If the mower is shutting down during use, this is most likely being caused by mower overload.

Your self drive has built-in overload circuit protection. If your mower self drive shuts off, release the bail handle, wait at least 10 seconds and try again. If you are cutting tall grass, slow the self drive to the lowest speed position. To prevent damage due to overload conditions, do not try to remove too much grass at one time. Slow down your cutting pace or raise the cut height.