When your lawn mower refuses to start, a faulty solenoid is a common culprit. Learning how to test a solenoid on a lawn mower can save you time and money, getting your equipment running again quickly. A faulty solenoid can prevent starting, but testing it with a multimeter is straightforward. This guide will walk you through the entire process, from locating the part to interpreting your multimeter readings.
You do not need to be a professional mechanic. With basic safety precautions and a simple digital multimeter, you can diagnose the problem in minutes. We’ll cover everything you need to know.
How To Test A Solenoid On A Lawn Mower
This section provides the core step-by-step procedure. Before you begin, ensure your mower is on a flat, stable surface and the ignition key is removed. Disconnect the spark plug wire for added safety.
Tools And Materials You Will Need
Gathering the right tools before you start makes the job smoother. You likely have most of these already.
- A digital multimeter (set to measure Ohms for resistance and Volts for continuity).
- A set of basic wrenches or socket drivers.
- Safety glasses and work gloves.
- A wire brush for cleaning connections.
- A piece of sandpaper or emery cloth.
Locating The Lawn Mower Solenoid
The solenoid is usually a small, cylindrical component with two or three large terminals and one or two small wire terminals. It is typically mounted on the mower’s frame near the battery or the starter motor. Follow the positive (red) cable from the battery; it will lead directly to one of the solenoid’s large terminals.
Common Solenoid Appearances
- Three-Terminal Solenoid: Has two large terminals and one small terminal. The second large terminal connects to the starter motor.
- Four-Terminal Solenoid: Has two large terminals and two small terminals. The extra small terminal is often for a ground wire or an ignition switch connection.
Step-By-Step Testing Procedure
Follow these steps in order to safely and accurately test your lawn mower’s starter solenoid.
Step 1: Perform A Preliminary Click Test
This quick check can give you an initial clue. Sit in the operator’s seat, set the parking brake, and ensure all safety switches are engaged. Turn the ignition key to the “start” position. Listen carefully for a solid, audible clicking sound coming from the solenoid’s location.
- A loud, singular click often indicates the solenoid is engaging but there may be another issue (like a bad starter or dead battery).
- A rapid series of clicks usually points to a weak or undercharged battery.
- Complete silence strongly suggests a problem with the solenoid, safety switches, ignition switch, or wiring.
Step 2: Check Battery Voltage First
Always rule out the battery before condemning the solenoid. Use your multimeter set to DC Volts (20V range). Place the red probe on the battery’s positive terminal and the black probe on the negative terminal. A healthy, fully charged battery should read at least 12.6 volts. If it reads below 12.4 volts, charge it fully before proceeding.
Step 3: Clean The Solenoid Terminals
Corrosion on the terminals can block current flow, mimicking a solenoid failure. Disconnect the battery cables (negative first, then positive). Use a wire brush and sandpaper to clean all solenoid terminals and battery cable ends until they are shiny and bright. Reconnect the battery (positive first, then negative) and try the click test again.
Step 4: Test For Power At The Solenoid
With the multimeter still set to DC Volts, check for power arriving at the solenoid. Connect the black probe to a clean, unpainted metal part of the mower frame (a good ground). Touch the red probe to the large terminal where the battery cable connects. You should see a reading very close to your battery’s voltage (e.g., 12.6V). If not, there’s a wiring issue between the battery and solenoid.
Step 5: Test The Solenoid’s Internal Switch (Continuity Test)
This is the definitive test for the solenoid’s main function. Disconnect all wires from the solenoid for safety. Set your multimeter to the Ohms (Ω) setting for resistance.
- Place one probe on each of the two large terminals.
- The meter should show “OL” (Open Loop) or infinite resistance, meaning no connection exists internally.
- Now, take a short, insulated jumper wire and momentarily connect it from the large battery terminal to the small “S” (start) terminal on the solenoid. You should hear a distinct click.
- With the jumper wire still connected, check the resistance across the two large terminals again. The reading should now drop to near zero Ohms (0.1 – 0.5 Ω), indicating the internal switch has closed.
