How To Test The Starter Motor (1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer)

This tutorial will show you how to test the starter motor on your 4.0L Ford Explorer (Aerostar or Mercury Mountaineer) to see if it's the one responsible for your engine's no-crank problem.

The starter motor test is a pretty easy test that requires only a multimeter and a helper. You'll find all of the test instructions explained in a step-by-step manner.

NOTE: You'll notice that the photos I'm using are of the starter motor off of the vehicle. I've done this to make it easier to show you where to make your test connections. You don't need to remove the starter motor from your 4.0L Ford Ranger (Mazda B4000) to follow the test instructions in this tutorial.

Ford Ranger: You can find the 4.0L Ford Ranger (Mazda B4000) starter motor test tutorial here:

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.0L V6 Ford Aerostar: 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.
  • 4.0L V6 Ford Explorer: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
  • 4.0L V6 Mercury Mountaineer: 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.

En Español You can find this tutorial in Spanish here: Cómo Probar El Motor De Arranque (4.0L Ford) (at: autotecnico-online.com).

Important Testing Tips

The following testing tips will help you test the starter motor without complications:

TIP 1: The battery must have a full charge before starting any of the tests in this tutorial.

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 to familiarize yourself with the tests.

TIP 4: Use jack stands for safety. Don't trust the jack alone to keep your vehicle up in the air while you're underneath it!

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

Symptoms Of A Bad Starter Motor

Generally, the engine will not turn over when the starter motor fails (when you turn the key to start it).

Unfortunately, in some cases, the starter motor fails intermittently. When this happens, the starter motor functions most of the time, but now and then, it doesn't.

If your 4.0L Ford Explorer (Aerostar or Mercury Mountaineer) is experiencing an intermittent starter motor failure, you'll need to wait till the starter motor isn't cranking the engine to test it.

Tools Needed To Test The Starter Motor

The starter motor test doesn't require expensive or exotic testing equipment. Most of the tools you'll need you can find inexpensively at your local auto-parts store or online.

Here's a list of what you'll need:

  • Jack.
    • You'll need to raise your vehicle to gain access to the starter motor.
  • Jack stands.
  • A remote starter switch.
  • A multimeter or a 12 Volt automotive test light.
  • A wire piercing probe.
    • 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.
    • 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).
  • A helper.

TEST 1: Applying 12 Volts To The 'S' terminal

Applying 12 Volts To The 'S' terminal. How To Test The Starter Motor (1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer)

The first test you'll perform is to see if the starter motor activates (and cranks the engine) when you apply 12 Volts to its solenoid's 'S' terminal.

If the starter motor comes to life and cranks the engine, you can conclude that the starter motor itself is functioning correctly and that some other issue is keeping it from cranking the engine. Your next step will be to go to TEST 2.

If the starter motor does not crank the engine, you can generally conclude the starter motor is fried.

IMPORTANT: Remove the key from the ignition switch for this test.

OK, let's get testing:

  1. 1

    Raise your Ford Ranger (Mazda B4000) and place on it jack stands. Remember, the only way to gain access to the starter motor is from underneath the vehicle.

  2. 2

    Disconnect the battery negative (-) terminal.

    You'll reconnect it back in one of the following steps, for now, it's a safety precaution as you set up the test.

  3. 3

    Attach one end of the remote starter switch to the battery positive (+) post.

  4. 4

    Attach the other end of the remote starter switch to the 'S' terminal of the starter motor solenoid.

    This is easier said than done, so take your time and make sure the connection is on the 'S' terminal of the starter motor solenoid.

    Also, in case you're wondering, you can leave the starter motor solenoid's 'S' terminal wire connected to the engine's wiring harness connector or not, the test will work either way.

  5. 5

    Reconnect the battery negative (-) cable to the battery negative post.

  6. 6

    Apply 12 Volts to the 'S' terminal wire of the starter motor starter solenoid with your remote starter switch.

  7. 7

    You'll get one of two results:

    1.) The starter will activate and will turn over the engine.

    2.) The starter motor won't do a thing.

Let's take a look at what your test results mean:

CASE 1: The starter motor cranked the engine. This is the correct and expected test result.

You can conclude that the starter motor itself is OK. The next step is to see if the starter motor is getting the 12 Volt Start signal on the 'S' terminal wire. Go to: TEST 2: Verifying The 12 Volt Start Signal.

CASE 2: The starter motor DID NOT crank the engine. This usually means that your starter motor is bad and needs to be rebuilt or replaced.

I suggest you perform two more tests. First, make sure the starter motor is getting its 12 Volt Start signal. Second, voltage drop test the battery cable (that attaches to the starter motor solenoid).

Ford Vehicles:

  • Aerostar 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Explorer 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010

Mercury Vehicles:

  • Mountaineer 4.0L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010