When your lawn mower refuses to start, the starter is often the first component blamed. Learning how to check lawn mower starter yourself can save you time and money before you call for repairs. Before you assume the worst, a few simple checks can determine if your lawn mower starter is the problem. This guide will walk you through a logical, step-by-step diagnostic process that is safe and effective for most walk-behind and riding mowers.
How To Check Lawn Mower Starter
A systematic approach is key to accurate diagnosis. The starter motor itself is just one part of a larger starting system. Jumping straight to replacing it might not fix the issue if another component has failed. Follow these steps in order to isolate the true cause of your starting troubles.
Preliminary Safety Checks And Preparations
Always prioritize safety before working on any machinery. A simple mistake can lead to injury or further damage to your mower.
- Disconnect the Spark Plug: This is the most critical step. Locate the spark plug wire and pull it firmly off the plug’s terminal. This prevents the engine from accidentally starting while you are working.
- Engage the Parking Brake: For riding mowers, always set the brake.
- Ensure the Mower is on Level Ground: This provides stability and prevents rolling.
- Gather Basic Tools: You will likely need a wrench or socket set, a screwdriver, a multimeter for electrical testing, and possibly a pair of jumper cables or a known-good battery.
Step 1: Verify The Obvious – Fuel, Switch, And Blade Engagement
It sounds simple, but many “starter problems” are actually operator errors or basic oversights. Eliminate these possibilities first.
- Check the Fuel Level: Is there fresh, clean gasoline in the tank? Old fuel can cause starting issues that mimic a bad starter.
- Inspect the On/Off Switch and Key: Ensure the switch is in the “on” position. For riding mowers, make sure the key is turning fully.
- Disengage the PTO/Blades: On many riding mowers and some walk-behinds, the engine will not crank if the cutting blades are engaged. Make sure the PTO lever or switch is off.
- Check the Seat Safety Switch (Riding Mowers): Most riders have a switch under the seat that must be depressed. Sit firmly in the seat or check if the switch is stuck or damaged.
Step 2: Listen For The Click – Diagnosing The Solenoid
When you turn the key or push the starter button, listen carefully. The sounds your mower makes are excellent diagnostic clues.
- The Healthy Crank: A rapid, whirring sound means the starter motor is spinning the engine properly. If the engine doesn’t fire, your problem is likely fuel, spark, or compression, not the starter.
- The Single Loud Click: This usually indicates the starter solenoid is engaging, but power is not reaching the starter motor. The solenoid is a heavy-duty relay that connects the battery to the starter. A click means it’s trying, but it or its connections may be faulty.
- Rapid Clicking: This typically points to a weak or dead battery. The solenoid is trying to engage repeatedly but lacks sufficient voltage to hold.
- Complete Silence: If you hear absolutely nothing, the issue is likely in the safety switches, ignition switch, wiring, or a completely dead battery connection.
How To Test The Solenoid Directly
If you suspect the solenoid, you can perform a bypass test. Locate the solenoid (usually a small cylinder near the battery or starter). It will have two large terminals and one or two small wires. Use an insulated screwdriver to carefully bridge the two large terminals. If the starter immediately engages and spins, the solenoid is faulty. If nothing happens, the problem is likely the starter motor or its direct connection.
Step 3: Test The Battery And Electrical Connections
A weak battery is the single most common cause of starting failure. Even if the lights seem bright, a starter motor requires a massive amount of current.
- Visual Inspection: Check the battery terminals for thick, white or blue corrosion. Clean them with a wire brush and a solution of baking soda and water.
- Check Cable Tightness: Ensure both the positive (red) and negative (black) battery cables are tight on the terminals and at their other connection points, especially where the negative cable attaches to the mower’s frame or engine block.
- Test Battery Voltage: Use a multimeter set to DC volts. A fully charged 12-volt battery should read about 12.6 volts. Anything below 12.0 volts is likely insufficient. Have the battery load-tested at an auto parts store for a definitive answer.
- Perform a Voltage Drop Test: With the help of a friend trying to start the mower, place the multimeter probes on the battery’s positive terminal and the starter’s main power terminal. A reading over 0.5 volts indicates high resistance in the cable or connections, starving the starter.
Step 4: Inspect The Starter Motor Directly
If power is reaching the starter but it doesn’t spin, the motor itself may be faulty. Before removal, check the single small wire (the “S” terminal) on the solenoid that triggers it. Ensure it is connected and not damaged.
