Check engine light

Get the CEL codes read, many auto parts stores read them for free. Late model Subarus tend to flash the cruise and VSC lights when CEL is on.

"tend"="always"

bring it too the local AUtozone store and they will check your engine light for you free of charge and should print out a paper telling the probable causes of the code . ( Please do not buy parts based on this print out it is just a staring point ) do a little more research before throwing parts at it

also a lot of times a code will come up for the O2 sensor but this doesn't mean the O2 sensor is bad it is just that it is detecting an out of spec condition The Light is supposed to come on ,some people think the O2 sensor is bad and replaced it ( pretty costly in some instances ) but it is really working like it is supposed to

False positive O2 codes were prevalent on 2004-2005 CA spec (PZEV) 2.5i, but with the variable valve tech and simplified emissions system used in 2006+ the great majority of scanned codes are not false.

ok so if a bad 02 sensor shows up as the code the o2 sensor may actually be at fault ???

Uhhh...yes. Maybe you need to restate the question?