April 1, 2013

How to replace a lawn mower safety switch

By Lyle Weischwill
How to replace a lawn mower safety switch

This DIY lawn mower repair guide has step-by-step instructions for how to replace a lawn mower engine safety switch. The safety switch stops the engine when you release the control bar on the handle, by stopping the ignition coil from sparking; it also has a brake pad to slow the flywheel. If the switch isn't working, the ignition coil won't spark the spark plug, and the lawn mower won't start. 

To determine if the switch is the problem, remove the kill wire from the ignition coil and check for engine spark. If there's spark, replace the engine safety switch with the manufacturer-approved replacement part

A broken safety switch can also make the ignition coil keep sparking after you release the handle lever. In that case, remove the spark plug until you can replace the mower engine safety switch.

This procedure works for Briggs & Stratton engines that power Craftsman, Poulan, MTD, Troybilt, Toro, Husqvarna, Murray, Yard-Man and Snapper walk-behind lawn mowers.

Quick links
Tools required
Phillips screwdriver
Socket wrench
5/16-inch socket
3/8-inch socket
Needle-nose pliers
Slot screwdriver
Work gloves
Repair difficulty
Time required
30 minutes or less
Repair difficulty
Time required
30 minutes or less

Instructions

01.

Disconnect the spark plug wire

Let the engine cool.

Wear gloves to protect your hands.

Disconnect the spark wire so there's no chance that the mower could accidentally start.

Disconnect the lawn mower spark plug wire.

Disconnect the lawn mower spark plug wire.

02.

Remove the engine cover

Remove the starter rope from the rope guide. If the rope won't slip past the guide and the handle, loosen the guide.

Remove the screws securing the engine cover to the engine. Slide the rope through the hole in the engine cover.

Remove the starter rope from the guide.

Remove the starter rope from the guide.

Remove the engine cover.

Remove the engine cover.

03.

Remove the fuel tank

Remove the screws that secure the fuel tank to the engine.

Lift the tank off, being careful to keep the fuel tank upright so it doesn't leak.

Remove the fuel tank.

Remove the fuel tank.

04.

Remove the dipstick tube

Remove the screw that secures the dipstick tube to the housing.

Remove the dipstick tube from the engine and plug the hole with a paper towel to keep debris from falling into the engine.

Remove the dipstick tube.

Remove the dipstick tube.

05.

Remove engine blower housing

Remove the bolts securing the blower housing to the engine and remove the housing from the engine.

Remove the blower housing.

Remove the blower housing.

06.

Remove the safety switch

Take a digital photo of how the zone control cable connects to the engine safety switch.

Use a pair of needle-nose pliers to squeeze the tabs on the cable housing. Pull the cable housing to remove it from the safety switch bracket.

Press down on the tab that attaches the kill wire to the safety switch and disconnect the wire from the safety switch. Remove the 2 mounting screws that secure the engine safety switch to the engine.

Remove the safety switch.

07.

Install the new safety switch

Position the new safety switch on the engine and secure it with the mounting screws.

Reinstall the kill wire by pushing down the locking tab and inserting the wire into the safety switch. Release the tab. Reconnect the zone control cable and work the engine control bail on the handle to make sure it works smoothly.

08.

Reassemble the mower

Position the engine blower housing on the engine and bolt it into place.

Remove the paper towel from the dipstick opening, slide the dipstick into the engine and secure it with the screw.

Feed the starter rope handle through the engine cover up to the rope guide.

Position the engine cover on the engine and screw it into place.

09.

Reconnect the spark plug wire

Attach the spark plug wire and make sure the mower works properly.

Warning: Undertaking repairs to appliances can be hazardous. Use the proper tools and safety equipment noted in the guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs should only be performed by a qualified technician.
Symptoms for gas walk-behind mowers

Choose a symptom to see related walk-behind mower repairs.

Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel
Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up
Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, bad ignition coil
Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key
Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade
Repair guides for gas walk-behind mowers

These step-by-step repair guides will help you safely fix what’s broken on your walk-behind lawn mower.

How to replace a lawn mower ignition coil on an OHV engine

Replace the ignition coil if it isn't sending electric current to the spark plug when you pull the recoil starter rope.

Repair difficulty
Time required
 30 minutes or less
How to replace a lawn mower flywheel key on an OHV engine

The flywheel key couples the flywheel to the engine crankshaft. Replace the flywheel key if it's broken.

Repair difficulty
Time required
 60 minutes or less
March 1, 2016
By Lyle Weischwill
How to replace a lawn mower drive cable

The drive cable engages the transmission to spin the drive wheels and move the mower across the grass. Replace the drive cable if it's broken or frozen up inside the sheath.

Repair difficulty
Time required
 60 minutes or less
Articles and videos for gas walk-behind mowers

Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.

May 31, 2019
How to tune up a lawn mower video
By Erin Hynes

See how to tune up your mower once a year to keep it running well.

February 1, 2016
6 weeks to a better lawn
By Erin Hynes

Do these 5 things this spring for a lawn that's healthier all summer.

April 1, 2015
How to keep grass clippings from sticking to a mower deck
By Erin Hynes

Prevent your mower deck from rusting by following our advice for keeping grass clippings from sticking.