You’re running into a problem with starting your lawn mower. You can’t even get the engine to turn over. When this happens, begin with checking the battery and then move on to electrical and starter problems.
A lawn mower won’t turn over when the battery charge is low; the battery is bad; cables and wiring are loose; electrical components are corroded; the ignition switch or safety switch is faulty; the starter solenoid or starter is bad, or a fuse is blown.
Take caution when working with the electrical system to avoid electrocution. Follow all safety guidelines prior to working on a lawn mower. Have a professional mechanic troubleshoot and repair the mower when you are unsure of your skill level or how to perform repairs safely.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
This is Why Your Lawn Mower Won’t Turn Over
Dead or Bad Battery
Your lawn mower won’t have enough power to turn over when the battery is dead or has a low charge. Start with checking the battery’s charge with a voltmeter.
A fully charged 12-volt battery should give you a reading of about 12.7 volts. You must charge the battery if you are getting a reading lower than this.
For instructions on testing the battery, refer to the steps in “5 Things That Are Draining the Life of Your Lawn Mower Battery”. Here you will also find information on items that can cause your battery to lose charge including leaving the key on and a bad charging system.
It’s important to keep your battery charged, especially during storage, to extend your battery’s life. In cold weather, the battery can freeze and go bad when it isn’t fully charged.
Charge a Battery: Use a battery charger to charge your battery if needed. Before you continue, wear protective gear to protect your eyes and skin from electrical shock. Follow these steps to charge your lawn mower battery with a charger:
- Access the battery and terminals. You may need to use a screwdriver to uncover the battery. Do not remove the battery from the casing.
- Connect the charging cables beginning with the positive cable first. This is the red cable or the one with the plus sign. Place the cable on the positive battery terminal.
- Attach the negative cable to the negative battery terminal. This is the black cable or the one with the negative sign.
- Do not touch anything that doesn’t have a rubber coating to prevent electrocution.
- Set the charger’s voltage and amperage level to the desired level. The average volt level for lawn mower batteries is usually 12 volts. More amperage charges the battery faster. Start with two amps and work up to no more than 10 amps. A slow charge is best.
If the battery fails to hold a charge it must be replaced with a new battery. You can purchase a new battery at your local lawn mower dealership, hardware store, or automotive store.
Bring your old battery with you. Most places will charge you a core fee unless you provide them with your old battery.
Loose or Wires and Connections
It isn’t uncommon for the battery cables, wiring, and connections to come loose on the mower. A lawn mower shakes and vibrates while running which can cause a break in continuity when the electrical components are no longer securely in place.
In addition to loose wiring, moisture will cause connections and terminals to corrode contributing to a lack of good continuity.
Remove the corrosion using a baking soda solution (2 cups water to 3 heaping tablespoons of baking soda). Secure any loose wires and connections.
If you find wires, connections, or terminals are damaged or severely corroded, replace them with new components.
A fuse is installed to protect your lawn mower’s electrical system. Check your mower to make sure you don’t have a blown fuse.
If you’re unsure if the fuse is blown, you can check it by placing a multimeter probe on each prong of the fuse to measure resistance. A resistance reading near 0 means your fuse is good. An infinity resistance reading indicates a bad fuse.
Replace a blown fuse with a fuse with the same amperage as the fuse you are replacing. If you continue to blow fuses, you should bring your mower to your local lawn mower repair shop or dealership to find the root cause of the problem.
Bad Ignition Switch
When you insert the key into the ignition switch or flip the toggle switch for mowers with an on/off switch, your mower will fail to turn over and start when the switch is bad.
Check the switch using a multimeter to check continuity to determine if the ignition switch is the problem. To do this, look for the prongs marked “B” for Battery and “S” for Starter Solenoid.
Insert the key and turn it to the start position. With the multimeter set to measure resistance, touch one probe to the B prong and the other probe to the S prong.
A good ignition key switch will measure resistance near 0 ohms. A bad ignition key switch will measure infinite resistance and will need to be replaced.
Bad Safety Switch
Your lawn mower has an operator presence control system installed to keep you safe.
This is a system that includes safety switches to prevent a mower from starting if certain events are not met like engaging the brake on a ride-on mower or not holding the bail lever against the handle on a push mower.
A safety switch can be defective and cause a mower to fail to turn over. Test the switch using a multimeter. You can also temporarily bypass a safety switch to identify a bad switch, but only do this for troubleshooting purposes.
Never operate a mower without the safety switch. Never run a mower when a safety switch is bypassed. A safety switch can save you from serious injury and you never know when you’re going to need it.
Bad Starter Solenoid
A starter solenoid is an electromagnetic switch that, when engaged, initiates the starter motor to turn over the lawn mower engine.
The starter solenoid can go bad when the spring becomes weak or the copper plate begins to corrode. A weak starter, bad battery, or bad ground can also cause the solenoid to fail.
Before you test your starter solenoid, you must have a fully charged battery. Continue testing the solenoid by using the steps to diagnose a bad starter solenoid in “How to Tell Your Lawn Mower Solenoid is Bad”.
Bad Starter Motor
Once you have ruled out the battery, cables, wiring, ground, and starter solenoid as being the reason for a lawn mower not turning over, it’s time to look at the starter. The starter can be removed and tested.
I recommend having your local repair shop that specializes in starter and alternator repairs test your starter and rebuild it if possible before just throwing a pricey new starter at your lawn mower.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.
For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.