TEST 5: Testing The Ignition Coil's Switching Signal
As you may already know, the power transistor is the one responsible in activating the ignition coil to start sparking away on your Nissan SUV (or Pick Up or Mini-Van).
It does this by creating and sending a Switching Signal (activation signal) to the ignition coil. This signal can be easily tested with an LED Light. In this test step you're gonna' verify if indeed this signal is being supplied to the ignition coil.
NOTE 1: The distributor must remain connected to its 2 connectors. You'll need to use a back probe or a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe Review (Power Probe PWPPPPP01).
NOTE 2: The photo above is of the Nissan Pathfinder's 6-wire connector. If your vehicle is not a Pathfinder (or QX-4), the colors of the wires will be different. This is no cause for concern because the circuit descriptions are the same.
Alright, let's get started:
This test must be done with both of your Nissan distributor's connectors connected to the distributor.
Connect the black lead of the LED light to the wire (circuit) identified with the number 8 in the photo. This should be the blue wire of the two wire distributor connector (the distributor has one 6 wire connector and a 2 wire connector).
Connect RED lead of LED to the battery (+) positive terminal. It's important that it be connected at the battery positive terminal.
Have an assistant crank the engine.
The LED Light should blink on and off the whole time the engine is being cranked.
NOTE: Don't worry about what the LED Light does before or after your helper starts cranking the engine. The only results you're interested in interpreting are the results obtained with the engine cranking.
Let's examine your test result:
CASE 1: The LED flashed On and Off. This is the correct test result.
With this test result you can conclude that the ignition coil is bad and needs to be replaced. This also means that the power transistor is good.
Here's why: If the ignition coil is getting 10 to 12 Volts (TEST 4) and it's getting an activation signal (TEST 5), then it has to spark. Since your test result confirms that it isn't sparking, then you can conclude that it's defective.
Replacing the ignition coil will solve your no-spark/no-start condition. The only thing that sucks is that at the time of this writing, you cannot buy the ignition coil separately since you have to buy the whole distributor.
CASE 2: The LED DID NOT flash ON and OFF. Without the activation signal, the ignition coil will not spark.
Re-check all of your connections and repeat the test. If the LED light does not flash on and off then the next step is to test the power transistor (ignition control module). For this test go to: TEST 6: The Power Transistor's Ground Circuit.
TEST 6: The Power Transistor's Ground Circuit
For the power transistor to activate the ignition coil, it has to have a good path to Ground and in this test will help you to verify that it does.
To check for ground, we're gonna' do a simple multimeter voltage test on the wire labeled with the number 2 in the photo above.
NOTE: The photo above is of the Nissan Pathfinder's 6-wire connector. If your vehicle is not a Pathfinder (or QX-4), the colors of the wires will be different. This is no cause for concern because the circuit descriptions are the same.
These are the test steps:
Select Volts DC mode on your multimeter.
With the black multimeter test lead probe the wire identified with the number 2 in the photo of the 6 wire distributor connector.
Connect the red multimeter test lead to the battery (+) positive terminal.
You should see 12 Volts on the multimeter without having to turn the Key to ON. Do you have 12 Volts?
Let's analyze your test result:
CASE 1: Your multimeter displayed 12 Volts. This is the correct test result and lets you know that the power transistor has a good path to Ground.
The next step is to check that the power transistor is receiving a Triggering signal (activation signal) from the fuel injection computer. For this test go to: TEST 7: Testing The Triggering Signal From The PCM.
CASE 2: Your multimeter DID NOT display 12 Volts. Without Ground the power transistor will not activate the ignition coil.
Your next step is to resolve this Ground issue. Once Ground is restored, the power transistor will activate the ignition coil.