TEST 1: Making Sure The Power Transistor Is Getting Ground

Making Sure The Power Transistor Is Getting Ground. How To Test The Power Transistor 1992, 1993, 1994 Nissan D21 Pickup

The first thing we'll do, to get this show on the road is to make sure the power transistor is getting Ground.

Chassis Ground is fed to the power transistor by the black (BLK) wire of the power transistor's 3-wire connector.

Alright, let's get going:

  1. 1

    Disconnect the power transistor from its electrical connector.

  2. 2

    Connect the black multimeter test lead to the BLK wire of the power transistor's electrical connector. This is the middle wire of the connector.

  3. 3

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

  4. 4

    Your multimeter should read 10 to 12 Volts DC if the power transistor is getting Ground.

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

CASE 1: The power transistor is getting Ground. This is the correct and expected test result.

The next step is to make sure the power transistor is getting a triggering signal from the fuel injection computer. For this step, go to: TEST 2: Making Sure The Power Transistor Is Being Triggered.

CASE 2: The power transistor IS NOT getting Ground. This tells you that the power transistor is not working due to a lack of Ground.

Your next step is to repair and restore Ground to the connector. Once the Ground circuit is restored, the power transistor should function again.

TEST 2: Making Sure The Power Transistor Is Being Triggered

Making Sure The Power Transistor Is Being Triggered. How To Test The Power Transistor 1992, 1993, 1994 Nissan D21 Pickup

Your 2.4L Nissan D21's fuel injection computer (PCM) is the one that controls the power transistor.

The fuel injection computer sends a triggering signal, to the power transistor, across the white (WHT) wire of the 3-wire connector.

To test the power transistor triggering signal, we'll need to use a multimeter that can read Hertz frequency.

OK, these are the test steps:

  1. 1

    Place your multimeter in Hertz mode. Leave the power transistor connected to its connector.

  2. 2

    Connect the red multimeter test lead to the WHT wire of the connector.

    You'll need to use a back probe or a wire piercing probe to get to the signal inside the wire.

  3. 3

    Ground the black multimeter test lead directly on the battery negative (-) terminal.

  4. 4

    Have your helper crank the engine while you observe the multimeter's reading.

  5. 5

    Your multimeter should read 6 to 8 Hertz (Hz) if the power transistor is being triggered by your Nissan D21's fuel injection computer.

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

CASE 1: The power transistor is getting a triggering signal. This is the correct and expected test result.

This test result tells you that the power transistor is defective (and needs to be replaced) only if you have:

  1. Made sure the ignition coil is not sparking and not getting a control signal from the power transistor.
  2. Made sure the power transistor has good Ground (TEST 1).
  3. Made sure the power transistor is getting the triggering signal from the fuel injection computer (TEST 2).

CASE 2: The power transistor IS NOT getting a triggering signal. This tells you that the power transistor is not activating the ignition coil due to a lack of its triggering signal.

This usually means that the crank angle sensor inside the distributor is defective. Although it's beyond the scope of this tutorial to test the crank angle sensor, you have confirmed that the power transistor is not defective since it won't function without its triggering signal.

Testing the crank angle sensor is not hard and this tutorial will help you test it: How To Test The Crank Angle Sensor (1990-1996 2.4L Nissan Pickup).

Where To Buy The Power Transistor (Ignition Control Module)

Yup, the Nissan D21 power transistor can get 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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