How To Test An Ignition Coil: 14 Steps (with Pictures) - WikiHow

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1 Remove the ignition coil from the vehicle. The test above isn't the only way to determine whether the ignition coil in your vehicle is functioning as it should. If you have access to a piece of electrical equipment called an ohmmeter, which measures electrical resistance, you can measure the effectiveness of your ignition coil in a definitive, quantifiable way, rather than in the somewhat subjective way described above.[6] X Research source However, to begin this test, you'll need to remove the vehicle's ignition coil so that you can easily access its electrical terminals.
- Refer to your service manual for precise instructions on removing your ignition coil. Usually, you'll need to disconnect it from the distributor wire, then unscrew it from its mounting with a wrench. Ensure your vehicle is turned off and has had a chance to cool before beginning this process.[7]
Diagnose engine issues quickly. "My old Honda started having trouble turning over recently. I used the steps in this guide to test the ignition coil, and it turned out the coil was still working fine. Now, I can focus on other potential issues instead of replacing parts that are still good. This article helped me quickly figure out what's wrong with my car." - Sander W. Confirm coil failure before buying a new one. "I was worried there was something wrong with the ignition coil in my Civic because the engine had been misfiring occasionally. I did the resistance test described here and got a reading that was outside the factory specs for my coil. Now I know for sure that I need to replace the bad coil instead of just guessing at the problem." - Garold M. Learn the right way to test parts. "When my engine started sputtering, I had no idea where to even start troubleshooting. This article walked me through how to systematically test the ignition coil and other components. Now, I know the proper bench testing procedures, which will really come in handy for diagnosing issues down the road." - Lee F. Avoid unnecessary repairs with targeted testing. "My car was having some ignition issues, so my first instinct was to just replace the whole system. But after reading this, I tested just the coil, specifically using these steps. Since that single part tested badly, I can swap in a new coil without wasting time and money replacing other stuff that's still working fine." - Kundai M. Did you know that wikiHow has collected over 365,000 reader stories since it started in 2005? We’d love to hear from you! Share your story here.
2 Find the resistance specifications for your ignition coil. Every vehicle's ignition coil has its own unique specifications in terms of the electrical resistance within the coil.[8] X Research source If your coil's actual resistance levels fall outside of these specifications, you'll know that your coil is damaged. Usually, you'll be able to find the resistance specifications unique to your vehicle by consulting your service manual. However, if you can't find it here, you may find success by contacting your dealership or by searching online vehicular resources.
- Generally speaking, most automotive coils will have a resistance reading of about .7 - 1.7 ohms for the primary winding and 7,500 - 10,500 ohms for the secondary winding.
3 Position the leads of the ohmmeter on the poles of the primary coil. The distributor will have three electrical contacts - two on either side and one in the middle. These may be either external (jutting out) or internal (sunken in) - it makes no difference. Turn on your ohmmeter and touch one lead to each of the outer electrical contacts. Record the resistance reading - this is the resistance of the coil's primary winding.
- Note that some newer models of ignition coil have contact configurations that differ from this traditional arrangement. Consult your vehicle's manual for information if you are unsure which contacts correspond to the primary winding.
4 Position the leads of the ohmmeter on the poles of the secondary coil. Next, keep one lead on one of the outer contacts and touch the other to the central, inner contact of the ignition coil (where the main wire to the distributor connects). Record the resistance reading - this is the resistance of the coil's secondary winding.
5 Determine whether the readings you recorded fall within your vehicle's specifications. Ignition coils are delicate components of a vehicle's electrical system. [9] If either the primary or secondary windings are even a little outside of your vehicle's specifications, you'll want to replace your ignition coil, as your current one is likely damaged or malfunctioning.