Is Your Lawn Mower Coil Dead? How to Test It and Know for Sure!

The hum of a lawn mower engine is a familiar summer soundtrack, but what happens when that hum turns into a sputtering cough, leaving your grass untrimmed and your patience wearing thin? One common culprit behind a lawn mower’s woes is a faulty ignition coil. This unsung hero is responsible for delivering the spark that ignites the fuel-air mixture, bringing your mower to life. If your lawn mower isn’t firing up, a faulty coil could be the culprit.

This article will guide you through the process of testing your lawn mower coil, helping you diagnose the problem and determine whether it needs replacing. We’ll explore the symptoms of a bad coil, explain the different types of coils, and walk you through the simple steps for testing it using a multimeter. Whether you’re a seasoned mechanic or a weekend DIY enthusiast, this guide will empower you to troubleshoot your lawn mower and get back to enjoying your manicured lawn.

A faulty ignition coil can be a common culprit behind a lawn mower’s refusal to start. The coil acts like a transformer, converting low-voltage battery power into high-voltage electricity that sparks the spark plug. When the coil fails, it can prevent the spark plug from firing, leaving your mower unable to start.

Recognizing the Symptoms of a Faulty Ignition Coil

Before you start testing, it’s helpful to understand the signs that suggest your lawn mower coil might be on the fritz. These symptoms can indicate a problem with the coil or another part of the ignition system, but testing the coil is a good starting point for troubleshooting.

Common Signs of a Bad Ignition Coil

  • No Spark: The most obvious symptom is a complete lack of spark at the spark plug. If you’ve ruled out other potential causes, such as a dead battery or a faulty spark plug, a bad coil is a prime suspect.
  • Engine Cranks But Doesn’t Start: If your lawn mower turns over but refuses to fire up, this is a common sign of an ignition problem, and the coil could be the culprit.
  • Intermittent Engine Stalling: A faulty coil can sometimes deliver a weak spark, causing the engine to sputter and stall intermittently. This can be particularly frustrating, as it may appear to work fine at times but then suddenly die.
  • Difficult Starting: If your lawn mower is taking an unusually long time to start, especially in warm weather, a weakened coil could be the reason.

Understanding the Different Types of Ignition Coils

Modern lawn mowers utilize various types of ignition coils, each with its own design and function.

1. Single Coil Systems

These systems, found on older lawn mowers, use a single coil to provide the spark for all cylinders. They typically consist of a primary and secondary winding, encased in a protective housing.

2. Multiple Coil Systems

Newer lawn mowers often employ multiple coils, with a separate coil for each cylinder. This allows for more precise spark delivery and improved engine performance.

3. Electronic Ignition Systems

Some lawn mowers feature electronic ignition systems that incorporate a control module or ignition control unit (ICU). These systems manage spark timing and ignition timing electronically, often relying on a separate pickup coil to sense the engine’s position.

Testing the Ignition Coil with a Multimeter

Now that you understand the signs of a faulty coil and the different types available, it’s time to roll up your sleeves and test the coil. This process requires a basic understanding of electrical circuits and a multimeter, which can be purchased from most hardware or automotive stores.

Essential Tools for the Job:

  1. Multimeter: A multimeter is essential for testing the coil’s resistance and continuity. It measures electrical values such as voltage, resistance, and current.
  2. Safety Glasses: Protect your eyes from potential sparks or debris.
  3. Gloves: Rubber-coated gloves help prevent electric shock.
  4. Wire Connectors: Optional but helpful for connecting the multimeter to the coil wires.

Step-by-Step Testing Procedure

  1. Disconnect the Spark Plug: Disconnect the spark plug wire from the spark plug to prevent accidental ignition.

  2. Locate the Ignition Coil: Identify the coil on your lawn mower. It’s typically located near the engine, often mounted to the engine block or the frame.

  3. Locate the Coil Wires: The coil will have two or more wires connected to it.

  4. Primary Wire: This wire connects to the ignition system’s switch or control unit.
  5. Secondary Wire: This wire connects to the spark plug.

  6. Set the Multimeter to Resistance Mode: Select the ohms (Ω) setting on your multimeter.

  7. Test the Primary Winding:

  8. Connect the red probe of the multimeter to the primary wire.
  9. Connect the black probe to the other end of the primary wire.
  10. The resistance reading should fall within the manufacturer’s specifications for your particular coil. If the reading is too high, infinite, or zero, the primary winding is likely faulty.

  11. Test the Secondary Winding:

  12. Connect the red probe to the secondary wire (the wire that goes to the spark plug).
  13. Connect the black probe to the other end of the secondary wire.
  14. The resistance reading should also fall within the manufacturer’s specifications.

Note: Some coils use a single wire for the secondary winding, which would connect to the spark plug. In this case, you’ll need to connect the probe to the single wire and the other probe to the coil’s case or ground.

Interpreting the Test Results

  • Normal Resistance: If the multimeter displays resistance readings within the specified range for your coil, the coil is likely functioning properly.
  • High Resistance: A very high resistance reading indicates a possible open circuit in the coil winding, preventing proper current flow.
  • Zero Resistance: A zero resistance reading suggests a short circuit in the coil winding, which could also prevent the coil from functioning correctly.

