TEST 2: Verifying The Start Signal
Since the starter motor is not engaging the engine, when you turn the key to crank and try to start it, we now need to verify the presence of the Start signal.
The Start signal is the voltage signal that activates the starter motor and is received on the starter motor solenoid's S terminal.
This test simply involves connecting our multimeter to the S terminal wire and turning the key to crank and start the engine.
If the Start signal is present, then your multimeter should read 10 to 12 Volts DC. If it isn't, then it'll just read 0 Volts DC.
Let's get going:
- 1
Connect the red multimeter test lead to the S terminal of the starter motor.
- 2
Attach the black multimeter test lead to a clean and rust-free spot on the engine or on the vehicle frame.
I recommend that you use a battery jump start cable to Ground the black multimeter test lead directly to the battery negative (-) terminal. - 3
Have your helper crank the engine from inside your Chevy/GMC pick-up or SUV.
The engine won't turn over, but the idea is to verify that the starter motor's internal solenoid is getting the 12 Volt start signal from the ignition switch (or not). - 4
Your multimeter is going to register one of two results: Either 10 - 12 Volts DC or no voltage at all.
Let's examine your test result:
CASE 1: The multimeter registered 10 to 12 Volts. This test result lets you know the starter's internal solenoid is receiving the start signal.
This means that we can forget about the safety neutral switch and the ignition switch being bad. OK, now the next test is to do a very easy and simple voltage drop test. Go to: TEST 3: Voltage Drop Testing The Battery (+) Cable.
CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This result exonerates the starter motor. Your starter motor is not the cause of the no-crank condition.
Here's the reason why: Without this 10 to 12 Volt crank signal, the starter motor will not engage and crank your pick-up or SUV's engine. Now, although it's beyond the scope of this article to test the neutral safety switch or the ignition switch, you have eliminated the starter motor and this means saving money by not buying a part your vehicle does not need.
TEST 3: Voltage Drop Testing The Battery (+) Cable
In some cases the starter motor won't crank the engine even though the battery is fully charged, the engine isn't locked up (like when it throws a rod), the starter solenoid is receiving the Start signal, and the starter motor bench-tested good.
In these cases what is usually causing the problem is hidden corrosion in the battery cable that connects the starter to the battery.
The best way to confirm this is to do a voltage drop test. Yup, this test will help us to make sure that all of the battery's current is reaching the starter motor.
This is a very easy test to do and all you need is a multimeter. These are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 2
Attach the red multimeter test lead to the center of the positive battery terminal.
If the positive battery post isn't clean, clean a spot right on the top of it. It's important that the multimeter lead make contact right in the center of the positive battery post. - 3
With the black multimeter test lead, touch the center of the starter stud to which the big battery cable attaches to. You'll maintain the black multimeter test lead in this position throughout the next step.
- 4
Have your helper crank the engine even though the starter motor isn't cranking the engine.
This is important, since a voltage drop test has to be done while the component in question is working (or trying to work). - 5
If all is good (no voltage drop), your multimeter will register 0 Volts (.5 Volts is still 0 Volts).
If there's a voltage drop (which is bad), your multimeter will register voltage (usually above 7 Volts DC.)
Let's take a look at what your results mean:
CASE 1: Your multimeter registered 0 Volts (no voltage drop). This result indicates that the starter motor is receiving all of the battery voltage and amperage it needs to crank the vehicle.
You can conclude the starter motor, on your Chevy/GMC pick-up or SUV, is defective if you have:
- Confirmed that the starter motor doesn't work when you apply power to the S terminal wire of the starter motor (TEST 1).
- Confirmed that the starter motor is receiving the crank signal (TEST 2).
- In this test step, you have confirmed that no voltage drop exists on the battery positive cable.
Replacing the starter motor should solve your no-crank condition.
I'm going to make two more recommendations to you:
- Before removing the starter motor, manually turn the engine using a 1/2 ratchet and the appropriate socket. This is to make sure that the engine or the A/C compressor have not locked up and causing the no-crank condition.
- Bench test the starter motor after removing it. This is a super easy test to do and this tutorial will help: Bench Testing The Starter Motor.
CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and that the battery's full power is not reaching the starter motor.
The good news is that this can easily be corrected, since a voltage drop is always caused by some sort of corrosion issue on the battery positive cable or terminals or the battery positive post.
The solution is to thoroughly clean the battery positive post and the battery positive (+) terminal (both the end that attaches to the battery positive post and the end the connects to the starter motor's battery (+) cable stud.
After cleaning, try cranking the engine. If it cranks and starts, no further testing is required.
More GM 4.3L, 5.0L, And 5.7L Tutorials
You can find a complete list of GM 4.3L, 5.0L, and 5.7L tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04).
- How To Clean The GM Mass Air Flow (MAF) Sensor.
- How To Test The Throttle Position Sensor (GM 4.3L, 5.0L, 5.7L).
- How To Test The GM Ignition Control Module (1995-2005).
If this info saved the day, buy me a beer!
