It’s usually bad timing when your John Deere mower won’t start. You can bring your lawn mower to the dealership to be fixed, but during the busy season, you may not get your lawn mower back for a week or two.

Your lawn doesn’t just stop growing when your mower is down so what can you do to get it running again? There are some items you can check before you bring the mower to a professional.

A John Deere lawn mower may not start because of an issue in the fuel system, a clogged air filter, a dirty carburetor, a bad battery, a safety switch, bad spark plugs, or a faulty ignition switch. A problem in the charging system or ignition coil can also be the culprit of your starting problem. 

I have put together a list of items that can cause starting issues in your John Deere gas-powered lawn mower. Many of these items can be checked and easily fixed so you can have your lawn looking good in no time!

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Reasons Why Your John Deere Mower Won’t Start 

1. No Gas in Your John Deere Mower Fuel Tank 

This may seem like a no-brainer, but to my surprise, I have found it to be the reason why several of my customers’ mowers won’t start. Sometimes you forget the simple things like adding fuel to your mower or you may have not realized you developed a fuel leak.

Fix: Fill your fuel tank with fresh gasoline. I write more about the correct fuel for your gas John Deere lawn mower here. Add diesel fuel if you are running a diesel-powered mower.

2. Bad or Old Fuel in Your John Deere

Fuel that doesn’t get used right away becomes old and stale over time. Gas only has a 30-day shelf life before it begins to break down and becomes less effective.

The ethanol added to today’s gasoline draws moisture to the fuel. When this moisture evaporates, a residue is left behind that clogs the fuel system. 

Always use fuel quickly.  If you are unable to consume the fuel within 30 days, you need to add a fuel additive to stabilize it. 

Fix: Remove the old fuel using a fuel siphon pump, and add fresh fuel with a fuel additive to clean the fuel system and reduce moisture. I use Sea Foam Motor Treatment in my fuel. 

3. Faulty John Deere Fuel Cap 

Your fuel cap is vented by design.  When your cap is broken or plugged and the cap no long vents, a vacuum is formed in the fuel tank. The vacuum prevents fuel from leaving the fuel tank so your John Deere mower won’t start.

To narrow down a starting problem to the fuel cap, remove the cap and try to start your mower. If it starts and runs fine, reinstall the fuel cap and allow your John Deere to continue to run.

You are waiting for the mower to begin to run sluggishly and shut off after running for a while. If it does, you should be able to remove the cap again and start it.

This is how you determine you have a problem with the fuel cap. Do not allow dirt to get into the fuel tank when the cap is removed.

Fix: Replace the old cap with a new fuel cap. You can find one on Amazon or visit your local John Deere dealership. 

4. John Deere Mower has a Bad Spark Plug or Loose Connection 

You may have a bad spark plug connection or the spark plug may be damaged. A plug that is excessively dirty can foul out causing your engine to misfire.

Remove your spark plug and inspect it for signs of dirt, carbon buildup, or a cracked porcelain insulator. A loose connection or a plug that isn’t gapped correctly can also cause starting issues.

Fix: Replace a very dirty or damaged spark plug with a new spark plug. Make sure to gap them according to your manufacturer’s specifications. 

If you find your spark plug is in good condition, but has a dirty tip, use a wire brush to clean it and reuse it.

5. John Deere Air Filter is Plugged

Clean air is crucial to the performance of your John Deere engine. When the air filter is excessively dirty, the engine can’t get air and it is essentially being suffocated. 

This can develop into a larger problem causing extensive engine damage if not addressed right away. It’s good practice to replace your air filter annually and clean it several times throughout the mowing season.

If you are mowing in dusty conditions, you will have to check, clean, and replace your air filter more often. A plugged air filter will prevent your John Deere mower from starting.

Fix: Follow these steps to clean or replace your John Deere paper air filter:

• Clean your paper air filter by removing it from the air filter housing. Be careful not to let any dirt get into the air intake.  
• Tap the filter against a solid surface to remove excess dirt. 
• Hold the filter up to a light source. What you are doing is checking to see if light is shining through the paper element.
  • If you cannot see light, you must replace the air filter with a new one.
  • If you can see light through the filter and it’s not dark, covered with oil or damaged, go ahead and reuse it.
• Insert the air filter into the housing and reattach the air filter cover.

For information on other types of air filters read my article here. 

6. Bad John Deere Fuel Pump 

Most John Deere lawn mowers use a vacuum fuel pump to pump gas to your carburetor when the fuel tank sits lower than the carburetor. The fuel pump has 3 ports on it.

There is an inlet port and outlet port where the fuel passes in and out of the pump. The third port is attached to a fitting to use pressure of the crankcase to push fuel to the carburetor

FIX: First, inspect your vacuum fuel pump for cracks. If you see fuel outside of the fuel pump or cracks in the pump, the pump will no longer be able to work as designed. It must be replaced.

Second, you will want to make sure you are getting fuel from the fuel tank to the fuel pump. Turn off the fuel valve or use pinch pliers to crimp the fuel line and stop fuel flow.

Disconnect the line from the fuel pump inlet port and place it in a container that sits lower than the fuel tank. Unclamp the fuel line or turn on the fuel valve and check to make sure fuel is flowing out of the tube into the container. 

If you are not getting fuel, your fuel troubles exist before the fuel pump. You will need to check for blocked fuel lines or a plugged fuel filter. 

Third, if your fuel pump appears to be in good condition, and you have verified you are getting fuel to the fuel pump, you will need to verify your fuel pump is pumping fuel to the carburetor. Reinstall the first fuel line you took off by connecting it to the fuel pump inlet port.

