Lawn mower bad starter. How To Know If a Tractor Starter Is Bad – 6 Steps To Check

How To Know If a Tractor Starter Is Bad – 6 Steps To Check

When your tractor doesn’t start, one of the most common causes is that the starter or solenoid has gone bad. That’s not the only cause, though, so you need to find out for certain that the issue is the starter. How do you know if a tractor starter is bad?

Here’s how to know if a tractor starter is bad in 6 steps:

  • Try to start the engine.
  • Listen to the sound of the starter.
  • Check if there’s smoke coming from the engine.
  • Inspect the starter for gas or oil.
  • Test your lights.
  • Test the solenoid.

Like any vehicle with an engine, tractors have starters that function to spark the combustion within the engine and make it go. When that starter malfunctions for whatever reason, there are several telltale signs you can look for to pinpoint the starter as your issue. I’ll be going over the most common symptoms that signify a tractor starter has gone bad, including the few reasons why this happens.

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Try To Start the Engine

Having issues with starting the engine is the first sign that you have a starter problem. However, problems with the battery and alternator can also cause the tractor to not start, so this isn’t an immediate sign of a bad starter on its own.

When the tractor engine won’t start, you’ll hear a clicking noise when trying to start your tractor, but the engine will refuse to turn over and start. When combined with other signs listed below, you can tell if the starter is bad or not. If this isn’t accompanied by one or more other things listed, you may wish to look at your battery or alternator as the culprit.

Listen to the Sound of the Starter

Have someone else try to start the tractor as you listen carefully. Normally, when you turn the key, the starter engages and makes a loud clicking noise. If you don’t hear this happen when the key is turned, you may be looking at mechanical issues with the starter.

Lack of a clicking noise indicates a mechanical problem with the starter or a complete failure of the solenoid. Either there’s no power going to the starter solenoid at all because it’s bad, or the starter isn’t engaging the way it should.

Check if There’s Smoke Coming From the Engine

If you see smoke coming from the engine when it won’t start, you may be looking at a blown starter. The starter is a mechanical component powered by electricity, and electrical problems can make it stop working and emit smoke.

The fuse in the starter can blow, or shorts can occur within the starter’s wiring and start an electrical fire. Either of these is very bad and needs to be checked out by a qualified professional ASAP. Without immediate attention, electrical issues can spread and cause damage to other components within the tractor.

Inspect the Starter for Oil or Gas

Depending on the engine layout of your tractor, oil or gas from the fuel tank, gearbox, or other areas can leak and soak the starter. You can visually inspect the starter to see if it’s wet and smells like fuel or oil. If so, you’re looking at both a gas/oil leak and a bad starter. Start checking your gaskets immediately!

How to Diagnose, Test, and Replace Bad Starter Solenoid on Riding Lawn Mower

Oil or gas soaking a starter will drastically lower its lifespan, not to mention reduce its performance in the meantime. A brand-new starter that gets soaked in oil or gas can go bad in as little as six months.

When the solenoid gets wet it can’t produce the optimal amount of voltage, which manifests in trouble cranking the engine.

Test Your Lights

Another thing to look for after the engine doesn’t start is a lack of other electrical problems. Namely, check your lights. If the lights are working, that means your battery and alternator are fine, and that the issue is more likely the starter after all.

Test the Solenoid

When the starter solenoid fails, the starter won’t work at all, but the only way to be sure the solenoid is dead or bad is to test it.

To test the solenoid, you’ll need a test light and the location of your starter. In most engines, it’s a big cylinder with a smaller cylinder attached near the transmission and a wire coming to it from the battery.

