7 John Deere L120 Problems and Easy Fixes

John Deere L120 Problems

If you love gardening and want to keep your garden in tip-top condition, John Deere has plenty of tractors for various grass-cutting tasks.

While most mowers will not cut grass longer than 4 inches, this John Deere model will rise up to the occasion. But just like any other mowing machine, the John Deere l120 has a fair share of issues.

Luckily, this post focuses on common John Deere L120 problems and their solutions. Read on to learn more;

7 John Deere L120 Problems

If you are the type of homeowner that intermittently cuts the lawn, the L120 mower could be the best option.

The tractor has a 42-inch deck with two rotary blades that can mow up between 1 and 4 inches of grass.

In addition, it features a lever that enables you to adjust the mowing height while seated. However, despite all these pluses, the tractor comes with the following issues:

  • Hydrostatic transmission problems
  • Smoke problem
  • Difficulties in starting the engine
  • Loss of energy while mowing
  • Hydro pump issue
  • Vibration problem
  • Grasscutting problems

Problem#1: John Deere L120 Hydrostatic Transmission Problems

Hydrostatic transmission plays an important role in running the wheels of a tractor.

It is a system that comprises mechanical components such as the drive axle, rubber, and metal horses via which the liquid is pushed.

Thus, the tractor slows down when the system develops issues and may crawl while mowing.

This may happen due to the hydro pump wearing out or when it cannot pump the right amount of oil. It could also happen when the hose is broken or the fuel filter is clogged.

The hydrostatic transmission system transfers power to the wheels from the engine via the hydraulic pumps.

But sometimes transmission could start slipping while the tractor is moving. As a result, the hydraulic starts to make noise as it tries to produce the pressure it needs to move the wheel.

The pump may be filled with air, so the pressure it creates may be insufficient to power wheels and enable it to ride small hills.

Solutions for l120 John Deere transmission problems

  • Purging the hydraulic drive system – it removes air to solve the problem.
  • Top up the engine oil if the level is too low.
  • Inspect the hoses and repair the damages.
  • Use a rag or a brush to clean the cooling fins.
  • The sluggish operation may be caused by overuse of fluids, so you may need to change the steering and hydraulic fluids.
  • Check the level of oil and the transaxle. If the oil level is low, top it up. You may also need to remove the transaxle and drain the oil through the plug vent.
  • Check the driving belts and the slipping belt.
  • If there is a hydraulic leakage, ensure to fix it.

Read: John Deere 3025e Issues

Problem #2: John Deere L120 Smoke Problem

When you notice smoke appearing from the side of the motor, it tells you that a problem needs to be fixed.

If you don’t take corrective measures, the engine overheats and gets damaged. The smoke could be due to engine blockage and a clogged crankcase vent.


  • Turn off the engine as soon as you notice smoke emanating from the covered part of the engine.
  • Clean the crankcase breather.
  • Inspect and adjust valve clearance.
  • Replace the gaskets and push rod.

Problem #3: John Deere L120 Loss of Energy While Mowing

There are cases where the tractor loses energy after a few hours of running. It may lose both speed and mowing power.

One of the causes of the problem is the height of the mower deck. This could happen when cutting taller dense grass.


  • Do not work on long wet grass.
  • Clear the deck and sharpen the blades.
  • Lift the deck to an appropriate height.
  • Ensure proper maintenance of the mower to prevent the reoccurrence of the problem.

Related: Troubleshooting ohn Deere La145 Problems

Problem #4: John Deere L120 Difficulties In Starting The Engine

Starting issues are common in almost all john deere lawn-mowing tractors, such as the La145 and L130 models. So when your John Deere L120 refuses to start, don’t panic. It could be caused by any of the following issues:

Low fuel – when the fuel level drops below a certain level, the mower may not start. This could happen if the mower has stayed inactive for over 30 days.

Faulty battery – if the mower clicks when you start it, the battery could be faulty. In this case, you must use a multimeter to test the voltage. If it is less than 12.7 volts, the tractor will not start.

Dirty fuel filter– the filter keeps dirt out of the carburetor. So after days of mowing and cutting grass, the fuel lines could get blocked.

Thus, you may need to clean the fuel tank or replace the fuel line and filters. Faulty Spark Plug – the plugs need to be changed every 100 hours of service.

But sometimes, you may forget to change them. So the tractor will remind you by refusing to start.


  • If the fuel level is low, refuel the tank.
  • If the voltage is down, recharge the battery.
  • Replace the fuel filters.
  • Change the faulty spark plug.

Problem #5: John Deere L120 Hydro Pump Issue

When you discover that riding the mower starts fast but slows down after some time, the fuel pump could have an issue, or the deck could be lodged.

If it experiences a problem when you are not cutting grass, it could be a pump issue. Typically, the hydro pump wears out with time.

So after some time, it starts getting hot due to wearing out. The pump may no longer pump the oil as it should.

Instead, it will start to produce strange sounds as it tries to pump the oil. In such a case, the pump may not produce the pressure required to move the mower.


  • If the hydro pump fails, the mower’s lifespan is shortened, so the remedy to the problem lies in regular checking and monitoring of hoses, oil levels, and connectors.
  • Monitoring may help you identify and fix issues before they worsen.

