While this might not be your issue it should guide you on what to look for: [https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/16671-solved-820-3115-runs-slow-th1h-fin-stack-sensor-failing|13” MacBook Pro - 820-3115 runs slow (Th1h Fin Stack sensor failing)]
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While this might not be your issue it should guide you on what to look for: [link|https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/16671-solved-820-3115-runs-slow-th1h-fin-stack-sensor-failing|13” MacBook Pro - 820-3115 runs slow (Th1h Fin Stack sensor failing)]
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The I/O board has the sensor on it near the heat sink heat transfer fin.
While this might not be your issue it should guide you on what to look for: [https://www.rossmanngroup.com/boards/forum/board-repair-troubleshooting/16671-solved-820-3115-runs-slow-th1h-fin-stack-sensor-failing|13” MacBook Pro - 820-3115 runs slow (Th1h Fin Stack sensor failing)]