engine light was on now my car wont shift into passing gear could it be tcm?

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i went to O Reillys n they said it was mass air flow ,that did't work then i went to auto zone n they said it had an 0715 reading. my engine light did not go off. I took it to mechanic and he drove it n said the engine light went off w/o him doing anything.Next day I drove it to work n light was off as I started to leave work light come back on