If your Sun Joe lawn mower will not start or stops while mowing, disconnect it from power and complete the checks below. Both covered models use the same safety-start system, overload protection, and extension-cord requirements.
Models Covered
| Model | Power type |
|---|---|
| MJ401E | 120V corded electric, 12 amp |
| MJ401E-PRO | 120V corded electric, 13 amp |
Safety first: Release the switch lever, unplug the mower, and wait for the blade to stop completely before inspecting the deck, blade, discharge channel, power cord, or extension cord. Wear protective gloves near the blade.
Troubleshooting Steps
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Check the power supply
Confirm that the extension cord is firmly connected to the mower and a working GFCI-protected outlet. Check the outlet, circuit breaker, or fuse. Do not use a damaged cord, plug, or outlet.
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Check the extension cord
Use an outdoor-rated extension cord no longer than 100 ft (30 m). The required wire gauge is:
- Up to 50 ft (15 m): 14 AWG
- More than 50 ft and up to 100 ft (15–30 m): 12 AWG
An undersized cord can cause low power, overheating, or an unexpected shutdown.
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Allow the motor to cool
Both models have thermal overload protection. If the mower stopped under a heavy load, unplug it and allow the motor to cool for a short period. Clear the cause of the overload before restarting.
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Check the overload reset button
Locate the rectangular overload-circuit reset button beside the safety lock button on the handle controls. After the motor has cooled and the overload has been cleared, press the reset button once.
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Clear the cutting area
With the mower unplugged and the blade fully stopped, check that the blade can rotate freely and remove packed grass or debris from the discharge channel and housing. Never place your hands under the mower while it is connected to power.
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Use the correct starting sequence
Place the mower on short grass or a previously mowed area. Press and hold the safety lock button, then pull the switch lever toward the handle. Once the motor starts, release the safety lock button while continuing to hold the switch lever.
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Reduce the cutting load
If the mower starts but loses power or stops again, raise the cutting height and make narrower passes. Clean blocked air vents and avoid forcing the mower through tall, thick, or wet grass.
Stop using the mower immediately if the cord is cut or damaged, the reset or circuit breaker trips repeatedly, or you notice smoke, a burning smell, unusual noise, severe vibration, or blade damage. Disconnect the mower and do not restart it.
Still Not Working?
Contact Shop Joe Customer Support at 1-866-225-9723. Have the model number, serial number, proof of purchase, and a description of what happened before the mower stopped available. Do not disassemble the motor, switch housing, or electrical components.