John Deere S120 Problems

The John Deere S120 lawn tractor, while a popular choice for homeowners seeking a reliable machine for maintaining their yards, isn't without its potential pitfalls. Like any mechanical device, the S120 can experience issues ranging from minor annoyances to more significant problems that require troubleshooting and repair. Understanding these common issues and how to address them can save you time, money, and frustration, ensuring your lawn stays beautifully manicured.

Starting Troubles: Why Won't My S120 Fire Up?

One of the most frequently encountered problems with the John Deere S120 is difficulty starting. This can manifest in several ways, from a complete failure to crank to a sluggish start that eventually gets the engine running. Let's break down the potential culprits.

Dead Battery: This is the most common culprit. A weak or dead battery simply doesn't have enough juice to turn the engine over. Check the battery voltage with a multimeter. Ideally, it should read around 12.6 volts when fully charged. If it's significantly lower, try charging the battery. If it still won't hold a charge, it's time for a replacement.
Loose or Corroded Battery Connections: Even if the battery is good, loose or corroded connections can prevent the flow of electricity. Inspect the battery terminals and cable ends. Clean any corrosion with a wire brush and ensure the connections are tight. A dab of dielectric grease can help prevent future corrosion.
Faulty Starter Solenoid: The starter solenoid is a small electrical switch that relays power from the battery to the starter motor. If it fails, the starter motor won't engage. You can test the solenoid by using a multimeter to check for voltage at the starter motor when the key is turned to the start position. If there's no voltage, the solenoid is likely the problem.
Defective Starter Motor: The starter motor is responsible for turning the engine over. If it's faulty, it may not engage or may turn over very slowly. A mechanic can test the starter motor, or you can try tapping it with a hammer while someone tries to start the engine. If it starts after tapping, the starter motor is likely failing.
Safety Interlock Switches: The S120 has several safety interlock switches designed to prevent accidental starting. These switches are located on the seat, brake pedal, and cutting deck. If any of these switches are faulty, the engine won't start. Make sure the seat is properly engaged, the brake pedal is fully depressed, and the cutting deck is disengaged. You can test the switches with a multimeter to check for continuity.
Fuel Issues: A lack of fuel can also prevent the engine from starting. Check the fuel level in the tank. If the tank is empty, add fuel. Also, check the fuel filter for clogs. A clogged fuel filter can restrict fuel flow to the engine. Replace the fuel filter if it's dirty.

Uneven Cutting: Why Is My Lawn Looking Patchy?

An uneven cut is another common complaint among John Deere S120 owners. This can be caused by several factors related to the mower deck and blades.

Dull or Damaged Blades: Dull or damaged blades are the most common cause of an uneven cut. Dull blades tear the grass instead of cutting it cleanly, resulting in a ragged and uneven appearance. Sharpen your blades regularly, or replace them if they are damaged. Sharpening blades every 25 hours of use is a good rule of thumb.
Uneven Tire Pressure: If the tires are not inflated to the correct pressure, the mower deck will not be level, resulting in an uneven cut. Check the tire pressure with a tire gauge and inflate them to the recommended pressure.
Bent or Damaged Mower Deck: A bent or damaged mower deck can also cause an uneven cut. Inspect the mower deck for any signs of damage. If the deck is bent, it may need to be repaired or replaced.
Incorrect Mower Deck Leveling: The mower deck must be properly leveled to ensure an even cut. Refer to your owner's manual for instructions on how to level the mower deck. This is a crucial step that many owners overlook.
Clogged Mower Deck: Grass clippings and debris can build up under the mower deck, causing an uneven cut. Clean the mower deck regularly to prevent buildup.

Engine Problems: When Things Get Noisy and Smoky

Engine problems can range from minor annoyances to serious issues that require professional repair. Here are some common engine problems with the John Deere S120:

