new Denso sensor comes with a small tube of anti-seize. It's more than enough, you could do 4 more with this. Put the anti-seize on the threads being careful not to get any on the sensor body.Replacement took only about 5 minutes, the new sensor screwed in perfectly to hand-tight then using the 02 socket it was easy to tighten fully. The connection of the new electrical cable is easy to do with one hand once you have the old one off because it simply clicks right together. Again, you have to do it by feel only.This saved me over $300 from going to the dealer and about $250 from having an aftermarket shop doing it. Patience and using lots of penetrating oil is the key!!!

Installed both air/fuel Denso #234-9021 sensors on our 2000 ES 300; banks 1 and 2. Very easy to remove with an 7/8's open end wrench (22 millimeter is also good) after applying penetrant and warming the engine about two minutes. Bank 1 between engine and firewall was not as easy, but broke free with slight tap. These sensors were replaced after 166,000 miles as normal maintenance to avoid "engine light" problems some have experienced. The under vehicle 02 sensor will be soon replaced as required. One prior complaint was against using fuel additive which may have caused sensor failure. Have used "Lucas" fuel and oil additives regularly-no problems. This engine will build sludge and carbon easily and fuel additive and regular oil changes with additive (3 to 4,000 miles) do help. The Valvoline high mileage synthetic is an excellent product. Would have given sensors five stars if packaging had been a box instead of envelope. First mailing in envelope through UPS resulted in one sensor being crushed and had to be returned. If envelopes are used they should be marked "FRAGILE" since sensors should not be dropped or crushed. New sensors are responding well as designed for this engine.Received an undamaged replacement (in an envelope). Have now driven car several times and sensors are responding well; no problems. I seem to sense a little more power on hills than before. Remains to see if fuel mileage improves.