How To Test The Power Transistor 2.4L Nissan Frontier, Xterra (1998-2004)

TEST 2: Verifying The Power Transistor's Triggering Signal

In this test step, you're gonna' check that the power transistor (igniter) is getting the Triggering signal from the fuel injection computer or not.

This Triggering signal can be very easily and accurately tested using a simple automotive LED light. If you need to see what this LED light looks like, you can see it here: The LED Light Test Tool And How To Make One.

OK, now for this test, this is what you need to do:

1. 1

   Locate the wire labeled with the number 1 (see photo above).

2. 2

   OK, locate the wire that the orange arrow is pointing to (on your distributor) connect the red lead of the LED to this wire using an appropriate tool (like a wire piercing probe).

3. 3

   Next, connect the black lead of the LED light to the battery negative (-) terminal.

4. 4

   When you have everything set up, have your helper crank the engine as you observe the LED light.

5. 5

   The LED light should blink ON and OFF the whole time your helper is cranking the engine.

Let's take a look at what your test result means:

CASE 1: The LED light blinked ON and OFF. This is the normal and expected test result and tells you that the fuel injection computer is triggering the power transistor. The next step is to check that the power transistor is producing a switching signal for the ignition coil, go to: TEST 3: Verifying The Ignition Coil's Switching Signal.

CASE 2: The LED light DID NOT blink ON and OFF. This result eliminates the power transistor as bad. Without this Triggering signal from the fuel injection computer, the power transistor will not work.

Although it's beyond the scope of this article to troubleshoot the cause of this missing Triggering signal, you have at least eliminated the power transistor (igniter) as the cause of the no-start problem.

The next step, is to test the cam sensor, since the camshaft position sensor is the one responsible for the creation of the Triggering signal. You can find the test here: 2.4L Frontier, XTerra Cam Sensor Test (98-04).

TEST 3: Verifying The Ignition Coil's Switching Signal

As you're already aware, the purpose of the igniter is to activate the ignition coil.

How does the igniter activate the ignition coil to spark? By interrupting the coil's power supply (which in tech speak is called the Primary Current).

To explain this another way, the igniter switches the Primary Current ON and OFF.

So, in this test step, you're gonna' check to see if the power transistor is creating this activation signal (referred to as the switching signal) using the same LED light that you used in TEST 2.

OK, now for this test, this is what you need to do:

1. 1

   Remove the plastic dust cap that is underneath the distributor rotor.
   
   To be a little more specific: this is the plastic protective cap that protects all of the wires and the igniter inside the distributor and that can be removed by first removing the distributor rotor and then the two little screws that hold it in place.

2. 2

   It's not necessary to remove the distributor from the car to remove this dust cap. Once you've removed the dust cap, your distributor should look like the one in the photos.

3. 3

   Connect the black lead of the LED to the wire labeled with the orange arrow, using an appropriate tool (like a wire piercing probe).

4. 4

   Next, connect the red lead of the LED light to the battery positive (+) terminal.

5. 5

   When you have everything set up, have your helper crank the engine as you observe the LED light.

6. 6

   The LED light should blink ON and OFF the whole time your helper is cranking the engine.

Let's interpret your test result:

CASE 1: The LED light DID NOT blink ON and OFF. Then this confirms that the igniter is bad and needs to be replaced, since it's unable to create the switching signal to activate the ignition coil. Replace the power transistor.

Now what sucks about replacing the power transistor is that at the time of this writing, the only way you can replace it is by buying the whole distributor.

To go into more specific details, you can conclude the power transistor is bad and needs to be replaced if you have:

• The power transistor is getting power, which you confirmed in TEST 1.
• The power transistor is getting the Triggering signal from the fuel injection computer, which you have confirmed in TEST 2.

CASE 2: The LED light blinked ON and OFF. This result tells you that the power transistor is working and creating the ignition coil's switching signal.

This result also confirms that the power transistor is not the cause of your 'no-start no-spark' condition on your 2.4L Nissan Frontier (or Xterra).