How To Test The Starter Motor (GM 4.3L, 5.0L, 5.7L)

STARTER TEST 2: Verifying The START Signal

The starter motor on your GM pick up, van or mini-van comes alive only when you turn the ignition key to the Start Position. Now, to get a little more technical, but using plain English, the ignition switch sends 12 Volts to the starter motor solenoid's S terminal. But before it reaches the starter motor solenoid's S terminal, these 12 Volts have to pass thru' the neutral safety switch (whether your vehicle has an automatic or manual transmission).

So, in this test step, we're gonna' check that the starter motor is receiving this Start signal. This test can easily be accomplish with a multimeter or a 12 Volt automotive test light (although I prefer the multimeter).

OK, this is what you'll need to do:

1. 1

   Lift the front of your vehicle and place it on jack stands (if it isn't already).

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter test lead to the battery negative (-) terminal or a clean and rust-free spot on the engine or on the vehicle frame.
   
   Now, if I where in your shoes (doing this test), I would use a battery jump start cable to connect the black multimeter test lead directly to the battery negative (-) terminal. Why? Well, it might be near impossible to find a clean rust-free spot of metal underneath your vehicle.

4. 4

   Connect the red multimeter test lead to the S terminal on the solenoid and hold it there for the duration of this test.
   
   There's a good chance that you may not be able to get the S terminal because of the reduced space around the starter motor, if this is the case, you'll need to use a wire piercing probe to connect the red multimeter lead to the S terminal wire.
   
   If you're scratching you head wondering what/where is the S terminal on the starter motor: The S terminal is the smaller of the three studs on the starter solenoid. This is where the wire (circuit) that supplies the Start (Crank) signal from the ignition switch (in the photo above, the orange arrow points to this S terminal) connects to at the starter motor solenoid.

5. 5

   Once you have everything set up, have your helper turn the key to crank the engine.
   
   NOTE: Now, the engine is not gonna' turn over, of course, but if you don't do this, you won't be able to confirm the presence of the Crank (START) signal from the ignition switch.

6. 6

   The multimeter should register between 10 to 12 Volts DC as you helper turns the key to the START position.

Let's take a look at your test result:

CASE 1: Your multimeter registered 10 to 12 Volts. This is good, since it let's you know that the starter motor is getting a crank signal from the ignition switch.

This test result also confirms that the neutral safety switch is good and doing its job. Now, in the majority of the cases, you could stop testing here, replace the starter motor and be done. But, I suggest one more test so that you can be absolutely sure there isn't another issue to deal with.

The next test would be to voltage drop test the battery positive cable that connects to the starter motor solenoid. This is a very easy and simple test to do, and in STARTER test 2 I'll show you how to do it. Go to: TEST 3: Voltage Drop Testing The BAT + Cable.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This result lets you know that the reason the starter motor is not cranking up the engine is through a lack of a Crank (Start) signal.

Here's why: without this crank signal, the starter motor will not crank the engine. This signal could be missing because either the neutral safety switch is bad or a bad ignition switch. testing these two components is beyond the scope of this article but you have now eliminated the starter motor as bad.

STARTER TEST 3: Voltage Drop Testing The BAT + Cable

So far in your testing, you have verified that the battery is fully charged and in STARTER TEST 2 you confirmed that the starter motor is being supplied with the START signal (when your helper turned the key to crank the engine).

The next step is to make sure that the battery positive (+) cable (BAT +) that attaches to the starter motor's solenoid is supplying full battery voltage and amperage to the starter motor, because if it isn't (usually due to hidden corrosion somewhere on the cable), the starter motor won't be able to crank the engine.

We can easily accomplish this by doing a simple multimeter voltage drop test on the BAT + cable, which will help us determine if there's any significant corrosion causing resistance in the cable.

This is a very simple test to perform, as you're essentially just measuring the difference in voltage between two points in the BAT + cable (with your multimeter in Volts DC mode) while current is flowing.