Bench Testing The Starter Motor
To conclusively test the starter, you often need to remove it. Once off, you can perform a simple bench test.
- Disconnect the battery.
- Remove the starter mounting bolts and disconnect the wires, noting their positions.
- Place the starter on a non-conductive surface. Connect a jumper cable from the negative (-) battery post to the starter’s metal case.
- Momentarily touch another jumper cable from the positive (+) battery post to the starter’s main power terminal (where the thick cable was). Caution: The starter may jump or spin violently. If it spins strongly, the starter motor is likely good. If it does nothing, spins weakly, or makes grinding noises, it is faulty.
Step 5: Examine The Starter Bendix And Flywheel
The starter motor drives the engine via a small gear called a Bendix or pinion gear. This gear should extend to mesh with the large ring gear on the engine’s flywheel when activated.
- Visual Inspection: Look at the starter gear and the flywheel teeth you can see through the starter opening. Look for missing, chipped, or worn-down teeth.
- Stuck Gear: Sometimes the Bendix gear gets stuck in the extended position, preventing it from engaging properly. Tapping it gently with a rubber mallet might free it, but this is often a sign of internal wear.
- Flywheel Issues: If the flywheel teeth are damaged, the starter gear cannot engage, resulting in a loud grinding noise. This requires engine disassembly to replace the flywheel, which is a more significant repair.
When To Repair Vs. Replace Your Starter
Starter motors can sometimes be rebuilt. Common serviceable parts include the brushes (small carbon blocks that conduct electricity) and the solenoid. However, for most homeowners, replacement is more cost-effective and reliable than a rebuild.
- Consider Repair If: You have a vintage or expensive commercial mower, and you are comfortable with detailed disassembly. Replacement brush kits are inexpensive.
- Consider Replacement If: The starter housing is damaged, the armature is burnt out, or the Bendix drive mechanism is broken. New or remanufactured starters offer a warranty and are a straightforward swap.
Preventative Maintenance For Your Starting System
Regular care can prevent most starter issues from occuring in the first place.
- Keep Battery Terminals Clean: Check and clean them at least once a season.
- Use a Battery Tender: If you store your mower for the winter, a maintainer keeps the battery at full charge and prevents sulfation.
- Address Engine Problems Promptly: A hard-to-start engine due to carburetor or spark issues puts extra strain on the starter and battery.
- Listen for Unusual Noises: A slight grinding sound when starting is a early warning sign of flywheel or Bendix gear wear.
Frequently Asked Questions
What are the symptoms of a bad lawn mower starter?
The main symptoms include a single loud click with no engine crank, complete silence when turning the key, a grinding noise during cranking, or the starter spinning freely without engaging the engine. Intermittent starting, where it works sometimes and not others, is also a common sign.
Can you jump-start a lawn mower with a bad starter?
No, you cannot. Jump-starting only addresses a weak battery. If the starter motor itself is mechanically or electrically failed, providing more power from another battery will not make it work. The starter must be repaired or replaced.
How do I know if its the starter or the solenoid?
Listen for the click. A single, solid click usually points to the solenoid or its connections. You can test by bypassing the solenoid with a screwdriver (as described above). If the starter spins when bypassed, the solenoid is bad. If there’s no click at all, the problem could be earlier in the circuit (switches, wiring) or a completely dead battery.
Why does my starter just make a clicking sound?
A rapid clicking sound is almost always a sign of a weak or discharged battery. The battery has enough voltage to pull in the solenoid relay, but not enough to power the starter motor, causing the solenoid to click on and off repeatedly. A single, loud click suggests a faulty solenoid or a bad connection at the starter.
Is checking a lawn mower starter difficult?
Not really. The process is mostly about logical elimination and requires basic tools. Most of the checks—like listening for sounds, inspecting the battery, and cleaning connections—are simple and require no mechanical expertise. The bench test is the most advanced step, but it follows a straight-forward procedure.
By following this structured guide, you can confidently diagnose your lawn mower’s no-start condition. Remember to always work safely, start with the simplest explanations, and work your way toward the more complex ones. With a bit of patience, you’ll identify whether the issue is a simple loose wire, a dead battery, or a faulty starter that needs replacement.