Denso 234-4233 Downstream Oxygen Sensor for Toyota 1.8L with 4-Wire 21” Harness

Solved my gas mileage issues. Great quality item

This product worked perfectly for solving my emissions related error codes on my 2003 Toyota Corolla LE (manual). This product is the downstream O2 sensor located under the car (below the passengers side door) below the catalytic converter. My check engine light appeared so I had the car inspected by 2 mechanics who pulled the error codes with their OBDII scanner. I had the dreaded P0420 code (cat converter) plus 3 others related to the evap system P0440, P0441 and P0446. They both said I need a new cat converter and evap canister. The parts alone are approx. $1,200-$1,400 for the factory catalytic converter and about $385 for the canister plus labor. So probably around $2,700-$3,000 for parts and labor. I did a lot of research online, watched youtube videos etc to find that Toyota Corollas notoriously throw these codes for emissions. Sometimes replacing the gas cap alone will clear all of your codes so do the folling steps in this order if your Toyota is throwing these emission codes. 1. Make sure you have a factory gas cap (very important) always turn gas cap until it clicks, never overfill gas tank or top off the gas tank, it will ruin the evap canister. Stop pumping gas when the pump automatically stops 2. replace both upstream and downstream O2 sensors, Denso makes the best non factory part at a great price. The sensors come with a small tube of Anti sieze lubricant which you must use on the threads, do not substitute with brake grease or other lubricant. Unplug all emissions related parts including both O2 sensor and egr sensor, spray all electrical contacts with electric parts cleaner and reconnect. I also purchased a 7/8" O2 sensor socket adapter which really helps out, access is tough with a regular wrench and it's cheap to buy. Usually appears in the Amazon 'customers who bought this also purchased...' message when you buy the O2 sensors. Once both O2 sensors have been installed, you'll need to reset your error codes and then drive the car for approx. 20 miles to see if they reappear. You can have AutoZone read ODBII codes and reset OBDII codes for free. I bought an app for android phone called 'Torque Pro' (4.99) and a bluetooth adapter for my OBDII port ($14.99 on Amazon) to read and clear my own codes. OBDII scanners are usually $100-$140 from auto retailers. In conclusion, after worrying about these issues for about 8 months, I installed 2 new O2 sensors and a new factory gas cap, cleared the error codes and passed my emissions test with flying colors saving myself about $2,800. I highly recommend trying this first before replacing the cat converter and/or evap canister.

I have a 2003 Corolla LE and I have had a lot of problems with the P0420 Catalyst system efficiency below threshold bank 1 code over the years and after it recently came up I bought this to try to fix it. I replaced the oxygen sensor with another one from amazon (Sold by "TheBigDeals") a few days before buying this one which did not get rid of the check engine light or code. I researched some more and found out that that might be because I needed to use an OEM sensor. This OEM Denso sensor worked, and I have no check engine light AND PASSED MY SMOG TEST! I am so happy that I don't have to replace the catalytic converter, which can be around a thousand dollar + repair.In case it might help you, if you have a 2003 or 2004 corolla and this doesn't work for you, I found that there is also a Technical Service Bulletin from Toyota issued on a repair that they can do for this problem which calls to "reflash" the computer in the car and costs about $100. It seems to have helped some people and I am going to get it done now as a preventative measure even though I passed smog. Here is specifically what it is. https://www.discountconverter.com/tech-tips/news_page.cfm?Key=catalytic_converter-&News=228http://tsb.deccats.com/TSB-3290-corolla-03-04.pdfOther common causes of the p0420 code from what I researched are an exhaust leak, a dirty Mass air flow sensor (see "walaxvw"'s answer here http://www.fixya.com/cars/t1056719-p0420_code_toyota_corolla) and I also read "fouled plugs, dirty injectors, or excessive carbon deposits in the combustion chambers."Also I tried Redline Fuel Cleaner, Guaranteed to Pass, Cataclean, and Seafoam, and the codes and check engine light persisted until I changed the (downstream) oxygen sensor to this OEM Denso one.

Ease of installation

Denso is the OEM maker, so it fit perfectly, 2nd time changing them, but to be fair the car is over 220k miles, so hard to ask for more than that!

Same part the factory installed at a fraction of the cost

I purchased this as a potential quick and MUCH cheaper fix to the dreaded P0420 code on a 2003 Toyota Corolla that has approximately 128,000 miles on it. I have heard many differing opinions on how often changing this oxygen sensor actually will fix the issue. I figured if I did end up replacing the CAT, then I would replace the oxygen sensors any way so what the heck. Why not try with the least expensive part first.I have driven about 250 miles now and I checked the status of the Catalytic system with my code reader and it has indeed run and evidently passed the last time it ran. The light had previously been lit almost continuously for the last year or so. I am not overly optimistic as I am guessing my cat system has indeed decreased in efficiency but hopefully this will buy me another year or two.Also, I did do a few other preventative maintenance items at the nearly same time, so if you have the same year corolla and are looking to try and get rid of the light, I did the following.At roughly the same time I popped in the new oxygen sensor, I replaced my spark plugs with NGK IRIDIUM'sShortly after, I also drain/filled my transmission fluid, drain/filled my coolant, changed oil to a semi synthetic. These three items I did after I am fairly certain the code was fixed so I don't know if they have any impact on anything or not.If the light comes back on, I will try to remember to update this review for those of you that are experiencing the same frustrating issue and don't want to spend $$$$ for a new factory CAT.

We bought this and continued to have issues. Our friend pulled a code that said this sensor is defective. They also gave zero customer service. Buyer beware.