Denso part number 234-9123 is a replacement air/fuel ratio sensor for 2006 Saab 9-2X, 2006-2010 Subaru Forester, 2006-2011 Subaru Impreza, 2006-2009 Subaru Legacy, and 2006-2009 Subaru Outback vehicles. Denso Air/Fuel Ratio Sensors are manufactured and tested to the strictest OE standards for unparalleled performance. Each component is precision-built for exact replacement, and a first time fit. The superior design of Denso Air/Fuel Ratio Sensors maximizes engine performance and fuel efficiency while reducing fuel consumption and harmful emissions. Denso Air/Fuel Ratio Sensors increase performance by mapping air/fuel ratios throughout the RPM range. They also reduce emissions by keeping the air-fuel mixture at an optimum ratio. Optimal air/fuel ratios reduce fuel consumption and maximize catalytic converter life. Denso gives you the right part and the right fit, the first time. .