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How To Test a Starter Solenoid With a Test Light:

  • Ground the black lead of the test light. You can do this by pressing it into any bare metal in the tractor engine or the black lead of the starter.
  • Once grounded, press the test light’s red lead into the starter’s positive terminal and make sure it’s making firm contact.
  • If you’ve attached the test light properly and the solenoid is working, the test light will light up. If not, it means the solenoid isn’t working and needs to be replaced.
  • If this terminal has power, it’s time to test the lower terminal. The lower terminal only has power when you’re trying to start your engine, so you’ll need someone to try and start the engine.
  • Ground the test light and connect the red lead to the lower terminal on the starter.
  • Have a friend or loved one try to start the tractor.
  • If the test light doesn’t light up this time, it means the solenoid isn’t transferring power to the starter and you have bad wiring within the starter.

If you need more guidance this YouTube video does an excellent job of laying out the testing process as well as outlining exactly how the solenoid works on a tractor:

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How to Test a Riding Lawn Mower Starter

Riding Lawn Mower Won’t Start No Clicking

It could be a variety of factors if your riding lawn mower does not start when you flip the key to start the engine. It can be anything from loose battery connections, fuses, the ignition switch, or something more serious.

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Luckily, if you end up saying my riding mower does nothing when I turn the key, you can go through some troubleshooting on your riding lawn mower before you need the help of a dealer.

In our guide, you can find out more about a John Deere or Husqvarna riding lawn mower won’t start any clicking or any other model you have. By the end, when you face not even a click, you’ll have enough information to run through the starting procedure to check all the items that could cause the issue.

Then, in the space of minutes, you could pinpoint the problem and get mowing your lawn without further issues. (Read Riding Lawn Mower Snow Blower Combo Guide)

How Do I Know If My Riding Lawn Mower Solenoid Is Bad?

What does it mean when you flip the key and hear a click? When you hear the click, the starter solenoid coil receives power from the battery via the ignition switch.

If you don’t hear that click, the starter solenoid is broken, or the starter solenoid coil isn’t receiving power.

We’ll teach you how to find the problem by inspecting the battery, solenoid posts and coil, fuse, ignition switch, brake interlock switch, and blade switch on your riding mower.

While lawnmowers are different, much of the troubleshooting techniques are the same. The fundamental distinction is that you may need to consult your model’s wiring diagram if you detect issues.

How the riding mower starting system operates:

It helps to know how the starting system works to narrow down the problem. Many issues look like problems when safety switches are engaged. Make sure no safety switch affects your troubleshooting.

  • The positive red battery connection connects to one of the starter solenoid terminal posts (positive).
  • The black wire that connects to the other major terminal on the starter solenoid (negative) provides power to the starter motor, which allows the engine to start.
  • A short red wire runs from the red solenoid terminal post to the ignition coil at the bottom of the starter solenoid, carrying power through the ignition switch.
  • The ignition switch provides power through the white wire to energize the coil within the solenoid when you turn the key to the start position.
  • The coil closes an internal contact, sending power from the red battery connection to the black wire, which turns the starter motor.

Do I have a dead battery?

A dead battery will prevent the solenoid coil from clicking since it will not power up the starter system.

  • Use a multimeter to measure the DC voltage across the battery terminals to inspect the battery.
  • Put on your safety goggles and work gloves.
  • Remove the key from the ignition.
  • Look at the battery. To access the battery on this style of riding lawn mower, you must elevate the seat.
  • Touch the red multimeter probe to the positive or red battery terminal and the black multimeter probe to the negative or black battery terminal with the multimeter set to measure DC voltage.
  • The battery should measure over 12 volts of DC if it is in excellent condition.
  • If it’s less than 12 volts, you have a weak or dead battery, and you’ve probably located the source of the problem. The starter solenoid coil will not power if the battery is weak or dead.
  • Using a charger, try recharging the battery. You can use jumper cables to jump-start a riding lawn mower with a 12-volt battery in a pinch.
  • Replace with a new battery if it won’t charge.

If the battery is weak or dead, you can find there isn’t enough power for the fuel pump. The fuel filter could also cause issues with lack of fuel. Checking or changing the air filter can also help while doing your troubleshooting.

