How To Test The Starter Motor (Ford 4.0L Explorer, Ranger, Aerostar)

This article will show you how to test the starter motor on your 4.0L Ford Explorer (or 4.0L Ranger, or 4.0L Aerostar, or 4.0L Mountaineer) to see if it's the one responsible for your vehicle not cranking.

This is a pretty easy test which only requires a multimeter and a helper to do and you'll find the step-by-step test instructions here.

To see if this starter motor test article covers your specific Ford or Mercury 4.0L equipped pick up, mini-van or SUV, 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 links.

NOTE: You'll notice that the photos I'm using are of the starter motor off of the vehicle... this is just to make it easier to show you where to make your test connections. You don't need to remove the starter motor from your Ford to follow the test instructions in this tutorial.

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

  1. Important Tips.
  2. Symptoms of BAD Starter Motor.
  3. Tools Needed To Test The Starter Motor.
  4. STARTER TEST 1: Applying 12 Volts to the S Terminal.
  5. STARTER TEST 2: Verifying The 12 Volt Start Signal.
  6. STARTER TEST 3: Voltage Drop Testing The Batt (+) Cable.
  7. Related Test Articles.

En Español You can find this tutorial in Spanish here: Cómo Probar el Motor de Arranque (4.0L Ford) (at:

Important Tips

To succesfully accomplish the tests in this article, I suggest you follow these tips:

TIP 1: Before doing the starter motor test on your 4.0L Ford pick up (or mini-van, SUV), you need to verify the battery's state of charge, since the battery has to be fully charged for any of the tests in this tutorial to work.

TIP 2: The battery cable terminals and the battery posts should be clean and corrosion free before starting the tests.

TIP 3: Read the entire article first so that you can familiarize yourself with the tests.

TIP 4: Since you'll need to raise your Ford pick up (or mini-van or SUV) up in the air to access the starter motor, use jack stands for safety. Do not trust the jack alone to keep you vehicle up in the air while you're underneath it!

TIP 5: Take all necessary safety precautions, like use safety glasses while working underneath the vehicle. Be alert and think safety all of the time.

Symptoms Of A BAD Starter Motor

When the starter motor goes BAD on your Ford Explorer (Ranger, Aerostar, or Mountaineer) you'll see one or several of the following symptoms:

  1. You turn the key to crank up and start the engine but nothing happens.
  2. You got someone to help your jump-start your Ford, but this didn't help get the engine to crank and start.
  3. You've bought a brand new battery (thinking that was the solution to the No Crank Condition) and this did not get your Ford to crank and start.
  4. Turn the key to start your Ford and all you hear is a small knock and nothing else.

Although the above list is a not a very complete list of symptoms... the theme that runs thru' them, and any other related symptom, is that the engine will not turn over when the key is turned to crank the vehicle.

Tools Needed To Test The Starter Motor

You don't need expensive test equipment to test the starter motor on your 4.0L Ford Explorer (Ranger, Aerostar, or Mountaineer)... but you do need a few things. These are:

  1. Jack.
    1. You'll need to raise your vehicle to gain access to the starter motor.
  2. Jack stands.
  3. Remote starter switch.
    1. If you'd like to see what a remote starter switch looks like, you can follow this link: Actron CP7853 Remote Starter Switch.
    2. You can either buy this tool online or you can buy it at your local auto parts store (AutoZone, O'Reilly, Pepboys, etc.).
  4. Multimeter or a 12 Volt automotive test light.
    1. If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at:
  5. A wire piercing probe.
    1. This tool is not an ‘absolute must have tool’ but I can tell you from experience that it makes it a whole lot easier to probe the S terminal wire for the Start Signal.
    2. If you'd like to see what this tool looks like, you find out more about it here: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01).
  6. A helper.

As you can see... you don't need anything expensive. OK, let's turn the page and get starter with the first starter motor test.