How to Test a Lawn Mower Solenoid

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Every lawn mower or riding mower that has a starter will also have a starter solenoid. Essentially, every starter solenoid acts like an electromagnetic switch. When a key is turned or a button pushed, electricity enters a solenoid in a regular starter circuit. A switch inside then makes a positive connection and allows electricity to flow to the starter motor. When a solenoid goes bad, the circuit cannot be completed, and the starter will not get any electricity to start the motor.

Things You'll Need

  • Wrench
  • Multimeter
  • Find the solenoid on your lawn mower. Trace the large red or positive cable that comes off the battery to the first junction to which it is connected. The battery cable will end at the solenoid and be connected to an electrical post. Leading away and on the other side of the solenoid will be another large red cable. This leads to the starter motor. Although there will be one or two other wires connected to the solenoid, none will be as large as the battery and starter cables.

  • Remove the starter cable from the solenoid by using the proper sized wrench. Keep the battery cable mounted and in place.

  • Set your multimeter to 20 volts DC. Turn the ignition to "on" and touch the black or ground probe to the chassis, and then touch the red or positive probe to the post where the battery cable is connected. Read the multimeter and verify that there is a voltage reading of approximately 12 volts.

  • Remove the red probe from the battery side, and touch the electrical post where the starter cable has been removed. Turn the ignition to the "start" position and read the voltage on the multimeter. The voltage should be exactly the same as on the battery side. If there is no voltage showing, the solenoid is no longer working and needs to be replaced.

Tips & Warnings

  • There are two favorite backyard mechanic ways to test a solenoid without a multimeter. The first involves gently tapping the top of the solenoid with a small hammer when the ignition switch is in the "start" position. This often will free a sticking switch, trigger the connection, and start the mower.
  • Another way is to use a screwdriver to bridge the gap between battery post and starter post. Just place the ignition into the "on" position, touch a screwdriver simultaneously to the battery and starter motor posts on the solenoid, and if the starter motor turns over, you know the solenoid is bad. If you try this, do not touch the screwdriver with your bare hand, or you will get a bad electric shock and possibly a burn. Wear work gloves, or, better yet, don't try this.
  • Always make sure your lawn mower is in neutral and the brakes are locked before trying any of these solenoid testing procedures.

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References

  • Photo Credit TONDEUSE AUTOPORTEE ref 1400 image by Marie-Thérèse GUIHAL from Fotolia.com
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