Symptoms Of Bad Ignition Coil On Lawn Mower

You love your lawn; your lawn mower is your trusty sidekick, keeping it lush and beautiful.

But what happens when your mower starts acting up, leaving you puzzled and your lawn unfinished? The culprit might be a bad ignition coil. 

Understanding what’s going on under that mower hood is essential for DIY enthusiasts and anyone who takes pride in their outdoor space. 

In this guide, you’ll learn the main signs showing that your mower’s ignition coil might fail.

We’ll also tell you why this happens and what you can do to fix it. It’s all easy to understand, so you can return to making your lawn look great.

Symptoms of Bad Ignition Coil on Lawn Mower

If your lawn mower struggles to start, stalls randomly, or shows uneven engine performance, you might be dealing with a bad ignition coil. This vital component generates the spark needed to power your mower. When it fails, it can lead to fuel inefficiency, engine misfires, and even oil leaks. Knowing the symptoms can help you fix issues early.

Understanding the Ignition Coil’s Function

The lawn mower’s ignition coil is like the heart of its engine. It has a significant job: it takes low power from the battery and turns it into a big spark. This spark plug fires the fuel in your engine, which allows your mower to run.

Imagine starting a campfire; you need that first spark to get the flames going. If your ignition coil isn’t working well, your mower will have difficulty starting or might not run smoothly.

So, keeping this part in good shape is key to having a mower that works when you need it.

Symptoms of bad ignition coil on lawn mower

7 Key Symptoms, Causes, and Remedies

1. Unpredictable engine stalling

Is your lawn mower stopping while you’re using it? It can be annoying and is often a sign of bad ignition coil symptoms in lawnmowers.

When your engine stalls, a few things could be going wrong. Lawn mower ignition coils might be getting too hot and worn out.

Sometimes, the wires that connect parts might be damaged. There’s also a part called a ‘kill switch’ that can stop working right. Bad fuel or an old spark plug boot could be a problem, too.


  • Replace the Kill Switch, Spark Plug, or Coil: If any of these parts are the problem, getting a new one is often the best fix.
  • Secure Wiring Connections: Loose or damaged wires can cause stalling. Make sure all wires are tightly connected and fix any that look worn out.
  • Drain and Replace Fuel: If your fuel is old or dirty, empty the fuel tank and put in fresh fuel.
  • Cool Down Coil, Replace if Necessary: If the ignition system is too hot, let it cool down before you start the mower again. If it keeps getting hot, you may need a new one.

2. Start-up failures

Ever pull the start cord on your lawn mower, and nothing happens? It’s frustrating, right? Start-up failures are often linked to a dodgy ignition coil.

A start-up failure can happen for several reasons. The coil might be old and worn out. Another possibility is the faulty ignition switch, like your mower’s “on” button.

Cold weather can make it hard for your mower to start, too. If the insulation around the coil is damaged, that’s another reason it might not start.


  • Spark Test, Replace Coil: Perform a simple spark test. If there’s no spark, you need a new coil.
  • Check Ignition Switch: If turning the key or pressing the start button doesn’t do anything, the ignition module might be broken and needs replacing.
  • Warm-Up Mower: If it’s chilly outside, try moving your mower to a warmer spot or wait for the temperature to rise before starting it again.
  • Replace Coil: If you find out the coil is damaged or worn out, it’s time for a new ignition coil

3. Sporadic engine behavior

Does your lawn mower run inconsistently? Sporadic engine behavior can throw off your lawn care routine, and it’s often a clue that something’s up with the ignition coil.

There are a few reasons why your engine might act this way. The coil connections might be loose or broken, coming on and off as you mow. 

Overheating of the coil is another common cause. Voltage issues in the mower’s electrical system or damaged coil windings could also be at fault here.


  • Secure Coil Connections: Make sure the coil is well connected. Tighten any loose connections to ensure a consistent spark.
  • Let Engine Cool, Replace Coil: If the coil is overheating, allow it some time to cool down before you start the mower again. If the problem persists, consider replacing the coil.
  • Check Electrical System: Electrical problems can also cause inconsistent engine behavior. Double-check the wiring and voltage to make sure everything’s in order.
  • Replace Coil: If the coil is damaged or its windings are frayed, a new coil is likely your best bet.
Symptoms of bad ignition coil on lawn mower

4. Frequent engine misfires

If your lawn mower’s engine is misfiring or ‘skipping,’ you’ll notice.

It makes mowing your lawn a choppy, inefficient task and often indicates that your ignition coil or another component needs attention.

There are several reasons why misfires can happen. A weak spark is a big red flag, which means your coil or spark plugs aren’t doing their job well.

