Every time my mower shuts off when it’s not supposed to, I shake my head in frustration. The issues with stalling mowers could come from so many different places that it can be annoying to sort out. Electrical systems, belts, wires, and various shorts can all cause your mower blades to stall.
One way to help rule out what exactly is causing your garden equipment to die unexpectedly is to pay attention to when the mower dies. If the engine stalls when I put the mower in gear, I have a better idea of where to check, like the seat safety switch. If it happens right after the engine engages, on the other hand, it could be a battery issue or be in need of a carburetor repair. Read on to discover the reasons your mower model shuts off and how to solve this common issue.
What Causes Lawnmowers to Shut Off?
Figuring out why your riding mower or self-propelling walk-behind mower is dying when put into gear can take a bit of patience and a fair amount of mechanical know-how. If you are lucky, a thorough cleaning may be all it takes to get your mower working perfectly again. Sometimes it takes a bit more work than that. Below is a quick guide to some of the common issues with starting lawnmowers.
| Components | Issues | Quick Fix |
| Battery | Shorts, not enough juice, and bad batteries | Clean terminals, charge or replace the battery |
| Wires | Shorts, pinch, loose connection | Inspect tension points in circuitry and repair or replace wiring as needed |
| Speed Module | Loose connections and module failures | Secure wires and housings to avoid abrupt stalls or replace mower deck drive pulleys |
| Belts | Wrong sized or old mower drive deck belt needs a replacement | Replace the belt and any other damaged components near the mower deck drive belt |
| Engine | Dirty or faulty engine parts and intake air issues | Keep the mower clean, including the engine and ensure safety measures on the engine models are not malfunctioning |
| Blades and Mower Gear | Damaged or dull blades and faulty clutch pedal or electric clutch connection | Replace damaged mechanical and electrical pieces and test all systems before starting |
| Valves and Lines | Dirty or broken lines and valves, as well as bad fuel or diluted fuel | Clean and replace any broken valves, siphon bad fluids and replace with new correct fuels and lubricants |
| Safety Switches | Faulty connections, wire shorts, and dirt in the seat switch junction | Clean switch housing and sensors, replace bad switches or repair loose and damaged connections where possible |
Battery
Without a maintained and amply charged battery, it is hard to start your lawn mower. If the mower is able to start, it may not have the juice to make it very far, and when the gears are engaged, the engine may cut off. If the problem is the battery, then there are quite a few things you can do before you need to completely replace the power source.
The first thing you should do is clean any corrosion from the terminals and any residue near the connections. Once the area around the battery is clean, you can inspect that there is no damage to the battery box. If the engine still doesn’t respond correctly, you can attempt to use an external charger to top off the battery. If this still isn’t sufficient, you will need to replace the battery or continue troubleshooting the gear shut-off issues.
Wires
Between the time the engine turns over and when the mower is put into gear, a lot of electrical signals and mechanical responses occur in the wiring woven throughout the mower assembly. If any of these connections are unable to be completed, the mower will shut off, and you will not shift into gear successfully. Due to the sheer number of connections that need to be tested, it can be time-consuming to fix a wiring issue that is not easily identifiable.
The best way to inspect wiring is to work backward from the most likely wiring issue to the least likely and hope you hit correctly early on. Checking wires can be done visually, but if no damage is identified, you will want to use a voltage tester to see if any black wires are dead that shouldn’t be. Test electrical connections at junction boxes, not at the actual electrical component, to avoid damaging expensive electrical parts.
Speed Module
Riding mowers and self-propelled garden tools have a lot of horsepower to drive powerful blades and operate PTO equipment. That HP doesn’t translate to speed in forward motion keeping you safe with a governor or speed-advanced module, which ensures your mower moves at a slow speed ideal for cutting turf. Module failure of this key feature can cause a mower to die when put into gear.
In much the same way as low battery voltage, a malfunction speed module will let the engine begin but act up when the mower is put into gear. Sometimes it can also happen when switching to a higher gear or engaging the mower blades. Whenever it occurs, checking this component can help with mower reliability issues.
Belts
Drive belts in the garden tractor engage the forward movement of the machine and can cause problems when put into gear. If the belt is not connecting properly, then there is a real chance the engine will stall and the mower will shut off. To avoid this, always check belts when doing routine maintenance.
Drive belts wear down over time, and occasionally an incorrect belt can be installed, leading to drive engagement issues. In higher gears or at higher RPMs, the drive belt may slip and kill the engine immediately. This issue is usually easy to identify as you will not be able to continue until it is replaced or repaired.
Engine
Engine issues can be numerous and can stop your mower when the gears are engaged. Each stage of ignition has the potential to stall if there are engine problems. If there are problems with lubrication, air intake, or engine firing, then you can check the motor area and connections first.
If your engine has the power to start but cannot stay on when put into gear, then you should go through a quick troubleshooting process. Cleaning and replacing filters and fluid, and electrical conduits can give you a better idea of what is going wrong. Replacing spark plugs and other mechanical parts can ensure smooth operation and ease of gear changing in future mowing sessions.
