IGNITION COIL TEST 4: Checking For The Presence Of The Activation Signal
In the previous test you confirmed that the ignition coil is being supplied with power (12 Volts DC).
Now, you need to see if the ignition coil is getting an activation signal, called the switching signal, from the PCM.
This switching signal from the PCM is what actually activates the ignition coil to fire off spark.
This test is accomplished using a 12 Volt test light and is done while cranking the engine on your 3.9L, 5.2L, or 5.9L Dodge pick up (or van or SUV).
Alright, this is what you'll need to do:
- 1
Reconnect the high tension wire to the ignition coil and the distributor cap, if you haven't done so.
- 2
Connect the alligator clip (of the 12 V test light) to the positive (+) battery terminal.
The ignition coil can be connected to its electrical connector or not. - 3
Probe the wire labeled with the number 1 (see photo above) with the metallic tip of the 12 Volt test light.
- 4
When ready, have your helper crank the engine while you observe and hold the test light in place.
- 5
Your 12 Volt test light should flash ON and OFF the whole time the engine is cranking.
Let's take a look at what your results mean:
CASE 1: The test light flashed ON and OFF. This is the correct test result and means that the Powertrain Control Module (fuel injection computer) is activating the ignition coil.
You can conclude that the ignition coil is bad and needs to be replaced if you have:
- Confirmed that the ignition coil's high tension wire is not sparking (TEST 1).
- Confirmed that the ignition coil's tower is not sparking (TEST 2).
- Confirmed that the ignition coil is getting 10 to 12 Volts (TEST 3).
- Confirmed in this test step the ignition coil is getting an activation signal.
If you'd like to save a few bucks on the ignition coil, take a look at the section: Where To Buy The Ignition Coil And Save.
CASE 2: The test light DID NOT flash ON and OFF. This test result exonerates the ignition coil, since without this switching signal, it won't spark.
The most likely causes of this missing switching signal are: a bad crank sensor, an open or a short in the wiring between the PCM and the ignition coil's connector, or the PCM (Powertrain Control Module = fuel injection computer) is bad (although this is a rare thing).
Altho' it's beyond the scope of this article to test the wiring or the PCM, you have at least eliminated the ignition coil as bad.
To test the crank sensor, I suggest taking a look at the following tutorials:
- How To Test The Crank Sensor (1994-1996 3.9L, 5.2L, 5.9L Chrysler).
- How To Test The Crank Sensor (1997-2001 3.9L, 5.2L, 5.9L Chrysler).
More Dodge 3.9L, 5.2L, 5.9L Tutorials
I've written several more tutorials that may be of interest to you. These are specific Dodge pick up, van or SUV tutorials that you can find at: Dodge 3.9L, 5.2L, 5.9L Index Of Test Articles.
- How To Test A No Start Condition (Dodge 3.9L, 5.2L, 5.9L).
- How To Test The Crank Sensor (1994-1996 3.9L, 5.2L, 5.9L Chrysler).
- How Can I Tell If My Automatic Transmission Needs An Overhaul?
- How To Test The MAP Sensor (P0107, P0108) (Dodge 3.9L, 5.2L, 5.9L).
- How To Diagnose Misfire Codes (Dodge 3.9L, 5.2L, 5.9L).
If this info saved the day, buy me a beer!