A valve lash issue is much different. Fixing a valve lash problem is more intensive than checking the battery and terminal connections. (Read Troy Bilt Riding Mower Oil Type)

Check solenoid power

Power is delivered to the red battery cable if the battery works appropriately. Is voltage flowing to the red terminal post through the red battery cable? To verify this, take a voltage reading at the red terminal post.

  • Connect the multimeter’s red probe to the starter solenoid’s red post and the black probe to the battery’s negative terminal. It should measure more than 12 volts.
  • Check the battery terminals and cable leads for corrosion if the battery voltage is less than 12 volts. Use a wire brush to remove rust from the battery terminals and battery cable leads; corrosion can prohibit the red solenoid post from receiving power.
  • Recheck the voltage. Replace the red battery wire if it still doesn’t measure over 12 volts at the red post.

Check solenoid coil power

Now you’ve established the red terminal is receiving power, you need to determine if the solenoid coil is receiving power when you turn the key on your lawn tractor. Or, you have a faulty solenoid, leaving you with a tractor won t start, no click.

The starter solenoid is to blame if the voltage is measured at the coil, but the internal contact does not click. However, it clicks when the solenoid gives power to the starter motor.

  • Unless you have a helper to turn the ignition key while holding the solenoid coil wires probes, you’ll need clip-on meter probes. Remove the white and black wires from the solenoid’s spades.
  • Set the multimeter to DC voltage measurement.
  • Connect the white wire female spade connector to the red meter probe and the black wire female spade connector to the black wire female spade connector.
  • Turn the ignition key to the start position, then note the voltage reading on the meter display before turning it off.

If the battery voltage is measured with a multi-meter, it will be greater than 12 volts. The starter solenoid should be replaced if the coil receives power but does not close the internal contact to the starter motor.

There is a break in the circuit to the solenoid coil if it reads 0 volts. The starter solenoid is most likely fine; it simply lacks power. It’s time to test the coil circuit. (Read Riding Lawn Mower Won’t Stay Running – What To Do)

Test lawnmower coil circuit

First, we’ll test the circuit’s ground. The black wire links the solenoid coil to the metal frame of the riding mower. A wire break prevents power to the coil.

  • Using a meter, we check for resistance between the black wire’s female spade and the metal frame of the mower and ground wire.
  • Before testing resistance, disconnect the negative battery cable and positive battery cable from the mower.
  • Keep the cables away from the battery terminals so they don’t accidentally restore power to the posts.
  • Set the multimeter to measure resistance and ground it by touching one probe to the black wire female spade and the other to the bare metal on the mower frame.

Resistance around 0 ohms suggests the black wire is grounded. Infinite resistance shows a break in the black ground wiring. The engine should start after the black wire has a good path to the ground.

Check Fuses

Next, you’ll need to check the hot side of the circuit, which starts with the small red wire on the starter solenoid terminal and finishes with the white wire that connects to the coil spade, if the ground side is alright.

A fuse, the ignition switch, the brake switch, and the blade switch are all part of the circuit.

  • Start with the simplest and check for a blown fuse, which you can tell by glancing at it.
  • The fuse on this mower is immediately next to the starter solenoid, but we have to remove the battery and battery box to get to it.
  • Pull the fuse from the holder using the zip tie.
  • If you’re not sure if the fuse is blown, use your multi-meter to check for continuity through the fuse.
  • Remember, if the fuse blew because of a component or wiring fault. You’ll need to figure out what’s causing a blown fuse and how to fix it.
  • Reinstall the fuse in the holder and secure it with the zip tie.

A blown fuse or broken connection will measure infinite resistance. Infinite resistance means you’ll need to replace the parts. (Read Poulan Pro Riding Lawn Mowers Reviews)

How Do I Know If My Lawn Mower Ignition Switch Is Bad?

On your lawn tractor, many areas can cause issues with starting. Here’s a quick rundown of what you would check first.

