How to Test the Starter Motor
(Jeep 4.0L)

How to Test the Starter Motor (Jeep 4.0L)

Testing the starter motor, to see if it's the cause of the No Crank Condition on your Jeep, is not that hard.

As a matter-o'-fact, testing the starter motor, to see if it's good or bad, is something that you can do at home. In this tutorial I'll show you how to do it in a step-by-step manner.

The contents of this article at a quick glance:

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

Important Safety Precautions

Suggestion 1: You'll notice that all of the photos I'm using show the starter motor off of the vehicle, well, this is only to make it easier to explain where you need to make your connections. You don't need to remove the starter motor to test it.

In case you do need to bench test it (test it off of the vehicle), the following tutorial will help you: How to Bench Test a Starter Motor (Step by Step) (at: easyautodiagnostics.com).

Suggestion 2: Before you start testing the starter motor, with the info in this tutorial, you need to make sure that the battey is fully charged. A discharged battery will cause you to reach the wrong diagnostic conclusion and have you wasting time and money! Also, the battery cable terminals and battery posts must be clean and corrosion free.

In a lot's of cases, dirty battery cables and/or battery posts are the culprit behind a No Crank Condition... and cleaning the battery cables and posts may actually solve your particular No Crank problem.

Suggestion 3: You'll need to raise your Jeep 4.0L equipped vehicle up in the air to access the starter motor... so, use jack stands... don't trust the jack alone! Take all necessary safety precautions, like using jack stands to hold up the vehicle, wearing eye-protection (safety glasses), etc.

Suggestion 4: If you're vehicle has a standard transmission... make sure that it's out of gear and in neutral, and the parking brake is activated/on.

Symptoms of a BAD Starter Motor

When the starter motor goes BAD on your Jeep vehicle, it will not crank the engine (this is called a No Crank Condition in tech speak). This condition (a No Crank Condition) is sometimes confused with a No Start Condition.

In a No Start Condition... the starter motor is cranking the engine, but the engine is not starting. The No Start Condition is usually due to a lack of Spark (think bad ignition coil or bad crank sensor), or a Lack of Fuel (think bad fuel pump). Knowing the difference between a No Crank and a No Start condition will save you some diagnostic time.

In a bona-fide No Crank Condition, you'll also see one or several of the following symptoms:

  1. The engine doesn't turn over (crank) when you turn the key to start the engine.
  2. A jump start doesn't help. The vehicle's engine still refuses to crank.
  3. The battery has been charged and/or replaced and still your vehicle does not crank.
  4. When you turn the key to crank the engine, 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 you try to start it.

Tools Needed to Test the Starter Motor

You don't need expensive test equipment to test the starter motor on your Jeep vehicle... but you do need a few things. These are:

  1. Jack.
  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: Abe's Multimeter Recommendation (at: easyautodiagnostics.com).
  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.

Jeep Vehicles:

  • Cherokee 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
  • Comanche 4.0L
    • 1987, 1988, 1989, 1990, 1991, 1992
  • Grand Cherokee 4.0L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

Jeep Vehicles:

  • Wagoneer 4.0L
    • 1987, 1988, 1989, 1990
  • Wrangler 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004

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