How To Test The Starter Motor (GM 3.8L)

Testing the starter motor on any GM 3.8L equipped car or mini-van (to find out if it's the one causing your car or mini-van not to crank) can be done in two easy tests and in this article, I'll show you how.

With the step by step test instruction in this article, you should be able to accomplish the starter motor test in under 30 minutes, using only a multimeter and a helper.

To see if this starter motor test article covers your specific Chevy or Buick or Olds or Pontiac 3.8L equipped vehicle, you can take a look at the list of applications on the box labeled ‘Applies To:’ on the column on the right and scroll with the prev and next arrow buttons.

Here are the contents of this article at a quick glance:

  1. STARTER TEST 1: Testing The Starter Solenoid 'S' Signal.
  2. STARTER TEST 2: Applying 12 V To The S Terminal.
  3. STARTER TEST 3: Voltage Drop Testing The Battery Circuit.
  4. Symptoms Of A BAD Starter Motor.
  5. Related Test Articles.

STARTER TEST 1: Testing The Starter Solenoid 'S' Signal

How To Test The Starter Motor (GM 3.8L)

Before you start testing, you need to make sure that the battery is fully charged. A low battery can make you think that the starter motor is BAD when it really isn't.

Also, you need to remove the battery cable terminals from the battery and check for corrosion on them. If corroded, please clean and crank the car (or mini-van) to see if this solves the No Crank Condition and/or before proceeding with the test.

Lastly, you'll need to access the starter motor from underneath your car or mini-van... so please take all necessary safety precautions, like using safety glasses, jack stands, etc.

OK, to get this show on the road, this is what you'll need to do:

  1. 1

    Raise the front of your 3.8L equipped GM car or mini-van (using a jack) and place it on jack stands.

  2. 2

    Grab and set your multimeter on Volts DC mode.

  1. 3

    Probe the wire that attaches to the S terminal of the starter motor solenoid with the RED multimeter test lead. The easiest way to do this is using a tool like a Wire Piercing Probe, to pierce this wire and then attach the multimeter lead to it.

    Which is the S terminal wire? This is the wire that connects with a nut to the smaller of the three studs on the starter solenoid. This S terminal wire (circuit) is the one that delivers the Start (Crank) signal from the ignition switch (the orange arrow points to this S terminal in the photo in the image viewer).

  2. 4

    Ground the multimeter's BLACK test lead. I'm gonna' recommend that you use a battery jump start cable to ground the multimeter's test lead directly on the battery's negative terminal. This way you can ensure that you're gonna' have a good path to ground, since you may you may NOT be able to find a clean and rust-free spot on the bottom of the vehicle to ground the multimeter's BLACK lead.

  3. 5

    When everything is set and ready, have your helper turn the key to crank the engine.

    The starter motor won't crank the car, of course, but this is the only way to verify the presence of the Crank (Start) signal from the ignition switch.

  4. 6

    As your helper is cranking the engine, your multimeter will register one of two results: Either 10 to 12 Volts DC or 0 Volts.

    Alright, let's jump to the next page to interpret the results of this test...

OK, let's make sense of the readings that your multimeter recorded in the test:

CASE 1: If 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.

TEST TIP: Although you have verified that the starter motor is getting the crank signal from the ignition switch, I suggest that you apply 12 Volts directly to the S terminal of the starter motor solenoid (with a jumper wire connected to the battery positive terminal). STARTER TEST 2 I'll show you how to do it. Go to TEST 2


CASE 2: If your multimeter DID NOT register 10 to 12 Volts: This result let's 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 the ignition switch's crank signal, the starter motor will not crank the engine. This signal could be missing because either the neutral safety switch is BAD or because ignition switch itself is fried. Testing these two components is beyond the scope of this article... but you have now eliminated the starter motor as BAD.

I recommend one more test, and this is to apply 12 volts to the starter solenoid's S terminal. Go to TEST 2.