Review on Denso 234-9123 Oxygen Sensor: Reliable Air and Fuel Ratio Monitoring Device by Kevin Ayala

Direct replacement for 2006 Impreza (and many other models and years). The first let air through the stem right out of the box. Revain accepted the return with no problems. A Few Installation Tips: Getting the old one out is the hardest part. There they are often strongly baked. Removing the headers isn't too difficult. If the misaligned O2 sensor socket does not come off easily, simply pull on the headers. If the old one comes out easily, this one should go in easily. If the old one took a lot of convincing it would be wise to get a tap and clean the internal threads before attempting to screw this in. Lightly pressurize the system and spray all fittings (oxygen sensors, manifolds) with soapy water. Bubbles = Leaks.