smog detector on 2001 Subaru Forester

85,000 miles
check engine light comes on, goes off after several days, comes on again
mechanic said it was a smog detector?
please locate this for me and offer insight into replacement

1 answer
There is no "smog detector". Here is background on the check engine light that will get you started on the right path to getting the problem fixed: http://repairpal.com/check-engine-light