How to Check an Ignition Coil With a Volt Meter

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If you suspect that the ignition coil on your engine is malfunctioning, you can test it at home. You will need a digital multimeter (also known as a volt/ohm meter) with an ohms setting on it so that you can measure the resistance of the coil. Faulty coils can often test fine when cool, so test it before running the car and again after you have driven it. If the coil in your car is defective, you can get a new coil at most auto parts stores or the dealer.

Remove the negative battery cable from the battery. Use a wrench to loosen the retaining bolt and lift the cable end off the battery terminal.

Locate the coil on your engine. The coil may be cylindrical and have a large wire coming out of it, or it may be a flat square-shaped unit, but it will still have a large wire similar to a spark plug wire attached to it.

Remove the large wire from the high-tension terminal. This wire looks like a spark plug wire and pulls straight off the coil.

Remove the secondary wires from the coil. On older coils, you need to remove the nut that holds the wires on. On newer coils, they are typically a plug you can disconnect.

Set the multimeter to read ohms and test the resistance in the primary and secondary sides of the coil. Place the red test lead on one connector and the black on the other. Read the resistance across the two connectors. This is the primary resistance and should be between .7 and 1.7 ohms.

Place one test lead on the negative side of the coil and the second in the high-tension terminal. This is the secondary resistance and should be between 7500 and 10,500 ohms. If the readings are outside that range, remove and replace the coil.

Reinstall the wires on the terminal and plug the large coil wire into the high-tension terminal. Install the negative battery cable on the battery terminal and tighten the bolt with a wrench.

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