Recommended reading: Most Common John Deere 757 Issues

Problem #6: John Deere L120 Vibration Problem

When you turn on the engine, you may hear intolerable vibration, indicating that the blades are not properly aligned. The vibration is annoying and could loosen the belt.

The possible cause of such vibration are debris in the mower deck.  So if the problem is not sorted out, the vibration could become intensive and make it difficult for you to work.

The vibration becomes intensive when the sheaves are displaced from their position.


  • A thorough engine inspection may be necessary to ascertain the condition. If it is in bad condition, you may need to replace it.
  • Check if there is debris on the mower. If there are, they must be removed. Similarly, if the blades are bent or imbalanced, they may cause vibration. So the best thing to do is to remove them before they lead to the problem.

Problem #7: John Deere L120 Grass Cutting Problems

When you notice that the machine is not cutting grass evenly when moving too fast, the mower decks may be having issues.

Similarly, when you discover that the mower cuts the grass too short but exposes the roots, the deck could have some issues.

The tractor could be imbalanced because the tires are not inflated. If you continue cutting the lawn, it may appear ragged and uneven.


  • Find out if the tires are well inflated; if not, inflate them according to the psi number indicated on each tire. Inflating the tires enhances the balance and makes the mower cut the grass evenly.
  • Adjust the deck by raising the side until the John Deere l120 rear end of the deck are at the same level. Measure the height from the front and the center of the deck and adjust accordingly.

See: Common John Deere L130 Mower Problems

John Deere l-120 troubleshooting

Hydrostatic transmission problems– Worn-out hydro pump
– Broken hose
– Clogged fuel filter
– Purge the hydraulic drive system
– Top up engine oil
– Inspect and repair hoses
– Clean cooling fins
– Change steering and hydraulic fluids
– Check and adjust driving belts
– Fix hydraulic leakage
Smoke problem– Engine blockage
– Clogged crankcase vent
– Turn off the engine
– Clean the crankcase breather
– Inspect and adjust valve clearance
– Replace gaskets and push rod
Loss of energy while mowing– Improper mower deck height
– Cutting dense grass
– Avoid long wet grass
– Clear the deck and sharpen blades
– Lift the deck to appropriate height
– Properly maintain the mower
Difficulties in starting the engine– Low fuel level
– Faulty battery
– Dirty fuel filter
– Faulty spark plug
– Refuel the tank if fuel level is low
– Recharge the battery if voltage is low
– Replace fuel filters
– Change the faulty spark plug
Hydro pump issue– Worn-out hydro pump– Regularly check and monitor hoses, oil levels, and connectors
Vibration problem– Improper alignment of blades
– Debris in the mower deck
– Thoroughly inspect the engine and replace if necessary
– Remove debris from the mower deck
– Check and balance blades to avoid vibration
Grass cutting problems– Unbalanced tires
– Deck alignment issues
– Ensure tires are properly inflated to the recommended PSI
– Adjust the lawn mower deck to ensure the rear sides are at the same level
– Measure and adjust the deck height from the front and center to achieve even cutting

John Deere l120 review

The l120 John Deere tractor is a reliable and well-built machine. It offers solid cutting performance and comfortable operation.

Its sturdy construction ensures durability. The wide cutting deck efficiently covers larger areas. The mower’s sharp blades deliver a clean and even cut, resulting in a professional-looking lawn.

The L120 also offers versatility with optional attachments for various lawn care tasks. However, potential drawbacks include a slower speed, limited turning radius, maintenance requirements, and a higher price tag.

Overall, the L120 is a satisfactory choice for homeowners. However, it is important to consider individual needs and preferences before making a purchase.

You may also want to learn more about the John Deere 2305 Problems and solutions.


Is John Deere L120 a good mower?

John Deere l120 features a 20 HP engine that gives it the power to cut anything. But to get the best service, you must consistently check and replace spark plugs, fuel pumps, and air filters. 

Thus, if you are good at DIY tasks, the tractor could be a good choice. Moreover, the machine could be the best option if you want something you can rely on to tame unruly grass.

Interesting Read: John Deere S120 Vs S130

What are the most common John Deere L120 issues?

The most common l120 issues include vibration, engine starting problems, or losing power while mowing. 

Also, the machine experiences smoke problems, especially if it is not serviced regularly and may develop hydro pump issues.

What engine does John Deere l120 have?

The mower is fitted with Briggs & Stratton CV40 with a 655cc 40ci displacement engine. The engine allows you to set a mowing speed you can control, enabling you to pay attention to how it mows the grass. 

Also, the tractor features an automatic transmission system that allows you to drive smoothly without needing to shift gears manually.

How should one store John Deere tractor?

When the mower is not in use, you could store it in the garage until needed. Unfortunately, the machine runs on gasoline which contains ethanol that breaks down into loose deposits. 

These particles could be deposited in the engine. So ensure to empty all the fuel before storing it and fill it with fresh fuel when you want to use it.

See: John Deere Z930M Issues

John Deere l120 problems summary

John Deere l120 is a powerful mower you may need to consider if looking forward to neatly cut grass. The tractor is 38.6 inches tall, 36 inches wide, and 69 inches long.

Despite several John Deere L120 problems, it can move forward at 5.2 mph and reverse at 2.9 mph.

In addition, it could hold about 2.1 gallons of gasoline, thus allowing you to go about your grass-cutting tasks without worrying about fuel.