Subaru Repair: Check engine light, subaru forester, goodyear auto

Question
QUESTION: I have a 2002 Subaru Forester.  The check engine light came on and I had it diagnosed. (I checked the gas cap first and it was on tight and the tank had been filled about a week before light came on.)   I was told it was the knock sensor causing the light.   The sensor and sensor circuit checked out Ok.  The engine checked out Ok also.  It was suggested I use a higher octane gasoline.  Have now filled up twice with 89 octane gas and also put in an additive.  The light still periodically comes on and stays on for a day or less and then goes out and stays out for a couple days.  Any suggestions?
ANSWER: Who tested the knock they almost always fail in that ara car

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QUESTION: The problem was diagnosed by a Goodyear auto service garage.

Answer
Thats the first problem.Most shops have a generic scan tool.The sample rate on a Subaru specific diagnostic tool is much faster.A tire and repair shop such as good year would go broke buying each manufactures specific scan tool.
Best Suggestion i have is to take it to someone Who Knows Subaru.