Check engine light
Too numerous to list... Get the code read... Most part stores have a hand held OBD scanner that will read 'most' codes.
Yes, retrieve the codes then you have to see what conditions will cause the code to set to find the ROOT cause of the problem. You don't want to just start throwing parts at it.
Search Subaru Forester Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Subaru Forester Experts