Automotive Diagnostic Tips And Techniques: The Ignition Coil

Knowing the theory of how something works is important, but only to a certain extent. Because the main reason you're here is to learn how to test something not to learn what metals it's made of or how the magnetic field is interrupted by the thing-a-ma-jig and blah, blah, and blah. You don't want to reverse engineer the stupid thing, you just want to solve the problem!!!

I have always been amazed at the amount of baloney and useless information you'll find on the Internet about anything automotive. I don't give a crap if it's made of plastic or titanium or whatever!!! I want to know how to test it. Period.

Finding that testing information can sometimes be hard or next to impossible. Which makes knowing how something works that much more important. This knowledge will help you to troubleshoot/diagnose the automotive component in question as either being good or being bad whether you have the diagnostic manual next to you or not. Therefore, the most important theory to learn and to know is how the component should behave in the overall system it's a part of, and not only that, but WHAT makes it behave. Case in point: the ignition coil.

In Spanish You can find this tutorial in Spanish here: Cómo Funciona La Bobina De Encendido (at:

What The Ignition Coil Needs To Fire Off Spark

OK, the most important ‘theoretical’ things we have to know about life. No, wait a minute, wrong web site, I mean the ignition coil are:

  1. It needs battery voltage.
  2. It needs a Switching signal that's provided by a Switching device.
    • This Switching device is either called the ignition control module (ICM) or Power Transistor or Igniter or this function is handled by the fuel injection computer itself.
    • The Switching device is responsible for ‘switching’ the Primary Current (which is the technical name for 12 Volts), flowing thru' the ignition coil ON and OFF.
    • This switching ON and OFF is accomplished by interrupting the Primary Current's Ground path.
    • This switching ON and OFF of the Ground is what makes the ignition coil fire off spark for the spark plugs.
  3. The Switching device needs a Triggering signal from a Triggering device to let it know when to create and feed the Switching signal to the ignition coil.
    • This Triggering device is usually a crankshaft position sensor, altho' it may be called by a different name (depending on manufacturer) like: distributor pick up coil, crank angle sensor, profile ignition pickup (PIP) sensor, etc.
  4. That if it's receiving all of the aforementioned things, it should spark.
    • Every signal can be tested with simple and inexpensive tools.
    • You don't need an automotive scan tool to test these components.

With info like this, you'll be ready to take over the world!!!! But if you still want the actual theory of how it works, you can look it up on Wikipedia (you could probably build one from scratch with the info, too).

Types Of Ignition Coils

Automotive Diagnostic Tips And Techniques: The Ignition Coil Automotive Diagnostic Tips And Techniques: The Ignition Coil
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OK, getting back to the world in which you and I live, what throws a wrench into our ‘equation’ of how the ignition coil should work, is that they are set up in so many different ways. Now, it's not that they use different laws of physics to work, it's just how they go about implementing the creation of and feeding of the Switching signal. For example:

  1. Some ignition coil connectors have only two wires.
  2. Others have three or four wires coming out of the connector.
  3. Some are controlled by an external control module.
  4. Some have the control module (called the Power Transistor or Transistor) integrated inside of them.

Some crazy stuff, huh? The good news is that there are some basic things that apply to them all for them to produce the required spark for combustion. Not only that, they can be tested on the car with some very simple and easy tests!

OK, to effectively understand how to test the ignition coils, independent of how many wires are coming out of their connectors, we need to delve into useful and working ‘theory’ of the ignition system. We need to know about the Primary and Secondary circuits of the ignition coil. I'll also go into some detail about the relationship between the ignition coil and the ignition control module and crankshaft position sensor. Lets turn the page to learn more.

What's The Ignition Coil's Primary Circuit?

Simply put, the Primary circuit is the wire or wires that deliver 12 Volts to the positive (+) terminal of the ignition coil.

It also includes the Primary windings inside the ignition coil. And lastly, the circuits involved in taking this current to the ignition control module (or Power Transistor or computer) from the ignition coil's negative terminal.

The 12 Volts that flow thru' this circuit are called the Primary current. OK, so now you know that the ignition coil gets 12 Volts from the Primary circuit, but what happens next? Let's find out in the next subheading.