If your multimeter registers a significant voltage drop (5 Volts or more), there's corrosion causing resistance in the BAT + cable. This corrosion can impede the flow of battery current and affect the performance of the starter motor.

Let's get started:

1. 1

   Place your multimeter still in Volts DC mode.

2. 2

   Attach the red multimeter test lead to the center of the positive (+) battery post.
   
   NOTE: The spot on the battery positive (+) post has to be clean and rust-free.
   
   You may need two helpers for this test step, since someone will have to hold the red multimeter test lead onto the battery positive (+) terminal bolt and someone else inside the vehicle (to crank it when everything is set up).

3. 3

   With the black multimeter test lead, probe the BAT + stud on the starter solenoid.
   
   Maintain the black multimeter test lead in this position throughout the next step.
   
   NOTE: The BAT + stud on the starter motor solenoid is where the battery positive (+) cable connects to. The other end of this cable attaches to the battery positive (+) post.

4. 4

   Have your helper crank the engine when everything is set up.
   
   NOTE: Although the starter motor won't crank the engine, your helper has to turn the ignition switch to the START position for the voltage drop test to work.

5. 5

   The multimeter should register 0.5 Volts or less (0.5 V is really 0 Volts).
   
   If there's a problem in this circuit, your multimeter will register some voltage, usually 5 Volts or above (which would indicate a voltage drop).

OK, now that the testing part is done, let's take a look at what your results mean:

CASE 1: Your multimeter indicated NO voltage drop (which is 0.5 Volts or less). This result indicates that the starter motor is receiving all of the battery voltage and amperage it needs to crank the vehicle.

This result also confirms that the starter motor is bad and needs to be replaced, and this is why: The result of STARTER test 1 confirmed that the ignition switch and the neutral safety switch are good and that the starter is getting the Crank signal. The test you just got done doing, confirms that the starter is getting all of the power it would need to crank the engine. So, both of these test results confirm you have a bad starter on your hands.

Now, before you remove the starter motor, do two more things:

1.) Turn the engine manually (using a 1/2 ratchet and the appropriate socket). This will verify that the engine is not mechanically locked up.

2.) Bench test the starter motor. You can find the step-by-step instructions here: How To Bench Test A Starter Motor (Step By Step).

CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and this a voltage drop is not a good thing to have in this circuit.

The solution is to simply disconnect the battery positive (+) cable from the battery and thoroughly clean it. Also, the end of this very same cable, that's attached to the starter motor solenoid, should be disconnected, inspected and cleaned.

Cleaning the end that attaches to the starter motor solenoid should be done with a small piece of sand paper. Once both ends of the battery positive cable are clean, reconnect everything and try cranking the car. If the voltage drop was the cause of the no-crank condition, then your vehicle will now crank and start.

Related Test Articles

There are several more GM 4.3L, 5.0L and 5.7L specific ‘How to test’ articles that I've written for your troubleshooting and diagnostic benefit. The articles that are here (in this web site) you can find them here:

• GM 4.3L, 5.0L, 5.7L Index Of Articles.

If you need to test the ignition system (like the ignition module, ignition coil, distributor cap, spark plug wires), you can find the step-by-step tests in the following two test articles (found at easyautodiagnostics.com).

• How to test a Misfire / No-Spark No-Start Condition GM 4.3L, 5.0L, 5.7L Distributor Ignition System (1996-2004).
  • This article will help you to find the cause of a misfire or 'no-spark no-start' condition on your GM car, Pick Up, mini-van, van or SUV equipped with a 4.3L, or 5.0L, or 5.7L engine. The testing is explained step by step, making the whole diagnostic and troubleshooting as pain free as possible.
• How to test GM Ignition Control Module 4.3L V6, 5.0L V8, and 5.7L V8 (1995 thru' 2005).
  • This is one of the easiest GM ignition control modules to test. This article will take you step by step through the whole process of diagnosing and troubleshooting a bad ignition control module and ignition coil.