Battery Charge?

Check battery voltage, 12.65v is fully charged, 12.05v is half-charged, and needs recharging.

Low voltage shows a defective battery that may not recharge. A battery must be charged to be tested; hence a battery charger is required. The mower’s alternator will eventually charge the battery if it isn’t malfunctioning. You can try the crank test once the battery is fully charged (about 70%).

If the lights don’t function, use a voltmeter to test the battery’s charge, or you could have a blown fuse.

Jumper Cables

If you don’t have a charger, a set of jumper wires, a car, or any 12volt battery will do.

Check Safety Sensors

Riding mowers are fitted with safety measures to prevent operator error or accident. Sensors/switches regulate safety features on mowers, which are usually wired into a control module. One of the more common is the weight sensor in the seat, so the starting procedure can’t finish unless you are sitting on your mower. (Read Bluegrass Vs Tall Fescue)

Check Control Module

Modern mowers contain control modules, printed circuit boards comprising relays and resistors.

Assuming all sensors are engaged, the control module starts the starter when the ignition switch is turned on.

Visually inspect these modules for loose connections or water damage, as each module comes with an internal or external fuse. For example, a mower’s primary fuse might blow, cutting off power to the ignition system.

Check Ignition Switch

Improperly connected ignition switches can cause a host of issues with the ignition system. Ignition switches can convey commands to the control module.

If your mower lacks a control module, the safety sensors are directly connected to the ignition switch, leaving it open.

Common Problems

  • Problems with ignition switches include loose wiring, rusted or damaged terminals, and spinning ignition switches.
  • If you have the blade knob set to the on position, your engine won’t start. So make sure your ride-on mower is in the park and the knob set to off.
  • Remember, you’ll need someone to sit on the mower seat as you check the connectivity of the ignition wires and connectors.

When I Turn The Key On My Mower Nothing Happens?

Test Ignition Switch

Check continuity through the red wire from the starter solenoid post to the ignition switch.

  • Assemble a test set up for the red starter solenoid wire and the ignition switch
  • Open the mower hood.
  • Remove the ignition switch wire harness.
  • Pull the ignition switch out of the dash by the locking tabs.
  • Push the wire harness plug through the hole to test the contacts.
  • Place one probe on the starter solenoid post with the red wire and the other on the female plug spade with the red wire.
  • This section of wiring should have near 0 ohms’ resistance. Find and repair the red wire’s break if you get infinite resistance.

Test Brake Interlock Switch

We’ve isolated the circuit break to the part of the white wire that includes the brake switch and blade switch if the ignition switch is working. (Learn How To Cut Grass With Riding Mower)

Brake Switch

  • Remove the air duct mounting screws and pull out the brake switch.
  • Remove the fuel tank with care. If the tank is weighty, drain some fuel.
  • Remove the lower dash fastener and take it off. Now you may try the brake switch.
  • Note the white wires’ prongs, as these are the ones you’ll need to test the brake switch’s resistance.
  • Pull the wire harness off the brake switch.
  • Touch one probe to one prong and the other to the other prong that connects to the white wires.
  • If the brake switch works properly, it should measure near 0 ohms.
  • If you have infinite resistance, the brake pedal switch is broken.

Blade Switch

You must disassemble the clutch lever assembly to reach the blade switch.

  • Note the white wires’ prongs and remove the wire harness from the blade switch.
  • Set your multimeter to examine resistance and touch the probes to the white wire’s prongs.
  • The multi-meter should read near 0 ohms if the blade switch is working. If it reads infinite resistance, replace the blade switch.
  • If the blade switch works, a break in the white wire between the ignition switch and the solenoid coil prevents the coil from receiving power. Locate and fix the wiring fault.

After reading our troubleshooting tips, you should be able to start your mower.

How Do You Test A Starter Solenoid On A Riding Lawn Mower?

Riding lawn mowers come with many safety features and safety switches to stop the engine from starting unless certain conditions are met.

