How to Test the Ignition Module for John Deere Lawn Tractors

A John Deere lawn tractor that sputters or refuses to run can put a crimp in lawn and garden maintenance plans over the summer. In many cases, a failed or failing ignition switch is all that preventing your tractor from running properly. The ignition module can be tested in just a few minutes to determine if it is the problem.

Tractor with a spray device for finely dispersed fertilizer. Tractor on the sunset background. Tractor with high wheels is making fertilizer on young wheat. The use of finely dispersed spray chemicals
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How to Test the Ignition Module for John Deere Lawn Tractors

How the Ignition Module Works

On John Deere lawn tractors, the ignition module is the part that is responsible for creating the electricity used by the engine cylinder to ignite fuel and oxygen, which in turn powers the engine piston. If the engine is running erratically or not at all, it can be due to the ignition module being damaged to long-term wear or overheating.

Safely Park and Secure the Tractor

Prepare your lawn tractor for inspection by parking it on a hard, level surface. Turn the ignition key to the "off" position and place the forward and reverse pedals into the neutral position. Set the parking brake and place a wheel block under the right front tire. Raise the hood on the lawn tractor and secure it in the open position.

Locate the Spark Plug Wire

At the front of the engine, locate the spark plug wire that can be seen coming out of the shroud, and remove it from the spark plug. Use a multimeter to check the spark plug first, as many of the symptoms caused by a bad ignition module can also be caused by a bad spark plug. If the spark plug is good, continue on to check the ignition module. If it is bad, replace the spark plug and test the tractor. If the problem persists, continue on to test the ignition module.

Test the Ignition Module

Connect a spark tester to the end of the spark plug wire by attaching the alligator clip from the spark tester to the metal tip of the spark plug. Wear gloves in case a spark jumps while you are completing this step. Set the gap to 4.2mm on top of the spark tester by using the adjustment knob. Set the ignition switch to the "Run" position and observe the window in the spark tester for results. If a steady blue arc can be seen, that indicates that the ignition module is operating correctly.

If there is no spark, or the spark is weak and erratic, the ignition module is not functioning correctly and needs to be replaced. Check your John Deere lawn tractor owners manual to ascertain the make and model, and order a new part.

Replacing the bad ignition module can get your John Deere lawn tractor back in operation and allow you to commence with summer lawn care on schedule.