Engine light has come on .What problems could occur because of this

Hello, I do not suspect the fuel change to be much related, although if the Matrix requires premium fuel and you are not using premium fuel, the engine's processor is likely trying to retard the timing to compensate for the fuel change. I honestly am not sure if that vehicle requires premium, though. In any case, a myriad of causes exist for check engine lights coming on. Have a diagnostic test performed, or if you want to, obtain a code reading tool from a parts store to learn what codes are stored causing the light to come on. You can research further from there. Good luck!