How To Test The COP Coils (GM 4.8L, 5.3L, 6.0L, 8.1L)

Testing the GM Coil-on-Plug ignition coils on your pick up truck or SUV is pretty simple and this article will show you just how to do it.

Every step is explained in plain English and with photos to guide you every step of the way. So if your GM pick up or SUV or van is suffering a misfire condition due to a BAD COP ignition coil, this is the article for you. Also, all tests are ON CAR tests and done without a scan tool.

You can find a complete listing of GM vehicles that this info/tests apply to in the Applies To: box in the right column of this page.

Puedes encontrar este tutorial en Español aquí: Cómo Verificar las Bobinas de Encendido (GM 4.8L, 5.3L, 6.0L) (en:

Symptoms Of A BAD GM Coil-On-Plug (COP) Ignition Coil

The most common symptom will be a rough idle/misfire condition when the truck (or SUV) is idling or when accelerating. You may also experience this in combination with the following:

  1. Misfire codes that light up the check engine light (CEL) on your instrument cluster.
    1. P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308
  2. Engine misfire that DOES NOT light up the check engine light (CEL).
  3. Smell of unburned gasoline coming out of the tailpipe.
  4. Rotten egg smell coming out of the tailpipe. This is due to the unburned gasoline from the misfiring cylinder over loading the catalytic converter.
  5. Really BAD gas mileage.
  6. Lack of power as you accelerate the vehicle down the road.

What Tools Do I Need?

To test the COP ignition coils you do not need an automotive diagnostic scan tool (commonly known as a scanner or scan tool). You do need a few basic tools and these tools won't break the bank.

  1. An HEI spark tester
    1. This inexpensive spark tester is a MUST have tool to be able to correctly diagnose the Coil-on-Plug ignition coils on your GM vehicle with the info and tests in this article (don't have an HEI spark tester? Need to buy one? You can buy it here: OTC 6589 Electronic Ignition Spark Tester).
    Don't use a regular spark plug instead of a spark tester.
  2. Battery jump start cables.
  3. A digital multimeter.
    1. This multimeter must be able to read Hertz frequency (don't have a digital multimeter that can read Hertz frequency? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing).
  4. A helper.
    1. You'll need someone to help you crank the engine while you perform the tests in the engine compartment.
  5. A repair manual.
    1. For whatever remove and replace info you'll need that is not covered by this article.

Circuit Descriptions Of The C-O-P Ignition Coil Connector

Circuit Descriptions Of The C-O-P Ignition Coil Connector. How To Test The COP Coils (GM 4.8L, 5.3L, 6.0L, 8.1L)

All of the circuits can be tested without having to unplug the Coil-on-Plug ignition coil. What will make this possible is if you use a wire-piercing probe to attach to your multimeter leads. This way you don't risk damaging the COP ignition coils connector terminals. Any-hoo, here are the circuit descriptions:

  1. Circuit labeled 1:
    1. Power (12 V) Circuit.
  2. Circuit labeled 2:
    1. IC Signal (Ignition Control) Circuit. Also known as the Triggering Signal.
  3. Circuit labeled 3:
    1. Low Reference Circuit. Also known as the Ground provided by the PCM internally.
  4. Circuit labeled 4:
    1. Chassis Ground.

You don't have to worry about the color of the wires as long as you're able to identify the circuit using the photos in each test step.

Do's And Don'ts And Precautions

The tests that you're about to learn/do in this article are very easy and simple to do. But you still have to be on your toes and remain alert. Use common sense and take all necessary safety precautions. Here are some more suggestions:

  1. Do not use a regular spark plug instead of a spark tester to test for spark.
  2. Do not remove the spark plug wire from the spark plug or the ignition coil while the engine is cranking to test for spark.
  3. Start your diagnostic from TEST 1, do not skip around from test to test unless instructed to do so by the TEST you are currently on.
  4. Do not use a test light where an LED light is called for.
  5. Once again, use the recommended/indicated tools for all of your tests.
  6. Some folks love to waste time and money... if you're one of them, disregard everything in this section.