Review on Denso 234 9056 Fuel Ratio Sensor by Andy Metzger

This sensor has a 'ring' or 'collar' around it that requires a thin wall sensor socket. I used "CTA Tools 2064 Thin Wall Oxygen Sensor Socket" B005OH0ITM. It was still difficult to remove without moving the inverter. I was able to get it underneath after removing all the stuff in and around the hood wipers. I used a liquid key and started the car to warm up the manifold. It still took two people, one upstairs, the other downstairs, to get this sucker moving. Sensor is a trademark. It might even be an OEM. Avoid cheap sensors from strange brands. You don't want to repeat this repair. For my 2005 2nd generation Prius: This is not an oxygen sensor. This is a more expensive air/fuel sensor. I've seen several directory entries showing the same sensor in both upstream and downstream applications, which is wrong. If your upstream sensor isn't twice the price of the downstream sensor, you probably have the wrong part. My trouble code is only for the bottom sensor. I replaced both the top and bottom sensors based on my internet research. The top sensor can fail (silently) enough to trigger the bottom sensor. Also, they're rated for 100,000 miles, and I was 120,000. You don't want to contaminate an expensive Prius catalytic converter, especially if you have a California car!