Recently, my completely stock '02 WRX wagon threw a CEL (P0031 code) at 50,500 miles. I cleared the ECU (disconnected battery for a few hours) then (took a shot) replaced the front A/F sensor with a Bosch universal sensor. After installation, the CEL is still up. Frustrated and out of patience, I took the car to a local (non-dealer) Subaru mechanic. After a day of testing all relevant circuits, I was told that the ECU needs to be replaced.
I've heard some stories about blown A/F sensors damaging the ECU, how probable is it? In addition, is it possible that my universal A/F sensor damaged the ECU? This little CEL will cost me $1500 when all is said and done.