Fuel supply issues like clogs or leaks can also cause misfires. An obstructed air filter or poor-quality fuel are other common culprits.


  • Replace Spark Plug or Coil: If the spark is weak, changing the spark plug or the coil usually solves the problem.
  • Check Fuel Lines and Filter: Make sure the fuel can flow freely. Look for clogs or damage in the fuel lines and filter, and fix them if needed.
  • Clean or Replace Air Filter: A dirty air filter can starve your engine of the air it needs. Cleaning or replacing the filter can often fix the misfiring issue.
  • Replace Fuel: If your fuel is old or contaminated, replacing it with fresh, high-quality fuel can make a difference.

5. Worsening fuel efficiency

Notice you’re refilling the gas tank more often than usual? Your mower’s dwindling fuel efficiency can be frustrating and costly, often tied to issues with the ignition coil.

Several factors can contribute to worsening fuel efficiency. A weak spark could mean that fuel isn’t burning well.

Incorrect ignition timing can also throw off fuel consumption. A clogged carburetor means your mower must work harder, using more fuel.

Wear and tear on the coil’s lamination could hurt your mower’s fuel efficiency.


  • Replace Coil: A new coil is usually the answer if the coil shows signs of wear or damage, especially in the laminations.
  • Adjust Ignition Timing: Incorrect timing can make your engine less efficient. Adjusting the ignition timing solves the problem.
  • Clean Carburetor: A dirty carburetor can obstruct fuel flow, forcing your engine to work harder. Cleaning it can help your mower run more efficiently.
  • Replace Coil: If you’ve tried the above fixes and still have issues, it might be time for a new ignition coil.

6. Hiccups in engine cranking

When you’re ready to tackle your lawn, the last thing you want is an engine that hesitates or struggles to start.

If you’re experiencing hiccups while trying to crank the engine, it’s a sign that something is off.

There could be several factors at play regarding engine cranking issues. A weak spark is a key suspect, often pointing to ignition coil troubles.

Battery problems can also make it tough for the engine to kick in. Poor grounding could lead to inconsistent electrical flow, and damaged flywheel magnets can mess with the engine’s starting mechanism.


  • Use a Spark Tester, Replace Coil: If you suspect a weak spark, a spark tester can confirm your doubts. If the spark is indeed weak, replacing the coil should resolve the issue.
  • Check and Replace Battery: A failing battery could make cranking difficult. Test your battery and replace it if it’s not holding a charge.
  • Correct Grounding Issues: Ensure all connections are secure and properly grounded for consistent electrical flow, which is crucial for cranking.
  • Replace Flywheel or Magnets: If the flywheel or its magnets are damaged, replacing them will solve cranking problems.

7. Visible oil leakage 

If you see oil under your mower, that’s a sign of trouble. This issue may not be about the ignition coil, but it’s big and needs fixing.

Oil leaks can happen for several reasons. One common cause is bad gaskets. Gaskets are like seals between engine parts. Over time, they can wear out and let oil leak.

Another reason could be that the engine is old and worn out, making it leak oil, too. The engine block might crack in more serious cases, leading to a big oil leak.

Sometimes, the issue is simple, like a loose drain plug or oil filter that needs tightening.


  • Replace Gaskets: If the leak is coming from a worn or damaged gasket, replacing it should seal the deal.
  • Engine Health Check: Run a comprehensive health check of the engine to identify any wear and tear that might be causing leaks.
  • Repair or Replace Engine Block: If there’s a crack in the engine block, you may need to repair or replace the entire engine, depending on the severity.
  • Tighten Drain Plug or Replace Oil Filter: Sometimes, tightening the drain plug or replacing the oil filter is enough to stop the leak.
Symptoms of bad ignition coil on lawn mower

Summary Table of Lawn Mower Coil Troubleshooting

Unpredictable StallingOverheating, faulty wiringReplace coil, secure wiring
Start-up FailuresWorn coil, bad ignition switchReplace the coil, check the switch
Sporadic Engine BehaviorIntermittent connectionsSecure connections, replace coil
Engine MisfiresWeak spark, clogged air filterReplace the spark plug, clean the filter
Poor Fuel EfficiencyTiming issues, worn coilAdjust timing, replace coil
Engine Cranking HiccupsWeak spark, bad batteryUse spark tester, replace battery
Oil LeakageBad gaskets, cracked engineReplace gaskets, fix or replace engine

Brand Specific

Briggs and Stratton bad coil symptoms

  • Struggle to Start: If your mower takes too long or doesn’t start, this could mean a faulty ignition coil.
  • Engine Stalls: Experiencing sudden stops, especially when the mower is warm, may indicate a coil issue.

