How Does a Solenoid Work on a Lawn Mower?

Imagine you’re about to mow your lawn, but the engine just won’t start. You check the gas, the spark plug, and everything seems in order. Then, you notice a small, cylindrical component connected to your battery – the solenoid. It may not be the most glamorous part of your lawn mower, but this unassuming piece plays a crucial role in getting your engine roaring to life. This article delves into the fascinating world of solenoids, explaining how they work on lawn mowers and why they are essential for a smooth mowing experience.

In essence, a solenoid is an electrically controlled switch that allows a large current to flow through a circuit. It works by using an electromagnet to move a plunger, which in turn completes the electrical circuit. In the context of a lawn mower, this circuit powers the starter motor, enabling the engine to turn over and ignite.

The Anatomy of a Lawn Mower Solenoid

To fully understand how a solenoid functions, it’s helpful to break down its components:

1. Electromagnet:

This is the heart of the solenoid. It consists of a coil of wire wrapped around a metal core. When electricity flows through the coil, it creates a magnetic field that attracts the plunger.

2. Plunger:

The plunger is a metal rod that is attached to the core of the electromagnet. When the electromagnet is energized, the plunger is pulled towards the core, completing the circuit.

3. Contact Points:

These are the points where the electrical current flows through the circuit. The plunger acts as a switch, connecting the contact points when it is pulled towards the core.

4. Housing:

The solenoid is enclosed in a protective housing that shields it from the elements and keeps it securely mounted to the lawn mower’s frame.

How the Solenoid Starts Your Lawn Mower Engine

Now let’s break down the process of starting your lawn mower engine with the help of the solenoid:

  1. Turning the Key: When you turn the key to the “start” position, a small amount of electricity flows from the battery to the solenoid.
  2. Electromagnet Activation: This current energizes the electromagnet, generating a magnetic field.
  3. Plunger Engagement: The magnetic field attracts the plunger, pulling it towards the core.
  4. Circuit Completion: As the plunger moves, it makes contact with the contact points, completing the circuit.
  5. Starter Motor Power: This completed circuit allows a large current to flow from the battery to the starter motor.
  6. Engine Cranking: The starter motor, now energized, begins to turn the engine crankshaft, allowing the pistons to move and ignite the fuel.

Signs of a Faulty Solenoid

Like any electrical component, solenoids can experience wear and tear, eventually leading to malfunctions. Here are some signs that your solenoid might be failing:

1. Clicking Noise: If you hear a clicking noise when you turn the key but the engine doesn’t crank, it could indicate a problem with the solenoid. This clicking sound is the solenoid’s electromagnet attempting to pull the plunger, but failing to engage fully.

2. No Crank, No Click: If you don’t hear any clicking noise at all and the engine refuses to crank, this is a strong indication of a faulty solenoid.

3. Battery Draining: A faulty solenoid might continuously draw current from your battery even when the engine isn’t running, eventually draining it.

Diagnosing a Solenoid Issue

If you suspect a faulty solenoid, you can test it with a few simple steps:

  1. Disconnect the Battery: Always disconnect the battery before working on any electrical component.
  2. Check for Power: Use a multimeter to check if power is reaching the solenoid when the key is turned to the “start” position.
  3. Test the Solenoid: Disconnect the wires leading to the solenoid and use a jumper cable to connect the positive terminal of the battery directly to the solenoid’s terminal. If the solenoid clicks and the plunger moves, it indicates the solenoid is working correctly. If it doesn’t click, the solenoid is faulty.
  4. Visual Inspection: Also, check for any signs of damage, corrosion, or loose connections on the solenoid.

Replacing a Faulty Solenoid

If your solenoid test reveals a problem, it’s time for a replacement. The process of replacing a solenoid is relatively simple:

  1. Locate the Solenoid: The solenoid is usually located near the starter motor, often attached to the frame of the lawn mower.
  2. Disconnect the Wires: Disconnect the wires leading to the solenoid.
  3. Remove the Solenoid: Depending on the model, you may need to loosen some bolts or screws to remove the solenoid.
  4. Install the New Solenoid: Attach the new solenoid in the same location as the old one, ensuring the wires are connected correctly.
  5. Reconnect the Battery: Reconnect the battery and test the engine to confirm the solenoid is functioning properly.