  • Parking Brake: Ensure the parking brake is engaged. This safety switch can be part of the brake pedal.
  • Blade Control: The blade control handle must be in the OFF position.
  • Seat cutout: Most riding mowers have a seat safety switch.

Wiring and Connections

The starter motor requires a solid battery connection like any other internal combustion engine.

  • Inspect the starter, solenoid, ignition switch, and battery connections. Remove corrosion with a wire brush and tighten all connections.
  • Check the grounding points. Grease or use liquid electrical tape for all connections.
  • Verify the starter motor bolts. Otherwise, the starter may move and not engage.

Bad Starter Solenoid

If you have a decent battery, but the riding mower won’t start when you turn the key on your riding mower, your solenoid may be broken and won’t pass any current through the ignition wiring to the spark plug.

The solenoid is simple to check with a 12V battery and a multi-meter

  • Unscrew the solenoid from the riding mower
  • Most solenoids have four posts: two for operation and two for battery connection.
  • Connect your multi-meter to the two large battery posts to test continuity.
  • Connect the battery’s negative to a spade terminal.
  • Connect the battery’s positive terminal to the other spade terminal:
  • The solenoid should click as it works.
  • Continuity/short circuit should show on your multi-meter.

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Riding Lawn Mower Won’t Start, No Clicking — Solutions When Your Riding Mower Does Nothing When You Turn The Key

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Dealing with a non-starting riding mower can be incredibly frustrating. However, if you’re experiencing a situation where the engine doesn’t make any clicking sounds, there may still be hope for a simple fix without having to replace the mower just yet.

Below, our experts have put together the potential issues with a riding mower that won’t start or click and provide troubleshooting tips to help your riding mower work again.

How to Fix a Riding Lawn Mower That Won’t Start

“Should I call a professional when the riding mower does nothing when I turn the key?” The answer is: not always. You should be able to find out the problem with your tractor or mower yourself. But first, ensure you set the parking brakes.

Then check if the blade is still disengaged. Your riding mower won’t work otherwise.

Materials You Will Need

  • Work gloves
  • Safety goggles
  • Multi-meter
  • Screwdriver
  • Wire brush

How a Riding Lawn Mower is Powered

Riding mower is powered by a four-cycle engine (intake, compression, combustion, and exhaust). Some mowers use gasoline as their fuel and a spark plug to combust it. Others are powered by diesel and require no spark plug. In either case, the engine runs the transmission and drive wheels, and rotates the cutting blades underneath the machine.

Like automobile car, riding mower requires to charge a battery, starter motor, and ignition switch. When you turn the ignition switch to the ‘Start’ position, 12 volt of direct current travels from the battery through the starter solenoid to the starter motor. This current also flows through a cable to the anti-afterfire solenoid in the engine

When you release the key to the ‘Run’ position, this DC of twelve (12) volts is then redirected. Instead of going to the starter and motor, it moves to the alternator and anti-afterfire solenoid only. Together, these parts help to charge the battery and start auxiliary power sources like headlights and power plugs.

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If your high-quality zero turn mowers work fine, you would hear a clicking sound between the ‘Run’ and ‘Start’ positions. This implies that the starter solenoid is getting power from the battery. On the other hand, when you don’t hear a click from the engine, the starter has failed, or its coil isn’t getting power from the battery.

Although mowers differ from models, they all work on the same principles.

Check and Charge/Replace Dead Battery

Battery troubles are one of the most common reasons a mower won’t run or click. A corroded battery won’t start an engine, and neither will a drained battery, when you forget to turn off the safety switch. Corrosion can be a usual problem for used riding lawn mower models at cheap of 500 below, so make sure to check this when you buy one.

