How To Test 2-Wire Coil-On-Plug (COP) Ignition Coils

There are two main types of Direct Ignition Systems used on all of the cars and trucks on the road today:

  1. Coil pack type.
  2. Coil-On-Plug. And this type can be divided into the three obvious types you'll see on the road today:
    • With two wires (circuits) in their connector.
    • With three wires (circuits) in their connector.
    • With four wires (circuits) in their connector.

This article will shed some light on the 'working theory' and the testing of the Coil-On-Plug type with two wires (circuits) in its connector (the article dealing with the three wire (circuit) Coil-On-Plug type can be found here: Testing And Troubleshooting 3-Wire COP Ignition Coils). Knowing this ‘theory’ will help you to understand the why and how of many of the tests that are performed on this type of system.

This article is a general overview of the COP Coil tests. To see the specific COP Coil articles:

In Spanish You can find this tutorial in Spanish here: Cómo Probar Bobinas de Encendido Individuales de 2 Cables (at:

As you'll see, this ‘theory’ stuff isn't hard to understand. And the tests to test this type of ignition coil are easy and simple.

Not only that, you can apply this testing info and/or theory to just about anything rolling around on pavement on the planet with this type of Coil-On-Plug ignition system. So whether it's a Ford, a Chrysler, a Nissan, a Chevrolet, a Mazda, etc., this ‘working theory’ and the testing tips and techniques you'll learn here will apply.

Symptoms Of A Bad Coil-On-Plug

The advantage of having and knowing this information (working theory and tests) is that it'll make your life a whole lot easier when diagnosing the most common symptoms of a bad Coil-On-Plug ignition coil:

  1. Ignition Misfires.
    • Without codes lighting up the check engine light.
    • With codes lighting up the check engine light.
    • On OBD2 and non-OBD2 vehicles.
    • On 4, 6, 8 cylinder engines.
  2. NO START condition.
  3. Rough idle.

I recommend, if you haven't already read, the following primer on ignition coils: Automotive Diagnostic Tips And Techniques: The Ignition Coil This article will shed some light on some of the terms used in this article.

Using An LED Light To Test The Coil-On-Plug

As I've already mentioned, the type of Coil on Plug ignition coil that we'll be testing has two wires in its connector. The testing of these two circuits is done in part while the engine is being cranked.

Testing these circuits can be accomplished in several different ways. From using expensive testing equipment like an oscilloscope to using something as a simple test light or an LED light or a multimeter.

Since so few people own an oscilloscope, the primary way this article deals with these tests is using a simple and inexpensive LED light. As mentioned before, you'll see just how fast, easy and simple these tests are.

Not only that these are real world testing methods, tips and techniques that I have used and still use day in and day out with great results.

Thru'-out this article you'll see photos of engines with a Coil on Plug type system. These photos are just for a visual reference. The info in this article will apply to any vehicle with the two wires in the connector of the Coil-On-Plug ignition coil.