John Deere ignition coil problems

  • Inconsistent Engine: If your John Deere mower won’t start or the engine is running unevenly, this could indicate an ignition coil problem.
  • Misfires: Jolts and shaky runs could signify a malfunctioning coil.

Cub cadet coil problem

  • Hard Starts: If your Cub Cadet mower is hard to start, the ignition coil may malfunction.
  • Engine Hiccups: Sporadic stops and starts during use can point to a failing ignition coil.

Husqvarna ignition coil problems

  • Finicky Starts: If your Husqvarna mower doesn’t start easily, this could be a symptom of a faulty coil, a common Husqvarna mower problem.
  • Stalling: If the mower stops running suddenly while you’re mowing, this may point to a bad coil.
  • Fuel Inefficiency: If you’re filling up the gas more often than usual, this could indicate a problem with the ignition coil.

How to Diagnose a Malfunctioning Ignition Coil

Diagnosing a faulty ignition coil doesn’t have to be complicated. Here are some steps to help you identify the problem:

  • Observe Symptoms: Look for issues like a struggling engine start, frequent stalling, or engine misfires. These are usually the first signs of a coil problem.
  • Spark Test: Detach the spark plug and hold it close to a metal surface. Turn the engine over and see if a spark appears. No spark? Your coil may be to blame.
  • Use a Multimeter: Switch your multimeter to measure resistance. Check the readings between the coil’s electrical connections. Unusual numbers often mean a bad coil.
  • Engine Behavior: Notice if your engine stalls unexpectedly or acts weird. These could be indicators of a faulty coil.
  • Consult an Expert: Getting a professional opinion is wise when in doubt. A quick check-up can confirm if your ignition coil needs replacement or not.

Steps for Ignition Coil Replacement

When to replace

Consider replacing your ignition coil when you notice symptoms like poor fuel efficiency, frequent engine stalls, or starting issues.

A failing coil can lead to more significant problems, so addressing the issue is better to avoid further damage.

Replacement instructions

  • Take off the Old Ignition Coil: First, disconnect your mower’s battery. Then, locate the lawn mower ignition coil and disconnect the wires. Unscrew and remove the old coil.
  • Conduct a Coil Functionality Test: Before installing the new coil, you may want to test it with a multimeter to ensure it’s functional.
  • Apply Lubrication and Re-insert the New Coil: Lubricate the new coil’s contacts to help ensure a smooth installation. Now, align and place the new coil in position, then screw it in securely.
  • Conclude the Installation: Reconnect the electrical wires and the battery. Make sure all connections are secure before trying to start your mower.

Safety Precautions During Installation

  1. Disconnect the Battery: Always start by disconnecting the battery to avoid accidental starts or electrical shocks.
  2. Wear Protective Gear: Wear gloves and safety goggles to protect your hands and eyes.
  3. Ventilate the Area: If you’re working in a closed space, ensure it’s well-ventilated to avoid inhaling fumes.
  4. No Open Flames: Avoid open flames or cigarettes, as you’ll work near fuel and oil.
  5. Use Proper Tools: Make sure to use the right type and size of tools for the job to avoid damaging parts.
  6. Read the Manual: Consult your mower’s manual for specific safety guidelines or instructions.
  7. Double-Check Connections: Ensure all wires and parts are securely placed before reconnecting the battery.
  8. Test in a Controlled Environment: Once installed, initially run the mower in a controlled, open space to ensure it’s working correctly.


What makes a lawn mower coil go bad?

A lawn mower coil can fail due to overheating, bad wiring, or plain wear and tear. Other times, inner parts like the coil windings can get damaged. These problems can lead to poor starting or even complete engine failure, disrupting your ability to take care of your lawn on time.

How to test an ignition coil on a lawn mower

To check a lawn mower’s coil, use a spark tester. Disconnect the spark plug wire and connect the tester. Turn the mower’s engine. Your coil is likely only good if you see a spark in the tester. This simple test helps diagnose coil issues and keeps your mower running smoothly.


Understanding the signs of a bad ignition coil can save you time, money, and the frustration of dealing with a faulty lawn mower.

Knowing how to diagnose and fix these issues extends the life of your mower and ensures a smooth and efficient operation.

Brands like Briggs and Stratton, John Deere, Cub Cadet, and Husqvarna have specific symptoms, but the core issues often remain the same.

Always take safety precautions and refer to your mower’s manual for model-specific guidelines. Staying informed will make your lawn care routine more reliable and stress-free.