If your Sun Joe cordless lawn mower will not start, the cause may be a missing safety key, an incorrect start-up sequence, a discharged or faulty battery, grass or debris blocking the deck, or grass that is too tall for the current cutting-height setting.
Complete the checks below in order. Refer to your mower’s operator’s manual whenever its controls or battery setup differ from this general guide.
Before Inspecting the Mower
Release the motor/blade control, remove the safety key, remove all batteries, and wait for the blade to stop completely. Never place your hands under the mower deck or near the blade while a battery or safety key is installed.
Before Troubleshooting
Make note of the following:
- Mower model number
- Battery model and capacity
- Number of batteries required by the mower
- Battery charge-level lights
- Whether the mower makes any sound or movement when starting
- Whether the mower stopped during use or would not start from the beginning
Step-by-Step Start-Up Checks
- Move the mower to a safe location. Place it on a firm, level surface away from tall grass, loose objects, people, and pets.
- Check the safety key. Make sure the correct safety key is inserted fully in the position shown in the mower’s operator’s manual.
- Check every required battery. Press each battery’s charge-status button. Recharge any low or empty battery using the compatible charger.
- Reinstall the batteries. With the mower off, slide each compatible battery fully into its compartment until it clicks or locks securely. Close the battery-compartment cover.
- Use the correct start-up sequence. Engage the safety or start button and motor/blade control in the exact order shown in your mower’s manual. The control must remain engaged for the motor to run.
- Test the mower on short grass or a clear surface. If it starts away from tall grass, raise the cutting height before returning to the lawn.
Control reminder: Many cordless mowers require the safety/start button and bail lever or motor/blade control to be operated in a specific sequence. Do not tape, tie, bypass, or modify any safety control.
Check the Mower Deck
- Shut the mower down completely. Release the motor/blade control, remove the safety key and all batteries, and wait for the blade to stop.
- Wear protective gloves. Keep your hands away from the blade’s cutting edges.
- Inspect the discharge opening and deck. Look for packed grass, clippings, sticks, or other debris that may prevent the blade from turning freely.
- Remove loose debris with a nonmetal tool. Never use bare hands, water, or a hose to clean the underside of the mower.
- Return the mower upright. Reinstall the batteries and safety key only after the mower is correctly positioned and the work area is clear.
Blade Safety
Blade movement can cause serious injury. Do not rotate, straighten, sharpen, or remove the blade as part of general start-up troubleshooting. If the blade is bent, damaged, jammed, or difficult to turn after loose debris is cleared, contact Shop Joe Support or a qualified service provider.
Quick Cause and Solution Guide
| Possible Cause | What to Check | Recommended Action |
|---|---|---|
| Safety key is missing or not fully inserted | Confirm the correct key is seated in its operating position. | Insert the safety key as shown in the mower’s manual. |
| Motor/blade control is disengaged | Review the required safety-button and control-lever sequence. | Repeat the model-specific start-up sequence. Keep the motor/blade control engaged while operating. |
| Battery is discharged | Press the status button on every required battery. | Fully charge low batteries with the compatible charger before retesting. |
| Battery is not fully installed | Check that every required battery is in the correct compartment and locked in place. | Remove and reinstall each battery until it clicks securely. |
| Battery may be faulty | Look for no status lights after charging, physical damage, swelling, leaking, or unusual heat. | Stop using a damaged or unresponsive battery and contact Shop Joe Support. Do not open or repair it. |
| Mower deck is clogged | With the key and batteries removed, inspect for packed grass or debris. | Clear only loose debris using gloves and a nonmetal tool. |
| Grass is too tall | Test the mower away from tall or wet grass. | Raise the cutting height and mow slowly. Remove only a portion of the grass height per pass. |
Troubleshooting Results
The mower starts after the battery is charged or reinstalled
What this means
The battery was discharged or was not fully connected. Charge batteries before use and make sure every required pack locks into place.
The mower starts only away from tall grass
What this means
The blade may be overloaded at the current cutting height. Raise the deck, begin on shorter grass, and reduce the amount cut in each pass.
The mower clicks, hums, or attempts to start
What to do
Release the control immediately. Remove the safety key and all batteries, then inspect the deck for loose obstructions. Do not repeatedly attempt to start a jammed mower.
The mower remains completely unresponsive
What to do
Confirm the safety key, battery charge, battery installation, and model-specific start sequence once more. If the mower remains unresponsive with charged compatible batteries, contact Shop Joe Support.
Do Not Attempt Internal Repairs
Do not open, bypass, modify, or repair the mower’s wiring, switches, motor, battery, charger, safety key, or electronic controls. Stop using the mower if you notice smoke, sparks, a burning odor, melted parts, damaged wiring, battery swelling, or unusual heat.