Coil on Plug ignition systems are becoming the standard ignition system on most makes. Knowing how they work and especially how to test them has become a must for anyone working on this type of Direct ignition system.

I'm gonna' share with you simple and effective testing tips and techniques for testing Coil-on-Plug ignition coils that I've used with a lot of success. The tests for testing Coil on Plug ignition coils are not hard at all. And more importantly, you don't need expensive testing equipment either.

This article covers Coil on Plug ignition coils on a general basis... if you want to see specific Make, Model and Year tests you can take a look at the following articles:

  1. How To Test The Coil-On-Plug Ignition Coil 3.0L Honda Accord - Odyssey.
  2. How To Test The Coil-On-Plug Ignition Coil of the 04-05 Suzuki Verona.
  3. How To Test The Coil-On-Plug (COP) Ignition Coils on Suzuki Swift, Vitara and Chevrolet Metro, Tracker.

En Español Puedes encontrar este tutorial en Español aquí: Cómo Probar Bobinas de Encendido Individuales de 3 Cables (en: easyautodiagnostics.com/es/).

Honda Accord Coil-on-Plug System

Common Symptoms Of A BAD Coil on Plug

The most common symptoms of a BAD Coil-on-Plug ignition coil or Coil-on-Plug ignition system faults are:

  1. misfire codes that will light up the CHECK ENGINE light (if the vehicle is modern enough to support Misfire Self-Diagnostics).
  2. A rough idle due to the Misfire Condition itself.
  3. A NO START condition.

As you might already know, there are several types of coil-on-Plug ignition systems. The three most basic types are the following:

  1. Each ignition coil has two wires (circuits) in the connector.
  2. Each ignition coil has three wires (circuits) in its connector.
  3. Each ignition coil has four wires (circuits) in its connector.

This article deals with the testing of the three wire type of coil-on-Plug ignition coil. To find out how to test the Coi-on-Plug type with two wires in the connector, you can follow this link: Testing Tips and Techniques for Coil-on-Plug Type 1.

Why does this type have three wires in the connector instead of just two? We're gonna' explore the answer in some detail in this article. Knowing what each wire (circuit) does is the key to successfully testing them. And this 'working theory' can be applied to any vehicle with a Coil on Plug ignition system where the connector of each ignition coil has three wires in it.

What the Three Wires Do

The following are the basic descriptions of each of the three circuits on each individual ignition coil on this Coil on Plug ignition system.

  1. Power Circuit.
  2. Ground Circuit.
  3. Triggering Signal Circuit.

If any one of these three inputs is missing, this type of Coil-on-Plug will not spark.

You might be asking yourself: So how are these Signals tested? Do I need a scan tool (Automotive Diagnostic Scanner) test them with? How hard are these tests? Let's turn the page and find out all of the answers to these questions.

This type of coil has three wires (circuits) in its connector. You're gonna' learn simple, easy and effective tests to diagnose a BAD Coil-on-Plug ignition coil. No Scan Tool (Automotive Diagnostic Scanner) is required to test the Coil-on-Plug ignition coils.

You'll need a digital multimeter that can read Hertz frequency or you can use an oscilloscope. This article concentrates on using a digital multimeter to test the Coil-on-Plug ignition coil with three wires in its connector.

Suzuki Swift Coil-on-Plug System

Before we go into the specific tests, we need to know just a little ‘working theory’ of how this type of coil-on-Plug System works. Knowing this simple working theory will help you to understand the why and how of the tests that are done on this type of coil on Plug ignition system.

The information is broken up into three headings which are: The Power Circuit, The Triggering Signal, and The Ground Circuit. OK, let's start...

The Power Circuit

The Coil-on-Plug ignition coil has three wires coming out its connector. One of those wires (circuits) is the one that delivers 12 Volts to the coil.

Usually, the same fuse or relay feeds all of the Coil-on-Plug ignition coils. And this circuit can be tested with a multimeter or a test light. Both methods work. Testing for Power is usually the second test that's performed after the spark test.

The Triggering Signal Circuit

One of the major differences of this type of Coil-on-Plug ignition system (with the three wires in the connector of the ignition coils) is that it does not receive a Switching Signal at all. It receives a Triggering Signal instead. You might be asking, what the heck is a Triggering Signal?

To be able to answer this question, we need to know that the ‘Ignition Control Module’ is located inside the Coil-on-Plug ignition coil itself (in this type of Direct Ignition System). It's not an ‘Ignition Control Module’ per se, but a transistor that provides the ignition control module function.

Thus the Triggering Signal is the Signal that tells this transistor the exact time to make the ignition coil spark. This Signal can be tested by two methods. Both are easy to do. One is by using a multimeter that's capable of reading Hertz Frequency. And the other is using an Oscilloscope.

As mentioned before, we're gonna' concentrate on the multimeter test. This is an easy, fast, and proven method that works..

On a last note, if the terms ‘Switching Signal’ and ‘Triggering Signal’ left you a bit confused, I recommend reading: How does an Ignition Coil Work? This article will shed more light on the matter.

The Ground Circuit

The other major difference in this type of coil-on-Plug ignition coil is that one of the three wires is a ‘full-time’ Ground Circuit. By ‘full-time’ I mean that this circuit is not interrupted (opened) by any Ignition Control Module like in a conventional ignition coil.


As you may already know, the conventional Distributor type ignition coils and the two wire in the connector Coil-on-Plug ignition coils do not have a ‘full-time’ ground circuit. This is because the Ignition Module (whether it's integrated into the ECM or not) controls this ground circuit by Switching it ON and OFF.

This Coil-on-Plug ignition coil (with the three wires in the connector) has the Ignition Module integrated into the coil itself. This ‘full-time’ Ground wire is for the transistor (Ignition Module) itself.

Now that we have learned the purpose of each wire in this type of coil-on-Plug, lets jump into the actual tests.