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

TEST 5: Testing The Low Reference Circuit

In this test section, we're gonna' test the 2nd Ground the ignition coil receives. This Ground is supplied by the fuel injection computer (PCM).

Testing the Ground circuit (known in tech speak as the Low Reference Circuit), that the PCM provides, can be accomplished with the Coil-On-Plug (COP) Coil connected or disconnected to its connectors.

IMPORTANT: Since this Ground is provided by the PCM, you need to be very careful not to short this circuit to 12 Volts or you'll fry the PCM.

These are the test steps:

1. 1

   Disconnect the ignition coil from its connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   Probe the circuit labeled with the number 3 (in the photo above) with the black multimeter test lead.
   
   You can either back probe the connector, or use a wire piercing probe on the wire.
   
   If you probe the front of the connector, be careful not to damage the female terminal.

4. 4

   Connect the red multimeter test lead probe the battery positive (+) terminal.

5. 5

   Have your helper turn the key to the ON position.

6. 6

   You should see 10 to 12 Volts on your multimeter.

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

CASE 1: The multimeter registered 10 to 12 Volts (or the test light lit up). This is the correct test result and it lets you know that the PCM is providing the 2nd Ground.

The next step is to make sure that the PCM is activating the ignition coil, go to: TEST 6: Testing The IC Signal (Triggering Signal).

CASE 2: The multimeter DID NOT register 10 to 12 Volts (or the test light DID NOT light up). Then the Low Reference Circuit has a problem.

Recheck all of your multimeter connections and retest. If still the multimeter does NOT register the specified voltage, then this result eliminates the COP ignition coil as the source of the misfire condition. You must find out the causing this missing 2nd Ground.

TEST 6: Testing The IC Signal (Triggering Signal)

OK, so far all your tests have confirmed that three out of four circuits DO HAVE the correct signal coursing thru' them.

The next step is to verify that that Coil-On-Plug (COP) ignition coil is receiving the Triggering signal from the PCM (Powertrain Control Module = Fuel Injection Computer).

This test is done with a multimeter that can read Hertz Frequency (don't have one? No problem, go to: TEST 7: Testing The Trigger Signal Without A Multimeter).

Testing for the Triggering Signal should be done with the ignition coil connected to its connector.

The method I recommend to use is with them connected to their connectors and with a wire-piercing probe. You can see an example of this tool here: Wire-Piercing Probe.

Let's get testing:

1. 1

   Place your multimeter in Hertz (Hz) mode and keep the ignition coil connected to its connector.

2. 2

   Probe the circuit labeled with the number 2 (see photo above) with the black multimeter test lead using an appropriate tool.

3. 3

   Connect the red multimeter test lead probe the battery positive (+) terminal.

4. 4

   Have your helper crank and start the engine as you observe the multimeter.

5. 5

   You should see fluctuating values of 5 to 8 Hertz as the engine starts and runs on your multimeter.
   
   NOTE: If you're unsure of your Hertz reading, don't worry. Test the adjacent (or any other COP coil) for its Triggering signal and compare that signal to this one. Both signals should behave the same.

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

CASE 1: The multimeter registered 5 to 8 Hertz (Hz) as the engine cranked and started. This is the correct test result and it tells you that the Triggering Signal is present.

This result, also, indicates that the Coil-On-Plug ignition coil on your GM vehicle is bad and needs to be replaced only if:

• The coil is not firing spark in TEST 1 and 2.
• It's getting power (10 to 12 Volts DC) in TEST 3.
• It's getting chassis Ground in TEST 4.
• It's getting PCM Ground in TEST 5.
• It's getting the triggering signal from the PCM (TEST 6).

CASE 2: The multimeter DID NOT register 5 to 8 Hertz (Hz) as the engine cranked and started. Re-check all of your connections and repeat the test again.

If still no Hertz readings, then this result eliminates the ignition coil as the source of the no-spark condition/misfire, since without the Triggering signal the ignition coil will not work.

This lack of Signal indicates one of two things: 1) An open-circuit problem in the circuit between the COP coil and the PCM or 2) a bad PCM, altho' a bad PCM is rare, but it happens.

TEST 7: Testing The Trigger Signal Without A Multimeter

You've heard the saying that 'there's more than one way to skin a cat' (I love cats, please no hate mail over this), well in this test step I'll show you how to verify that the Triggering signal is indeed present on the Coil-On-Plug ignition coil that didn't fire off spark without having to use a multimeter.

These are the test steps:

1. 1

   Disconnect and remove the Coil-On-Plug (COP) ignition coil that didn't fire off spark in TEST 1 and 2.

2. 2

   Remove one of the adjacent COP ignition coils (that you know for a fact that it's firing off spark) next to the one you just removed.

3. 3

   Connect the COP ignition coil (that sparks) to your HEI spark tester
   
   Now connect (this same coil that sparks) to the connector of the ignition coil that did not spark.

4. 4

   Now, have your trusty assistant crank the engine and notice if the HEI spark tester sparks.
   
   NOTE: Be careful, the engine will probably start.

5. 5

   If the Triggering Signal is present, then this COP ignition coil will fire spark connected to this connector. If the Triggering Signal is missing for any reason, it won't spark.

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

CASE 1: You got spark. Then this test result tells you that the Triggering Signal is present.

This result also tells you that the Coil-On-Plug ignition coil on your GM vehicle is bad and needs to be replaced only if:

• The coil is not firing spark in TEST 1 and 2.
• It's getting power (12 Volts DC) in TEST 3.
• It's getting chassis Ground in TEST 4.
• It's getting PCM Ground in TEST 5.
• It's getting the triggering signal from the PCM (TEST 7).

CASE 2: You got NO spark. Re-check all of your connections and repeat the test again. If still no spark, then this results eliminates the ignition coil as the source of the no-spark condition/misfire, since without the Triggering Signal the COP ignition coil will not work.