Blades and Mower Gear
Dull, damaged, or restricted blades, as well as faulty or fritzy gear or mechanical mower parts, can stop your mower short. If your gear load seems too heavy for what you are trying to do in the yard, it can be a blade issue, and seizing cutting parts will kill the motor to protect the mower’s systems. If changing gears results in a sudden cut, then it could have to do with the gear change and clutch system.
Replacing damaged blades or sharpening dull blades can keep your mower strong enough to cut through thick turf and prevent turning off abruptly. If the blades are fine, you will want to make sure that none of the clutch or gear mechanical parts are damaged. If the mechanical pieces are operating correctly, then check the clutch electrical systems for shorts or a faulty clutch switch.
Valves and Lines
The tubes by which fuel and lubrications circulate through the engine and mower need to be maintained and inspected whenever mower troubles arise. Since the fuel and lubrication mostly take place in the engine area, it is a good idea to start your inspection there. Replace any damaged valves or lines that are obviously leaking fluid.
If the lines and valves are intact, you can examine the fluid to make sure it isn’t expired, especially in the fuel lines. Check that the flow of fuel is not impeded and that the fuel shutoff valve is open. If you will be storing a mower for several months with fuel inside, add extra fuel to top off the tank and mix in a fuel stabilizer.
Safety Switch
Riding mowers can be dangerous machines and come with a myriad of safety switches to help make sure operators, and those nearby are not at risk during normal operation. When there is a faulty safety switch, instead of making the mower more dangerous by not doing the job it was intended for, the mower will simply cut out until the problem is fixed. Finding the bad safety switch can be tough, however.
A mower will often have a PTO switch, key switch, brake switch, reverse switch, neutral switch, ignition switch, drive switch, lever switch, parking brake safety switch, grass box safety switch, and a seat safety switch. When it comes to mowers cutting off when put in gear, the most common culprit is a faulty seat switch. Even when you are in the seat ready to mow, the operator’s presence seat switch detects no rider and immediately kills the engine. Start your inspection there if your mower dies in a similar way to that described above.
How to Fix Mower Engine Shutoff?
Fixing issues with your mower dying when it is put in gear takes a bit of trial and error and a lot of troubleshooting. Once you figure it out, you will need to replace or repair the affected components and ensure that your mower is safe and ready to operate. Below are the steps to take to do a full mower diagnostic and hopefully fix the issue with the mower shut off when put in gear.
Clean the Mower Deck
A clean mower is much easier to inspect and repair than one covered in lawn debris. Clean the outside of the body, engine components, and the mower deck and blades to give yourself a clear picture of faulty components. Park the mower on your lawn to perform cleaning and then move it to a solid surface for a mechanical and electrical inspection.
Remove Spark Plugs
If you will be working anywhere where an abrupt mower start-up will cause injury or death, remove the spark plugs before continuing. Taking out the spark plugs when you are not safely testing specific components that need ignition can keep you safe. Inspect spark plugs and clean terminals and replace worn-down and non-responsive plugs. Store good plugs in a cool-dry location where they will be good to go when you need them next.
Check Manual Parts
All of the mechanical components, like belts, pulleys, hardware, and fixtures, can be examined and tightened or adjusted. Making sure that all the parts that move are lubricated, and the parts that shouldn’t move are secured can go a long way in making sure your mower runs at its best. Any parts that are obviously damaged or worn down should be replaced before using the equipment again.
Test Electrical Systems
Using voltage and circuit testers, examine any problematic electrical areas that need to be repaired or replaced. Mowers move haphazardly on uneven lawns, and wires can be pinched, damaged, or slip out of connections. When this happens, a short will stop your mower dead and may even spark internally. After a short, entire junctions and components may no longer work and need to be replaced. Test electrical systems at junction boxes and not at the system component to avoid shorting out expensive parts.
Inspect and Replace Damaged Components
Throughout your inspection, replace anything that seems old, wrong, or broken. If you properly maintain your mower, it will run well for much longer. Some parts will break down over time and need to be replaced. Neglecting repair of these systems can result in worse damage and safety issues in your mower down the line.
Tune-Up and Maintenance
When everything is tightened, cleaned, and running, well, you can top off and replace filters and other changeable parts. Cleaning fuel tanks and adding high-quality fluids can give your mower an extra boost and reduce pollution while increasing performance. Tightening loose bolts and attachments can prevent internal damage and costly repairs.
Put Together and Start-Up
If everything is repaired, replaced, and properly maintained, then you can put the mower back together and do final testing. Engine parts should be tight, blades sharp and secure, and all mechanical and electrical systems tested and confirmed working. Now is the time to replace your spark plugs, hook up your battery and start everything up. When you put your mower in gear, it should roll smoothly onto your lawn and be ready for an enjoyable turf trimming session.