Your first line of defense is to post this question to the TECH section. One of the highly skilled and knowledgable guys over there might have some idea for you to check on. My input to this is-gas brands will not have any effect lke the one you described. Bad gas might cause the problem, but you would notice that the engine is not running right. If he fuel is too low in octane, the knock sensors might cause the light to come on. Another, more simple problem could be the gas cap. make sure the gasket is ok and it is secure. You can try to replace th gas cap, but the best solution is to have the troule code read with a diagnostic tool. Hope this helps...
Gary

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