How to Check a Lawn Mower Coil With an Ohmmeter

The coil on a lawnmower engine provides a continuous high-voltage charge to maintain combustion in the engine. The initial spark to start the engine is provided by the spark plug, which is wired directly to the coil. Once the engine is running, the flywheel over the coil provides a continuous electric pulse. If the coil burns out, the engine will not run. Testing the coil for circuit continuity takes less than an hour using basic tools and an ohmmeter.

Nut driver set
Needle-nose pliers
Ohmmeter.

Instructions

- 1
  Shut off the mower and wait for the engine to cool if it has been running.
- 2
  Pull the rubber cap off the tip of the spark plug.
- 3
  Remove the molded cowling over the engine, using the nut driver to remove the bolts, if your mower is equipped with a cowling to protect the engine from leaves and grass clippings. If there is no cowling, skip this step.
- 4
  Extract the three to four bolts holding the flywheel to the top of the engine, using the nut driver and the appropriate nut-driver socket to fit the bolts on your model. A 1/2-inch bolt is common on many mower engines.
- 5
  Take off the flywheel to see the coil underneath. One terminal on the coil is connected to the insulated wire for the spark plug. The other terminal attaches to a ring connector on the engine.
- 6
  Place one of the test rods on the ohmmeter inside the rubber cap on the wire that attaches to the spark plug. Verify the test rod is touching the metal cap inside the rubber.
- 7
  Place the remaining ohmmeter test rod on the other coil terminal where it attaches to the ring connector. If the ohmmeter registers zero or the dial moves to the infinity range, represented by a figure-8 turned on its side, then the coil is defective.

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