Diagnosis
The tool operates briefly then cuts power. This is thermal overload protection. The motor or motor controller is overheating due to excessive load or a fault.
How to Fix It
Checklist. 1: Verify you are using a high-output M18 REDLITHIUM battery (XC or HD series recommended). 2: Clear all wrapped debris from the trimmer head and shaft coupler. 3: Allow the tool to cool down completely in a shaded area for 30 minutes. 4: Attempt to use it with a light load (no line advanced, just spinning free). If it still shuts off, proceed.
If That Didn't Work
The problem is likely a failing motor or a faulty thermal sensor. Test with a different, known-good high-output M18 battery. If the issue persists with a different battery, the tool requires service.
Heads Up
Do not attempt to bypass thermal protection. The Power State™ brushless motor management system is integral. Repeated triggering after shutoff can cause permanent damage to the electronic components.