Solenoid Maintenance: A Preventive Measure

While replacing a faulty solenoid is fairly straightforward, preventing problems in the first place is always preferable. Here are a few tips for solenoid maintenance:

1. Keep it Clean: Regularly clean the solenoid and its surroundings to prevent dirt and debris from accumulating.

2. Check for Corrosion: Periodically inspect the solenoid for any signs of corrosion and clean it if necessary.

3. Use Quality Battery: A strong battery ensures enough power for the solenoid to function correctly.


The solenoid, though often overlooked, plays a critical role in the starting mechanism of a lawn mower. Understanding its operation, common problems, and troubleshooting steps empowers you to handle basic maintenance and repair tasks, saving you time, money, and potential frustration in the long run. By taking care of your lawn mower’s solenoid, you ensure a smooth and trouble-free mowing experience, keeping your lawn in tip-top shape.

Frequently Asked Questions

How does a solenoid work on a lawnmower?

A solenoid is a type of electromagnet that is commonly used in lawnmowers to engage the starter motor. It is a simple device consisting of a coil of wire wrapped around a metal core. When electricity flows through the coil, it creates a magnetic field that draws a metal plunger into the coil. This plunger is connected to the starter motor, so when the solenoid is activated, it pulls the starter motor into engagement with the engine’s flywheel.

This process allows the starter motor to turn the engine crankshaft and start the engine. The solenoid is typically activated by a starter switch, which completes the electrical circuit when the key is turned to the start position. When the engine starts, the solenoid is deactivated, releasing the starter motor and allowing it to disengage from the flywheel.

Why is a solenoid used in a lawnmower?

A solenoid is used in a lawnmower to engage the starter motor because it provides a simple and reliable way to activate the motor when needed. It is also relatively inexpensive to manufacture and maintain. Without a solenoid, the starter motor would be constantly engaged with the flywheel, which would drain the battery and prevent the engine from starting. The solenoid serves as a necessary bridge between the starter motor and the ignition system, allowing for efficient and controlled engagement of the starter motor during the starting process.

What happens if the solenoid is faulty?

If the solenoid is faulty, it may not be able to engage the starter motor properly. This can cause the engine to crank slowly or not start at all. A faulty solenoid can also cause the starter motor to stay engaged after the engine has started, which can damage the starter motor or battery. In these cases, the solenoid will need to be replaced.

How do I know if my lawnmower solenoid is bad?

A bad lawnmower solenoid can exhibit several symptoms, including a slow cranking engine, a clicking noise when you try to start the engine, or no starting at all. If your lawnmower is experiencing any of these issues, it’s likely the solenoid is faulty and needs to be replaced. A simple test can be conducted by jumping the solenoid directly to the battery; if the starter motor engages, then the solenoid is likely faulty.

Can I replace a lawnmower solenoid myself?

Replacing a lawnmower solenoid is a relatively simple procedure that can be done by most DIYers. You will need to disconnect the battery cables, remove the old solenoid, and install the new one. You will also need to connect the wiring to the new solenoid.

However, if you are not comfortable working with electrical components, it’s always best to consult a qualified mechanic.

How do I maintain a lawnmower solenoid?

The solenoid on your lawnmower doesn’t typically require much maintenance. However, there are a few things you can do to help keep it in good working order. First, ensure the battery connections are clean and free from corrosion. Second, check the solenoid for any signs of damage or wear, such as loose wires or a damaged plunger.

If you notice any problems, it’s best to replace the solenoid.

What are the different types of lawnmower solenoids?

There are two main types of lawnmower solenoids: single-coil and double-coil. Single-coil solenoids are the most common type and have a single coil that activates the plunger. Double-coil solenoids have two coils: one for engaging the starter motor and the other for disengaging it.

Double-coil solenoids are generally considered to be more reliable than single-coil solenoids because they have a separate coil for disengaging the starter motor, which helps to prevent the starter motor from being damaged.

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