How To Test The Starter Motor (1990-2004 3.1L V6 Buick, Oldsmobile)

TEST 2: Verifying The 12 Volt Start Signal

As you're already aware, the starter motor gets an activation signal when you turn the key to crank and start the engine.

This activation signal is delivered by the wire that connects to the starter motor solenoid's 'S' terminal.

In this test section, you'll ensure that this activation signal is present in this wire by doing a multimeter voltage test on it.

NOTE: You can perform this test with the wire connected or disconnected to the 'S' terminal.

Alright, these are the test steps:

1. 1

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

2. 2

   Grab and set your multimeter on Volts DC mode.

3. 3

   Ground the black multimeter test lead directly on the negative (-) battery terminal using a jump start cable.
   
   You can also Ground it on the engine, if you can find a clean, unpainted and rust-free spot of metal.

4. 4

   Connect the red multimeter test lead to the 'S' terminal wire using an appropriate tool.
   
   Don't know which wire is the 'S' terminal wire? This is the one that connects to the smaller of the three studs on the starter motor solenoid.
   
   The 'S' terminal wire (circuit) is the one that delivers the Start (Crank) signal from the ignition switch.

5. 5

   Have your helper turn the key to crank the engine when the test is setup.

6. 6

   Your multimeter should read 10 to 12 Volts DC.

OK, let's interpret your test results:

CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct and expected test result, and it confirms that the 'S' terminal wire is delivering an activation signal.

You could stop here and 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.

Your next test is to voltage drop test the battery positive (+) cable. This is a very easy and simple test to do. Go to: TEST 3: Voltage Drop Testing The Battery (+) Cable.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This test result lets you know that the 'S' terminal wire is not delivering an activation signal.

Although finding out why this activation signal is missing is beyond the scope of this tutorial, the most likely causes are:

• A bad park-neutral safety switch.
• A bad clutch pedal switch.
• A bad ignition switch.
• An anti-theft system problem (if equipped).

TEST 3: Voltage Drop Testing The Battery (+) Cable

If the starter motor doesn't receive the battery's total amperage output, it will not crank the engine.

In many cases, hidden corrosion or a false-contact connection will cause the starter motor not to crank the engine.

The check if the starter motor's battery wire has such a problem, you'll do a multimeter voltage drop test on it.

These are the test steps:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Attach the red multimeter test lead to the positive (+) battery post. The positive (+) battery post must be clean and corrosion-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

   Place the black multimeter test lead on the starter motor solenoid stud that connects to the battery positive (+) cable (see illustration above).
   
   The orange arrow with the plus (+) sign, in the illustration above, points to this stud.
   
   Maintain the black multimeter test lead in this position throughout the next step.

4. 4

   When everything is ready, have your helper turn the key to crank the engine.
   
   Although the starter motor won't crank the engine, your helper has to turn the ignition switch to start the engine for the voltage drop test to work.

5. 5

   The multimeter should register 0.5 Volts or less (0.5 V = 0 Volts).
   
   If there's a problem in the wire, your multimeter will register some voltage, usually 5 Volts or more.

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 is the correct test result, and it confirms the starter motor is receiving all of the battery voltage and amperage it needs to crank the engine.

You can conclude that the starter motor is bad and needs replacement if you have:

• Confirmed that the starter motor does not crank the engine (TEST 1).
• