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How to Test a Lawn Mower Ignition Coil

By Dale Yalanovsky ; Updated September 21, 2017
Test your lawn mower ignition coil to keep your mower running smoothly.
lawnmower image by sumos from Fotolia.com

One of the symptoms of a bad lawn mower ignition coil appears when you are mowing the lawn and the mower gets hot and literally shuts off. The mower must cool down over a period of time and will start and run for awhile until it gets hot again, at which time it will shut off again. The only real way to determine if it is a bad ignition coil and not another problem is to test the coil itself.

Pull the spark plug boot off of the spark plug, and replace it with the boot of the in-line spark tester.

Plug the free end of the tester into the original spark plug boot. Push it in firmly to make sure there is a solid connection.

Start the mower when it is cold, and look through the window of the tester. Observe that there is a normal spark that allows the mower to run.

Replace the tester with the original spark plug boot and start up the engine. If possible, mow some grass to bring the mower up to operating temperature so that it shuts off again.

Replace the original wire with the in-line spark tester, and attempt to start the motor. Watch for the same intensity of a spark that you saw when the mower was cold, If there is little or no spark, the ignition coil is bad and needs replacement. If the spark is good but the mower refuses to start, it's another problem unrelated to the ignition coil.


Things You Will Need

  • In-Line Spark Tester (available at any auto parts store)


  • The best place to check for spark intensity is in a shaded or darkened area. It will be very difficult to see a spark with the tester in full sunlight. Inside an unlighted garage or at dusk is the best way to observe a spark through the tester's window.


  • Pulling off the spark plug boot and connecting the spark tester when the motor is hot is best accomplished with a pair of gloves.

About the Author


Dale Yalanovsky has been writing professionally since 1978. He has been published in "Woman's Day," "New Home Journal" and on many do-it-yourself websites. He specializes in do-it-yourself projects, household and auto maintenance and property management. Yalanovsky also writes a bimonthly column that provides home improvement advice.