If the solenoid clicks but the resistance remains infinite, the internal contacts are burned out and the solenoid is faulty. If it does not click at all when you apply the jumper wire, the solenoid’s coil is likely dead.
Step 6: Test The Small Control Terminal
This tests the signal from the ignition switch. Reconnect the battery and the small wire to the solenoid’s “S” terminal. Set your multimeter back to DC Volts. Place the black probe on ground and the red probe on the small terminal. Have an assistant turn the ignition key to “start.” You should see a voltage reading (usually 12V) appear on the meter while the key is held. If you get no voltage here, the problem is upstream in the ignition switch, safety interlock system, or related wiring.
Interpreting Your Test Results
Your multimeter readings will point you to the specific issue.
- Solenoid Clicks, Passes Continuity Test: The solenoid is functioning. Look at the starter motor or engine mechanical issues next.
- Solenoid Clicks, Fails Continuity Test: The solenoid is bad. The internal contacts are arced and burned, preventing current flow to the starter.
- Solenoid Does Not Click, No Voltage at Small Terminal: The solenoid may be fine. Diagnose the ignition switch, safety switches (like the seat or blade engage switch), and related wiring.
- Solenoid Does Not Click, Has Voltage at Small Terminal: The solenoid’s internal coil is defective. The solenoid needs to be replaced.
How To Replace A Faulty Solenoid
If your tests confirm a bad solenoid, replacement is simple. Always purchase the correct part for your specific mower make and model.
- Disconnect the negative battery cable first, then the positive.
- Take a picture of the solenoid wiring or note which wire goes to each terminal.
- Using the appropriate wrench, remove the nuts securing the wires to the solenoid terminals.
- Unbolt the solenoid from its mounting bracket.
- Position the new solenoid and bolt it in place.
- Reattach all wires to their correct terminals, matching your photo or notes. Tighten the nuts securely.
- Reconnect the battery positive cable, then the negative cable.
- Test the starting system. The mower should crank normally if the solenoid was the only issue.
Essential Safety Tips And Precautions
Working on electrical systems requires caution. Ignoring safety can lead to injury or further damage to your equipment.
- Always disconnect the spark plug wire and battery before beginning any work.
- Never bypass the solenoid by directly connecting the battery to the starter with a jumper cable; this can cause a dangerous short circuit or fire.
- Wear eye protection when cleaning terminals or making connections.
- Ensure the mower is on level ground and the parking brake is set.
- Double-check all connections are tight and clean after reassembly. A loose connection can create high resistance and heat.
Frequently Asked Questions
What Are The Symptoms Of A Bad Solenoid On A Lawn Mower?
The most common symptom is a complete lack of response when you turn the key—just silence. Sometimes you may here a single loud click but no engine cranking. In rare cases, the starter may engage sporadically or only after multiple key turns.
Can You Bypass A Lawn Mower Solenoid To Start The Mower?
Technically, yes, but it is not recommended as a fix, only as a brief diagnostic test. You can use a heavy-duty screwdriver with an insulated handle to carefully bridge the two large solenoid terminals momentarily. If the starter engages, it confirms the solenoid is bad. This should be done with extreme caution, as it can spark and bypass all safety systems.
Why Does My Solenoid Click But The Starter Not Engage?
A clicking solenoid that passes power to the starter indicates the solenoid itself is working. The problem then lies with the starter motor, a weak battery that cannot supply enough current, or poor connections at the battery or starter cables. Corroded connections are a very frequent cause of this issue.
How Much Does It Cost To Replace A Lawn Mower Solenoid?
A replacement solenoid typically costs between $15 and $50, depending on your mower model. They are generally inexpensive parts. Labor costs if hired out could add another $50 to $100, but the job is very DIY-friendly and often takes less than 30 minutes.
Is A No-Click Situation Always The Solenoid’s Fault?
No, not always. A lack of clicking often points to the control circuit. This includes a discharged battery, a faulty ignition switch, a disengaged safety switch (like under the seat or on the brake pedal), or broken wiring. This is why testing voltage at the small solenoid terminal is a crucial diagnostic step.