How To Test The Ignition Coil Packs (GM 3.1L, 3.4L)

TEST 5: Verifying The Ignition Coil's Switching Signal

This is the final test step and a continuation of TEST 4. Depending on the results you'll obtain, you'll be able to say that the ignition coil or the ignition control module (ICM) is bad.

For this test, you can not use a test light. You'll need an LED light for this test. Take a look at this LED light tool here: The LED Light Test Tool And How To Make One. Also, this test is performed with the engine cranking.

CAUTION: This test has to be done with the engine cranking. Be careful and take any necessary safety precautions.

OK, with the ignition coil that isn't sparking (from its two towers) still off from the previous step (TEST 4)

1. 1

   Place the red lead of the LED on the male spade terminal labeled with the + symbol.

2. 2

   Place the black lead of the LED on the male spade terminal labeled Signal.
   
   This is the terminal that provides the Switching signal.

3. 3

   Have your helper crank the engine while you observe the LED light.
   
   NOTE: Whether the LED light comes ON or is OFF before and after you crank the engine does not matter. The only flashing (or lack of) that you need to worry about, is during the cranking part.

4. 4

   You should see the LED light flashing ON and OFF while the engine is cranking.

Let's take a look at what your test results mean:

CASE 1: The LED flashed ON and OFF. This result confirms that the ignition module is good and that it's providing an activation signal to the coil that is not firing off spark from its two towers.

This test result also tells you that the ignition coil is bad and needs replacement if you have:

• Confirmed that the two spark plug wires that connect to the ignition coil are not sparking (TEST 2).
• Confirmed that the ignition coil's two towers are not sparking (TEST 3).
• Confirmed that the ignition control module is feeding power to the ignition coil (TEST 4).
• In this test section, confirmed that the ignition control module is providing an activation signal.

CASE 2: The LED DID NOT flash ON and OFF. This test result confirms that the ignition control module is not providing the ignition coil an activation signal.

You can conclude that the ignition control module is bad and needs replacement if you have:

• Confirmed that the two spark plug wires that connect to the ignition coil are not sparking (TEST 2).
• Confirmed that the ignition coil's two towers are not sparking (TEST 3).
• Confirmed that the ignition control module is feeding power to the ignition coil (TEST 4).
• In this test section, confirmed that the ignition control module IS NOT providing an activation signal.

More GM 3.1L, 3.4L V6 Tutorials

If this tutorial was helpful, there's plenty more, and you can find them in the following new indexes:

• GM 3.1L Index of Articles (Chevrolet and Pontiac).
• GM 3.4L Index of Articles (Chevrolet and Pontiac).
• GM 3.1L, 3.4L Index of Articles (old section).

New 3.1L and 3.4L V6 Buick and Oldsmobile diagnostic tutorials can be found here:

• GM 3.1L Index of Articles (Buick and Oldsmobile) (at: troubleshootmyvehicle.com).
• GM 3.4L Index of Articles (Buick and Oldsmobile) (at: troubleshootmyvehicle.com).
• GM 3.1L, 3.4L Index of Articles (old section) (at: troubleshootmyvehicle.com).