If you suspect that your engine’s ignition coil is malfunctioning, you can test it at home. You will need a digital multimeter (also known as a volt/ohm meter) with an ohm setting in order to measure the resistance of the coil. Read on and discover how to check an ignition coil with a voltmeter.
How to check an ignition coil with a voltmeter
Bad coils can often be tested ok when cold, so test them before you start the car and again after you’ve driven it. If your car’s coil is faulty, you can get a new coil at most auto parts stores or your dealership. Follow the steps below to check the ignition coil using a voltmeter.
Remove the negative battery cable. Use a wrench to loosen the retaining bolt and lift the end of the cable off the battery terminal.
Locate the coil on your motor. The coil can be cylindrical and have a large wire coming out of it, or it can be a flat square shaped unit, but will still have a large wire similar to a spark plug wire attached to it.
Remove the large wire from the high voltage terminal. This wire looks like a spark plug wire and pulls directly on the coil.
Remove the secondary wires from the coil. On older coils, it is necessary to remove the nut that holds the wires. On newer coils, they are typically a plug that can be unplugged.
Set the multimeter to read ohms and check the resistance on the primary and secondary sides of the coil. Put the red test lead into one connector and the black one into the other. Read the resistance across the two connectors. This is the primary resistance and should be between 0.7 and 1.7 ohms.
Place one test lead on the negative side of the coil and the second on the high voltage terminal. This is the secondary resistor and should be between 7,500 and 10,500 ohms. If the readings are outside of that range, remove and replace the coil.
Reinstall the wires into the terminal and plug the large wire from the coil into the high voltage terminal. Install the negative battery cable to the battery terminal and tighten the bolt with a wrench. With this you will have checked an ignition coil with a voltmeter!