TEST 4: Making Sure The Power Transistor Is Activating The Ignition Coil

Making Sure The Power Transistor Is Activating The Ignition Coil. How To Test The Ignition Coil 1992-1994 Nissan D21 Pickup

In this last test, we're gonna' make sure that your Nissan D21's power transistor is activating the ignition coil.

This is a very easy and simple test that we'll accomplish using an LED light with a built in resistor.

To see an example of the LED light that you need to use, and the one that I use to test the ignition coil control signal, go here: The LED Light Test Tool and How To Make One.

If this test confirms that the power transistor is activating the ignition coil, then we can conclude that the ignition coil is defective (when taking into account all of your previous test results).

NOTE: LEDs are polarity specific and so their wires will be black and red. This also means that you'll need to pay close attention to where the instructions are telling you to connect the black or red LED wires.

Here are the test steps:

  1. 1

    Disconnect the ignition coil from its connector.

    IMPORTANT: This test is done on the ignition coil's engine wiring harness connector. This connector has female metal terminals and you should avoid inserting any type of test lead into them. Use a back probe or wire piercing probe.

  2. 2

    Connect red LED wire to the BLK/WHT wire of the ignition coil's wiring harness connector. This is the power circuit of the ignition coil.

    IMPORTANT: Do not insert a thick male spade terminal or wire into the female terminal of the connector, or you'll damage the terminal.

  3. 3

    Connect black LED wire to the BLU wire of the ignition coil's wiring harness connector. This is the activation signal circuit of the ignition coil.

    IMPORTANT: Do not insert a thick male spade terminal or wire into the female terminal of the connector, or you'll damage the terminal.

  4. 4

    Have your helper crank the engine after the LED light is set up.

  5. 5

    The LED light should flash ON and OFF as the engine turns if the ignition coil control signal is present.

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

CASE 1: The LED light flashed ON and OFF as the engine was cranked. This is the correct and expected test result and confirms that your Nissan D21's power transistor (ignition control module) is activating the ignition coil.

You can now conclude that the ignition coil is defective and needs to be replace if you have:

  1. Confirmed a lack of spark at all 4 cylinders.
  2. Confirmed that the ignition coil's high tension wire is not sparking (TEST 1).
  3. Confirmed no spark directly on the ignition coil tower (TEST 2).
  4. Confirmed the ignition coil is getting 12 Volts (TEST 3).
  5. Confirmed the ignition coil is getting an activation signal from the power transistor (TEST 4).

CASE 2: The LED light DID NOT flash ON and OFF as the engine was cranked. This tells you that the power transistor (ignition control module) is not sending an ignition coil control signal.

Although it's beyond the scope of this tutorial to test the power transistor, you have eliminated you Nissan D21's ignition coil as defective (since without its activation signal, it won't spark).

If you need help testing the power transistor, check out this tutorial: How To Test The Power Transistor 1992-1994 Nissan D21 Pickup.

Where To Buy The Ignition Coil

Yup, this bad boy isn't expensive. Check out the following links and comparison shop:

More 2.4L Nissan Tutorials

You can find a complete list of tutorials here: Nissan 2.4L Index Of Articles.

Here's a sample of the tutorials you'll find there:

  1. Mass Air Flow (MAF) Sensor Test 2.4L Nissan D21 Hard Body (1990-1995).
  2. How To Test Engine Compression (Nissan 2.4L) (at: troubleshootmyvehicle.com).
  3. How To Test The Throttle Position Sensor (2.4L Pick Up, Frontier, Xterra).
  4. Oxygen Sensor Heater Test -P0135 (1996-1997 2.4L Pick Up).
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