Testing The Coil-On-Plug Triggering Signal
So far we've learned how to test the Coil-On-Plug ignition coil for spark, its Power Circuit and its Ground Circuit. Now I'm gonna' show you an easy test to verify the Coil-On-Plug's Triggering Signal using a digital multimeter.
Each individual ignition coil on this Coil-On-Plug system has an Ignition Control Module located in it. This ignition module is usually referred to as the Transistor.
Each Transistor (within the each ignition coil) needs this Triggering Signal to know the exact time to make the ignition coil spark. This high frequency pulse that we're calling the Triggering Signal comes from the ECM (Fuel Injection Computer) and can only be measured with an oscilloscope or a Digital Multimeter that can read Hertz frequency.
Unlike the Power and Ground Circuits that are shared by all of the Coil-On-Plug ignition coils, each individual Coil-On-Plug ignition coil has its own Triggering Signal Circuit running to the ECM.
And as you have already deduced, if this Triggering Signal is not present the Coil-On-Plug ignition coil will not spark.
How To Test The Triggering Signal
This signal CAN NOT be tested with an LED or a test light. Only an oscilloscope or a Digital Multimeter (with the capability of reading Hertz Frequency) can be used. And well, as mentioned all along, we're gonna' use a Digital Multimeter for our tests.
I have narrowed down the most common results of this test and their causes:
- You got Signal.
- If (after confirming the presence of voltage and Ground) the multimeter did confirm the presence of the Triggering Signal the Coil-On-Plug is bad.
- You got No Signal at one Coil-On-Plug ignition coil
- The most common cause is an open in the Triggering Signal Circuit of that specific coil.
- The good news is that you have just eliminated the COP ignition coil itself as the source of the problem.
- Replacing the Coil-On-Plug ignition coil with a new one will not solve the problem since without the Triggering Signal the new one will not spark.
- You got No Signal at any of the Coil-On-Plug ignition coils
- The most likely cause is the crankshaft position sensor is defective. Again, this is usually the most common cause.
- Or the ECM (Fuel Injection Computer) is bad. Very rare, but it does happen. Further tests are required to make sure but that are beyond the scope of this article.
Coil-On-Plug Summary Of Tests
This is the Summary of what you've learned about testing Coil-On-Plug ignition coils (with three wires in the connector) in this article:
- What each of the three wires (circuits) does on the Coil-On-Plug ignition coil.
- One is the Power Circuit.
- Another is the Ground Circuit.
- The remaining one is the Triggering Signal Circuit.
- How to test the signal that is present in each Circuit.
- The Power Circuit can be tested with a multimeter or test light.
- The Ground Circuit can be tested with a multimeter or test light.
- The Triggering Signal Circuit MUST be tested with a multimeter capable of reading Hertz Frequency or an Osciloscope.
- That each individual Coil-On-Plug has the Ignition Control Module integrated within.
- This Ignition Control Module is usually referred to as the Transistor.
- That these tests are easy and simple and that:
- A scan tool is not required to test the individual Coil-On-Plug ignition coils.
As mentioned all along in this article, this info applies to any vehicle that has a Coil-On-Plug ignition system with three wires in the connector of each individual coil.
More How To Test The Ignition System Articles
The following articles (within this site) will shed some more light on ignition systems.
- NO START Diagnostic Tips.
- Ignition System Basics.
- Testing an Ignition Coil Pack.
- Testing a Coil-On-Plug Ignition System.
- Case Study of a Does Not Crank Condition.
- Case Study of an Ignition Misfire Diagnostic.
- Case Study of an Cranks but Does Not Start.
- The HEI Spark Tester.
If this info really saved the day, buy me a beer!