O2 Oxygen Sensor Upstream for Subaru Honda (2001-2006)Optimizing Air Fuel Management for the EJ25 and D17 Platforms Who Its For: Engineered for owners of the Subaru EJ25 (SOHC) and Honda D17 series engines who are seeing a dip in fuel economy or a sluggish mid range response. Whether you are daily driving a Forester or maintaining a Civic EX, your engines ability to "breathe" efficiently depends entirely on the accuracy of its feedback loop. The Symptom: The factory sensors on the 2. 5L Boxer and 1. 7L