A service monitor on a mower can help you identify when you’ve got battery troubles. But without one, you can check the battery using a multi-meter by following these steps:

  • Turn off the ignition system before accessing the battery.
  • Set the multimeter to DC voltage
  • Use the multi-meter’s red probe to touch the positive terminal and the black probe on the negative terminal.
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If the multitester reads more than twelve (12) volts, the battery is good. Otherwise, it is weak, or dead and you’ve found the problem with your mower.

  • Accessing the battery, which is usually under the driver’s seat.
  • Connecting the charger clips to the battery terminals.
  • Plugging the charger to a power outlet. The charger should work on at least 10volts to charge the battery. Still, a 12-volt charger is sometimes preferred.
  • Disconnecting the charger reversing the steps above.
  • Plugging the charger to a power outlet. The charger should work on at least 10volts to charge the battery. Still, a 12-volt charger is sometimes preferred.
  • Replacing the seat and reconnecting the new battery in your mower correctly.

If a simple recharge doesn’t work, you need to replace the battery pack in the mower. Avoid a jump start mower to prevent damages to the on-board system

Check the Ignition Switch

The problem with your mower could be with the switches. When you start the engine and your riding mower does not forward nor reverse, your ignition switch’s contacts complete a circuit. This circuit is from a red to a white wire, which is on the B-terminal and S-terminal, respectively.

  • Pull up the mower’s hood to access the ignition switch.
  • Remove its cable harness.
  • Remove the tabs to pull the ignition switch out of its slot.
  • Turn the key to the start position and set the multi-meter to measure resistance, not voltage.
  • Connect the black multi-meter probe to the B prong and the other to the S prong. These terminals are along each other’s diagonal at the bottom of the switch.
  • Use the key to turn the ignition switch and start the engine. The resistance should display on the multi-meter when you do this.

The top-rated riding mowers should have good ignition switch measuring 0 ohms. This means its contacts complete the B and S terminal circuit and can send voltage to the solenoid. On the other hand, a damaged ignition switch will measure infinite resistance.

Other common issues you can experience with a damaged ignition switch include loose wiring and connections, corrosion, or spinning ignition. To fix this problem, check the ignition wiring for corroded, damaged, or loose wires

Inspect the Control Module

A control module is a printed circuit with resistors, relays, and a ground side that receive commands from the safety switches. If the sensors in the motor work correctly, a circuit module will also output a command to the starter through the solenoid. However, not every mower has one.

Depending on your model, a control module could be anywhere, even under the seat. And if you notice that your high-quality electric riding mower won’t start and no clicking comes from the device, or cranking doesn’t work, then this module could be faulty.

There are two ways to check the control module yourself:

  • Wiggle test: Here, wiggle the red and black wires connected to the control module while you start the mower. If everything checks out fine and the wires are connected, visually check the printed circuit for water damage and loose connections. To save time, you may have someone help you with the wires in a wiggle test while you FOCUS on finding the issue.
  • Main fuse check: Modules have internal or external fuses, and a blown fuse cuts out the supply from the battery. First, to check the fuse, remove its zip tie and then pull the fuse from its holder. If any element in the fuse is broken or there’s a fault in the ground connection, you should have it replaced. However, if you’re unsure, you can check for continuity using your multi-meter.

A good fuse should measure near 0 ohms. On the other hand, a blown fuse will measure infinite resistance.

Check Safety Functions

Every mower even the cheapest riding mower you can find in the market has in-built safety features. Typically, sensors or switches control these features, and they are routed through the control module. Once a detector activates a safety function, your mower won’t work as usual.

The main ones to check are the brake pedal switch, blade switch, battery connection, weight sensor (to make sure a driver is sitting before the mower works).

When you jump start the engine, you should press your brake pedal. If the brake pedal doesn’t work, then you need to inspect your brake detector.

  • Remove the hood and air-duct screws.
  • Pull off the air duct and take the fuel tank and filter out of the way.
  • Pull the cable harness off the brake switch, noting the wiring.
  • Using the multi-meter probes, touch both prongs that connect to the wiring of the brake detector.

