When your lawn mower refuses to start, the problem often lies with the starter motor. Learning how to test lawn mower starter is a crucial skill that can save you time and money. If your mower doesn’t crank, you can test the starter motor with a simple multimeter check. This guide will walk you through the entire process, from safety to specific tests, so you can diagnose the issue with confidence.
How To Test Lawn Mower Starter
Before you begin any testing, safety is the most important step. You will be working with electrical components and potentially flammable fuel. Always disconnect the spark plug wire to prevent any accidental engine starts. Make sure the mower is on a flat, stable surface and the engine is completely cool. Gather your tools: a multimeter, a set of wrenches or sockets, and some basic safety glasses and gloves.
Understanding The Starter Motor System
A lawn mower starter is part of a larger system. It’s not just the motor itself. The system includes the battery, which provides power; the solenoid, which acts as a heavy-duty switch; and the starter motor, which turns the engine over. Wiring and connections link all these parts together. A failure in any one of these components can prevent the starter from working properly. Your testing will need to check each link in this chain.
Common Symptoms Of A Bad Starter
- A single loud “click” when you turn the key, but no engine cranking.
- A repeated, rapid clicking sound from the engine area.
- The starter motor spins freely but does not engage the engine flywheel (a whirring sound).
- Complete silence when you turn the ignition key.
- Visible smoke or a burning smell coming from the starter motor.
Step-By-Step Testing Procedure
Follow these steps in order to systematically find the fault. Start with the simplest checks before moving to more complex tests.
Step 1: Perform A Visual Inspection
First, look for obvious problems. Check the battery terminals for heavy corrosion or loose connections. Inspect the wiring leading to the starter solenoid and motor for any signs of damage, fraying, or disconnection. Look at the starter motor itself for cracks or oil saturation. Sometimes, the issue is a simple loose wire that a visual check can reveal.
Step 2: Test The Battery Voltage
A weak battery is the most common cause of starting problems. Use your multimeter set to DC Volts (20V range). Place the red probe on the positive (+) battery terminal and the black probe on the negative (-) terminal. A fully charged 12-volt battery should read at least 12.6 volts. If it reads below 12.4 volts, charge the battery fully and retest. A battery that cannot hold a charge needs to be replaced.
Step 3: Check For Voltage At The Solenoid
The solenoid has two large terminals and one or two small terminals. One large terminal connects directly to the battery’s positive cable. With the multimeter still on DC Volts, place the black probe on the battery’s negative terminal or a clean engine ground. Touch the red probe to the battery-side large terminal on the solenoid. You should see full battery voltage (e.g., 12.6V). If not, there’s a break in the cable from the battery.
Next, have an assistant turn the ignition key to the “start” position. Test the other large terminal on the solenoid (the one that goes to the starter). It should now also show full battery voltage. If you get voltage here but the starter doesn’t run, the problem is likely the starter motor itself or its ground.
Step 4: Test The Starter Motor Directly
This is a bench test that checks the motor in isolation. You must first remove the starter from the mower. Consult your mower’s manual for specific removal steps. Once removed, you need to perform a simple direct power test.
- Set your multimeter to the Ohms (Ω) setting to first check for a ground. Place one probe on the starter’s metal case and the other on the starter’s power terminal. There should be no continuity (infinite resistance). If there is continuity, the motor is shorted internally and is faulty.
- For the power test, you will bypass all mower wiring. Use a set of jumper cables. Connect the black jumper cable from the negative (-) post of a known-good 12V battery to the metal body of the starter motor.
- Briefly touch the red jumper cable from the battery’s positive (+) post to the starter’s power terminal. Caution: The starter may jump and spin violently. Secure it in a vise or on the ground with your foot. If the starter motor spins strongly and smoothly, it is likely functional. If it does nothing, spins weakly, or makes grinding noises, it has failed.
Diagnosing Other Related Issues
Sometimes the starter motor tests fine, but other problems prevent it from working. Here are two common culprits.
Testing The Starter Solenoid
The solenoid can fail even if it clicks. Use your multimeter to check for continuity across its large terminals when activated. Set the multimeter to the Ohms or continuity setting (the one that beeps). With the ignition off, there should be no continuity. When an assistant turns the key to “start,” you should get continuity (a beep or near-zero resistance) as the solenoid’s internal contacts close. No continuity means a bad solenoid.
Checking The Starter Engagement
If the starter spins but doesn’t turn the engine, the problem is mechanical. The starter drive gear (called a Bendix) may be worn or stuck. When you remove the starter, inspect this small gear. It should move freely along its shaft and not be missing any teeth. It should only spin in one direction when turned by hand. If it’s stuck or spins freely in both directions, the starter drive assembly needs to be replaced.
What To Do After Testing
Your tests will point you toward a solution. If the starter motor failed the direct power test, you need to replace it. You can sometimes find rebuild kits, but for most homeowners, a new or remanufactured starter is the best option. If the solenoid failed, it’s a relatively easy and inexpensive part to swap out. Always reconnect the battery cables properly: positive first, then negative, and ensure all connections are tight and clean.
FAQ Section
How Do I Know If My Lawn Mower Starter Is Bad?
Signs include a loud single click without cranking, a whirring sound where the starter spins but doesn’t engage, or complete silence. Testing with a multimeter or a direct jump from a battery will confirm if the starter motor itself has failed.
Can You Test A Starter With A Screwdriver?
Yes, but this method bypasses the solenoid and can be dangerous. You can carefully bridge the two large terminals on the solenoid with an insulated screwdriver. If the starter cranks, the starter is good but the solenoid or ignition switch is likely bad. Wear gloves and eye protection, and ensure the mower is in neutral with the spark plug disconnected.
What Would Cause A Starter To Not Engage?
A starter that spins but doesn’t engage is usually caused by a faulty starter drive (Bendix gear). The gear may be stripped, stuck in the retracted position, or the mechanism that throws it forward is broken. This requires starter removal and inspection.
How Many Volts Does A Lawn Mower Starter Need?
Most riding lawn mower starters operate on 12 volts, the same as a car. Some smaller push mowers may have starters that run on lower voltages, but 12V is the standard. Always check your mower’s manual to be certian.
By following this structured approach, you can reliably diagnose your lawn mower’s starting problem. Start with the simple battery check, move to the solenoid, and finally test the starter motor directly. This process eliminates guesswork and helps you fix your mower quickly, getting your lawn back on track for regular maintenance.