Replacing the Ignition Coil

If your test results indicate a faulty coil, replacing it is the most effective solution. Here’s a general guide for replacing a lawn mower ignition coil:

  1. Disconnect the Battery: Disconnect the negative terminal of your lawn mower battery to prevent accidental electric shock.

  2. Remove the Old Coil: Locate the mounting screws or clips that hold the coil in place and carefully remove it. Take note of how the wiring is connected.

  3. Install the New Coil: Position the new coil in the same location as the old one, making sure it’s properly aligned. Secure it with the mounting screws or clips.

  4. Connect the Wires: Connect the primary and secondary wires to the new coil.

  5. Reconnect the Battery: Reconnect the battery’s negative terminal.

Maintaining Your Lawn Mower Coil

While a faulty coil may need replacement, regular maintenance can help prolong its lifespan and prevent premature failure.

  1. Keep the Coil Clean: Regularly clean the coil and its surrounding area with a brush or compressed air to remove dirt, debris, and moisture.
  2. Check the Connections: Ensure that the wires connected to the coil are securely attached and free of corrosion.
  3. Inspect the Spark Plug: A faulty spark plug can damage the coil. Inspect the spark plug for wear and tear, and replace it if necessary.


By understanding the symptoms, testing procedures, and maintenance tips outlined in this article, you can confidently troubleshoot and repair your lawn mower’s ignition coil. Armed with a multimeter and a bit of patience, you’ll be back to enjoying a perfectly manicured lawn in no time! Remember, if you’re unsure about any part of the process or are dealing with a more complex electrical issue, consult with a qualified mechanic.


Q1: What is a lawnmower coil and why is it important?

A lawnmower coil is a crucial component of the ignition system that converts low voltage from the battery into high voltage to spark the spark plug. It’s essentially the transformer that powers the ignition system, allowing the engine to fire up and run smoothly. Without a functioning coil, the spark plug won’t receive the necessary energy to ignite the fuel-air mixture, preventing your lawnmower from starting or running properly.

A faulty coil can cause a variety of problems, including engine misfiring, difficulty starting, and even complete engine failure. Identifying a dead coil early can save you significant frustration and potential repair costs.

Q2: How do I know if my lawnmower coil is dead?

There are several signs that indicate a faulty coil. Firstly, if your lawnmower is struggling to start or won’t start at all, a dead coil could be the culprit. Additionally, if you notice your engine misfiring or running rough, it’s another indication that the coil might be failing. Lastly, if your lawnmower seems to have lost power or is unable to maintain a consistent speed, a faulty coil could be the cause.

To confirm if the coil is truly dead, it’s best to test it with a multimeter. You can follow the steps outlined in the article to check the coil’s resistance and verify if it’s within the acceptable range for your specific model.

Q3: What tools do I need to test my lawnmower coil?

Testing your lawnmower coil requires a few basic tools that are readily available at most hardware stores. First and foremost, you’ll need a multimeter, which is an essential tool for any DIY mechanic. You’ll also need a few simple tools for accessing the coil, such as a screwdriver, a socket wrench, and possibly a wire brush for cleaning any corroded terminals.

Having a service manual for your specific lawnmower model can be incredibly helpful, as it will provide detailed diagrams and instructions for locating and testing the coil.

Q4: How do I test the resistance of my lawnmower coil?

Testing the resistance of your lawnmower coil involves using a multimeter to measure the electrical resistance between the coil’s terminals. Start by disconnecting the coil from the spark plug wire and ensuring that the engine is off and the spark plug is grounded. Set your multimeter to the ohms setting and connect the probes to the coil’s terminals, typically labeled as “primary” and “secondary.”

The resistance reading should fall within a specific range for your lawnmower model, which you can find in the service manual or online. If the resistance reading is outside this range, it’s highly likely that the coil is faulty.

Q5: What if the coil is dead? How do I replace it?

Replacing a dead lawnmower coil is generally a straightforward process that you can often handle yourself. First, you’ll need to obtain a replacement coil that’s specifically designed for your lawnmower model. You can purchase a new coil from a local hardware store or online retailer.

Once you have the new coil, locate the old coil and disconnect it from the spark plug wire and any other connected wires. Carefully remove the old coil from its mounting location and install the new coil in its place. Ensure that all connections are secure and then reconnect the spark plug wire and any other wires.

Q6: How do I know if the new coil is working properly?

After replacing the lawnmower coil, it’s essential to confirm that the new coil is functioning correctly. You can do this by performing a simple spark test. Connect a spark plug wire to the new coil, and ground the spark plug against a metal surface.

Start the lawnmower and observe the spark plug. You should see a strong blue spark jumping across the gap of the spark plug. If you see a weak or nonexistent spark, it might indicate that the new coil is faulty or that there’s another issue with the ignition system.

Q7: Can I avoid replacing the coil? Are there any alternatives?

While replacing the coil is the most effective solution for a dead coil, there are some temporary solutions that you can try before resorting to a replacement. One option is to clean the coil terminals and ensure that they are making good contact. You can also try cleaning the spark plug to remove any carbon buildup, which can hinder the spark.

However, these solutions are only temporary and may not address the root cause of the problem. If you continue to experience issues with your lawnmower, replacing the coil is the most reliable solution.

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