Engine Overheating: Overheating can be caused by a variety of factors, including a clogged air filter, a low coolant level, or a faulty water pump. Check the air filter and clean or replace it if it's dirty. Check the coolant level and add coolant if necessary. If the engine continues to overheat, you may need to have the water pump inspected.
Engine Knocking: Engine knocking is a sign of a serious problem. It can be caused by low oil pressure, worn bearings, or detonation. If you hear engine knocking, stop using the mower immediately and have it inspected by a mechanic.
Excessive Smoke: Excessive smoke can be a sign of several problems, including burning oil, a faulty carburetor, or a blown head gasket. The color of the smoke can provide clues about the cause of the problem. Blue smoke indicates burning oil, black smoke indicates a rich fuel mixture, and white smoke indicates burning coolant.
Loss of Power: A loss of power can be caused by a variety of factors, including a clogged air filter, a clogged fuel filter, or a faulty spark plug. Check the air filter and fuel filter and clean or replace them if they're dirty. Replace the spark plug if it's worn or fouled.
Carburetor Issues: Carburetor problems can lead to a variety of engine issues, including rough running, stalling, and difficulty starting. The carburetor may need to be cleaned or rebuilt.

Transmission Troubles: Slipping and Jerking

The John Deere S120 features a hydrostatic transmission, which provides smooth and variable speed control. However, like any transmission, it can experience problems.

Slipping Transmission: A slipping transmission is a sign that the transmission is not properly engaging. This can be caused by low transmission fluid, worn transmission parts, or a faulty transmission pump. Check the transmission fluid level and add fluid if necessary. If the problem persists, you may need to have the transmission inspected by a mechanic.
Jerking Transmission: A jerking transmission can be caused by air in the transmission lines, a faulty transmission pump, or worn transmission parts. Bleed the air from the transmission lines. If the problem persists, you may need to have the transmission inspected by a mechanic.
Loss of Drive: A complete loss of drive can be caused by a broken drive belt, a faulty transmission pump, or a damaged transmission. Inspect the drive belt and replace it if it's broken. If the drive belt is intact, you may need to have the transmission inspected by a mechanic.

Steering Problems: Wandering and Hard to Turn

Steering problems can make it difficult to control the mower and can be a safety hazard.

Wandering Steering: Wandering steering can be caused by loose steering components, worn tires, or incorrect tire pressure. Check the steering components for looseness and tighten them as necessary. Check the tire pressure and inflate them to the recommended pressure.
Hard to Turn Steering: Hard to turn steering can be caused by low tire pressure, a lack of lubrication in the steering components, or a faulty steering gear. Check the tire pressure and inflate them to the recommended pressure. Lubricate the steering components with grease. If the problem persists, you may need to have the steering gear inspected.

Electrical Gremlins: Lights and Fuses

Electrical problems can be frustrating and can prevent the mower from starting or operating properly.

Blown Fuses: Blown fuses are often a sign of an electrical short. Identify the cause of the short and repair it before replacing the fuse.
Faulty Lights: Faulty lights can be caused by a blown bulb, a loose connection, or a faulty switch. Check the bulb and replace it if it's blown. Check the connections and tighten them as necessary.
Wiring Issues: Damaged or corroded wiring can cause a variety of electrical problems. Inspect the wiring for damage and repair or replace it as necessary.

Preventing Problems: A Little Maintenance Goes a Long Way

Regular maintenance is the key to preventing problems with your John Deere S120.

Regular Oil Changes: Change the engine oil and filter regularly, as recommended in your owner's manual.
Clean Air Filter: Clean the air filter regularly to prevent dust and debris from entering the engine.
Sharpen Blades: Sharpen the mower blades regularly to ensure a clean and even cut.
Check Tire Pressure: Check the tire pressure regularly and inflate them to the recommended pressure.
Lubricate Moving Parts: Lubricate the moving parts of the mower regularly with grease.
Store Properly: Store the mower properly during the off-season to prevent damage.

Frequently Asked Questions

Why won't my John Deere S120 start? A dead battery, loose connections, or a faulty safety switch are common culprits. Check these components first.
How often should I sharpen my mower blades? Sharpen your blades every 25 hours of use, or more frequently if you mow in sandy or abrasive conditions.
What type of oil should I use in my S120? Consult your owner's manual for the recommended oil type and viscosity.
How do I level the mower deck on my S120? Refer to your owner's manual for detailed instructions on leveling the mower deck.
Where can I find replacement parts for my S120? You can purchase replacement parts from your local John Deere dealer or online retailers.

In Conclusion

While the John Deere S120 is a capable lawn tractor, understanding its common problems and how to address them is crucial for maintaining its performance and longevity. Performing regular maintenance and addressing issues promptly can prevent costly repairs and ensure your lawn stays looking its best.