Next, remove the fuel line from the carburetor. Place the tube in a container, start the lawn mower, and watch the end of the fuel line to make sure fuel is being pumped out of the fuel line into the container. You should have a steady flow or pulsating flow of fuel coming out of the fuel line. 

Replace your fuel pump if it fails to provide a flow of fuel out of the outlet tube or if you find the fuel pump is damaged or leaking.

7. Plugged John Deere Fuel Filter 

A fuel filter can become plugged when running dirty or old fuel. The filter is designed to screen the fuel to prevent dirt and other contaminants from entering the fuel system. A plugged filter will restrict the amount of fuel available to the engine preventing it from starting.

Fix: Replace a plugged fuel filter with a new filter. Pay attention to the arrow on the side of the fuel filter when installing it. The filter must be installed with the arrow pointed in the direction of the fuel flow.

8. Blockage in the John Deere Fuel Line 

Old fuel can leave gummy deposits that can become lodged in your John Deere mower’s fuel line. This affects the amount of fuel available to start and run your John Deere.

Use the fuel shut-off valve or crimp the fuel line to stop and start fuel flow while checking each section of the fuel line for a blockage. 

Fix: Once you identify a section of the fuel line that is restricted with a clog, remove the fuel line from your John Deere mower. Make sure your fuel flow is stopped before removing the line. Spray carburetor cleaner into the tube to loosen the clog.

Blow compressed air through the line to remove the clog. Repeat with spraying carburetor cleaner and blowing air as needed until the line is no longer blocked. Install a new fuel line if you are unable to remove the clog or if your fuel lines are dry, brittle, and beginning to crack.

9. Clogged & Dirty John Deere Carburetor 

The carburetor is essential to your engine running because it regulates the amount of fuel mixed with air to create a combustion.

The John Deere lawn mower carburetor can become dirty clogging components and preventing them from functioning properly. This will prevent the flow of gas needed to start the mower.

Fix: Clean the carburetor by taking it apart and using carburetor cleaner to clean the carburetor including the float bowl and needle. You can find steps for cleaning your John Deere carburetor in this article. 

You may have to replace or rebuild the carburetor if it appears to be in very bad condition or if cleaning does not solve your carburetor problem.

10. John Deere Has a Bad Battery or Loose Terminals 

Your John Deere lawn mower won’t start when the battery is dead. Make sure your battery cables are secure and the connections are not showing signs of corrosion. 

Clean the terminals if they are showing signs of corrosion. Use a baking soda mix (2 cups of water and 3 heaping tbsp. of baking soda) and a wire brush.

Fix: Test your battery with a multimeter. You will want a reading of about 12.7 volts. Place on a charger to charge your battery if your reading is less than 12.7 volts.

Read more about the steps and items needed to charge your battery here. If your battery does not hold a charge, you will need to replace it with a new battery. 

11. Bad John Deere Safety Switch

Your lawn mower may use several safety switches in its operator’s presence control system. The switches are meant to keep you safe while operating the mower.

There is a switch designed to kill the engine if the operator leaves the seat when the mower deck is engaged in addition to other safety switches.

Refer to your operator’s manual for all safety devices used on your mower. A bad switch can cause your John Deere mower not to start. 

Fix: You can temporarily bypass the safety switch to identify a bad switch. A multimeter can also be used to help identify a bad switch. Never operate a mower without a good safety switch or when the switch is bypassed. Many people get injured by mowers annually by rolling them or falling off the mower. 

It’s important to always have safety switches installed and working on your equipment. You never know when you’re going to need them most.

12. John Deere Has a Bad Ignition Switch 

You insert the key into your ignition switch and turn it only to find nothing happens. Your John Deere mower won’t start. The ignition switch can be the culprit.  You can check the switch using a multimeter.

Fix: Replace the ignition switch if you find it is bad.

13. Bad Ignition Coil on Your John Deere Mower

The ignition coil provides voltage to the spark plug so it can fire and start the engine. The engine will not start if the spark plug isn’t able to fire.  

Fix: After you verified your spark plug is in good condition, check the continuity of your ignition coil using an ohmmeter. Replace the ignition coil if you find a break in the continuity. 

14. Bad Starter Solenoid on Your John Deere Mower

A lawn mower solenoid is an electromagnetic switch that is like an on-off switch that actuates the starter motor to turn over the engine. A click or hum when turning your ignition key is an indication to check your solenoid.

Another indication your John Deere mower solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.

Fix: Test your John Deere mower solenoid by following the steps here. Replace your solenoid if it is found to be bad.

15. John Deere Mower’s Charging System is Not Charging 

While the charging system isn’t the main reason your John Deere lawn mower won’t start, it can contribute to a weak battery that prevents the mower from starting.

When the charging system fails to charge the battery, the battery may not be able to start the mower the next time you go to use it.

A bad stator or alternator can be the problem along with several other electrical parts. Read this article to test your charging system here using an ohm meter. 

Fix: If you find the problem is in your charging system, have a small engine mechanic identify the actual cause of the failure.

It could be several different items and you don’t want to start guessing at the cause of the problem. Throwing parts at your John Deere mower gets pretty expensive. 

16. Incorrect Operating Procedure When Starting Your John Deere 

There are different safety procedures taken by John Deere when starting and operating your lawn mower that will shut off the mower. For example, when you get off your zero-turn mower with the engine still running, your mower will shut off if you fail to set the parking brake first.   

Fix: Refer to your John Deere operating manual to ensure you are operating your lawn mower correctly, so you don’t set off the safety features that shut off your lawn mower.