O2 Oxygen Sensor 1 Upstream Rear For Mitsubishi Endeavor Lancer (2004-2011)Restore your Mitsubishis fuel economy and eliminate that stubborn Check Engine Light with a sensor designed to survive the high heat cycles of the 4G94 and 6G75 platforms. Replacement Upstream or Downstream Oxygen Sensor for Mitsubishi Lancer, Montero, and Endeavor If you've noticed a sudden drop in MPGs or a sluggish throttle response in your Lancer or Montero, your factory O2 sensors are likely "lazy" or completely fouled. On these Mitsubishi