How is an ignition coil tested?


Quick Answer

Although there are a number of suggested tests for the ignition coil while it is still attached to a car, the only accurate way of testing a coil is on a bench using a multimeter in the resistance setting. The ignition coil has two coils of wires, called windings. The meter quickly displays if either winding is bad.

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Full Answer

The primary winding collects the electricity needed to create the spark and the second sends it to the distributor. If either is bad, the coil is failing. Using a multimeter on a disconnected coil provides the data needed to determine its health. Start by checking the resistance between the coil's side terminals. With all but a few coils, the meter should show 0.75 to 0.81 ohms of resistance. Next, check the resistance between the center terminal and either side terminal.

A good coil reads between 10,000 and 11,000 ohms. Replace the coil if there is any significant deviation from these numbers. Cars with a bad coil often run or idle rough. During cold weather, starting the car becomes difficult. As the coil continues to deteriorate, the vehicle eventually fails to start. Replacing a defective coil helps the vehicle to start quickly and run smoothly, increasing its fuel efficiency.

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