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Verify the fluid temp sensor is reading correct and below 240 degrees while driving. If that is good then replace the fluid once again and reset the TCM. If it still occurs then its the TCM needing to be replaced.
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I have only had this code once, but there were other issues that required an overhaul to address, and no specific tasks were done to resolve this code alone. GM says service the fluid and reset the life counter. Nothing more nothing less, and nothing beyond that. I checked on what other techs did for this concern, and outlined that in my response.