If the brake switch is okay, the multi-meter should display 0 ohms of resistance. Replace this switch if you read infinite resistance from your multi-meter.

A riding mowers engages when the blade knob is switched off or the transmission isn’t set to park. To check the blade switch, our experts recommend to do the following:

  • Take out the clutch lever mounting screws. The assembly should drop slightly when the screws aren’t in place.
  • Note the prong’s wiring and then disconnect the blade switch’s cable harness.
  • Using your multi-meter probes, touch both prongs to measure the resistance of the blade switch.

Like before, 0 ohms implies your blade switch is good, while infinite resistance means you need to replace it.

Motion detectors, switches, and sensors have in-built override functions. These functions are generally used for tests, and simply disconnecting a detector can cause an override. If you suspect your sensors are on an override, our team suggests to reconnect them before starting the device.

Replace Faulty Solenoid

Follow these steps to change a faulty solenoid:

  • First, raise the seat to get to the battery. Then, disconnect the battery terminals, starting with the negative (colored black) and then the red
  • Remove the battery from its slot. While at it, check for leaks or corrosion at the bottom and sides. Clean corrosion off the cable leads with a wire brush if they are still there after dusting.
  • Disconnect the cable harness that’s connected to the seat’s detector.
  • Pull off the battery box after removing its clips or screws.
  • Note the wiring connected to the solenoid and then disconnect the cables in any order.
  • Remove the mounting and tab both with a screwdriver.
  • Remove the faulty solenoid and replace it with the new one.
  • Finally, replace the seat, battery, and other parts.

While you can repair some solenoids, it’s often better to change them for longevity. In this way, you can still have the opportunity to place your riding lawn mower on retail in the long run given that the equipment is properly maintained.

The Starter Relay and Why a Mower Won’t Start

A lawnmower requires several amperes of electrical current to start the engine. For safety reasons, a lawnmower (and other electric-start internal combustion powered vehicles) contains two parts to the starting circuit: a start switch circuit and a relay circuit. Since an electromechanical relay can only be used for a specified number of cycles before failure, a faulty starter relay can prevent a lawnmower from starting.

Why a Lawnmower Contains a Starter Relay

A relay allows a low-power, light-duty switch to actuate or disengage the starter circuit without being directly wired to the starter circuit itself. If the lawnmower starter circuit did not contain a relay, heavy-duty wiring would have to be wired to the lawnmower starter switch. This would pose a potentially fatal shock hazard if the starter switch or starter circuit wiring became damaged. The starter switch would also be prone to electrical arcing and excessive heat, which would eventually destroy the switch and potentially damage the lawnmower.

  • A lawnmower requires several amperes of electrical current to start the engine.
  • For safety reasons, a lawnmower (and other electric-start internal combustion powered vehicles) contains two parts to the starting circuit: a start switch circuit and a relay circuit.

Why a Bad Relay Prevents a Lawnmower from Starting

When the starter switch is turned on, the switch circuit provides power to an electromagnet inside the relay. This electromagnet pulls the relay switching mechanism closed and engages the relay circuit. The relay circuit provides power from the battery to the starter.

If either the electromagnet or the switching mechanism in the relay is faulty, the relay circuit will not engage. This prevents electrical current from flowing to the starter from the battery.

Why a Bad Switch Prevents a Lawnmower from Starting

Since the switch circuit provides power to the electromagnet in the relay, the switch circuit is just as important as the relay circuit. If the switch is broken, the switch circuit will not provide electrical current to the electromagnet. Without electrical current flowing through it, the electromagnet will not work and the relay cannot be actuated.

  • When the starter switch is turned on, the switch circuit provides power to an electromagnet inside the relay.

Other Considerations

Both the switch circuit and the relay circuit require a power source and transmission lines (wires) to operate properly. If there is a break in the wire on either side of the circuit, or if the power source connection is loose or faulty, this will prevent the lawnmower from starting as well.