how many sensors are in 2002 Subaru Forester and how much to repair?

Check Engine Light Due to Failed Front O2 Sensor on Subaru Forester Problem Description and Possible Solution The front oxygen (air fuel ratio) sensor element may develop a crack, causing the Check Engine Light to illuminate. Subaru has recalled certain models to replace sensors that may fail. The Subaru service program number is WXW-80, this is not a government mandated recall. Problem Data RepairPal Verified Average mileage: 133,131 (35,000–389,000) 12 model years affected: 1998, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2009, 2011, 2012