How To Test an Ignition Coil in a Vehicle?

The ignition coil is an important part of your vehicle. Also known as spark coil, this induction coil is a … Continued

The ignition coil is an important part of your vehicle. Also known as spark coil, this induction coil is a part of the ignition system of your car. This means, when you start the car, it powers the battery’s low voltage and converts it into a high voltage that is enough to create a spark in the spark plugs.  In turn, this will ignite the fuel and start the car.

The main job of the ignition coil and the system as a whole is to increase the 12 volts of car’s battery into the very high voltage, so it can ignite the fuel mixture present inside the combustion chamber. The role of the coil is to produce this high voltage that is right enough to power the car. As you can see, the ignition coil plays an important role in the overall functioning of the car.

So, it is important that this coil works well as you cannot even start the car without it! It is a good idea to test this ignition coil if your car does not start for any reason.

Let’s now see how you can test.

There are two kinds of test available to test your ignition coil, and they are, spark plug test and bench test. You can choose to do one of these tests or both, just depends on your preferences. But before you do any test, it is important to take certain precautions.

replacing spark plugs in the engine


Testing the engine of your car is more dangerous than you may think. Make sure you have the right safety equipment such as safety goggles to prevent any untoward accident. Also, make sure you are not wearing any loose clothing and your hair is tied back well. These precautions are necessary because your engine produces electricity, and it is also better to be safe than sorry!

Spark Plug Test

After you’ve taken all the precautions, you can do the spark plug test.

As a first step, remove the wire from the plug. If you are not sure which wire or if you are doing this test for the first time, keep your car’s manual with you. Identify the right wire based on instructions from the manual and remove it.

Next, remove the spark plug with the help of a spark plug socket. Never attempt to do it with bare hands.

After taking out the spark plug, attach the plug wire back. Hold the plug wire using insulated pliers, and allow the bare end of the spark plug to touch a grounded surface. such an exposed metal area. Take help from your partner or someone else, and ask them to start the ignition. When the key is turned on, you should see a bright blue spark at the end of the spark plug.

Obviously, if you don’t see the coil, it means your ignition coil is not working and it needs to be replaced.

One downside with this test is that it is hard to know if the ignition coil is not working so well. In other words, you may see a spark, but it can be feeble. As non-technicians, it is hard to distinguish whether the spark was bright or feeble. This is why the bench test is a more thorough way of testing your ignition coil.

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car spark plugs

Bench Test

This bench test is all about the primary and secondary windings of your car. Before you begin, keep the car manual handy and make a note of the normal reading for each of these two windings. In general, the primary winding will have a reading of 0.75 to 0.81 ohms while the secondary winding will have a value of 10,000 to 11,000 ohms. Check your manual for the exact values.

Now, to check this resistance, attach the ohmmeter to the outside poles of the primary winding.  For the secondary winding, attach one end to either of the poles and the other end to a central high tension terminal. Then check the values.

As you can see, this test is more thorough as it gives the exact state of the ignition coil. Even if the readings are a little off from your manual, replace the ignition coil as these off readings could indicate that it is weak.

Thus, these are the two way to check whether the ignition coil in your engine is working fine. When your tests show that you have to replace them or if you feel the coil is weak and needs to be replaced, get in touch with a reputed auto repair shop to do this job for you.


  1. How to Diagnose and Test an Ignition Coil – AA1 Car
  2. How to Test Ignition Coil in a Vehicle – doityourself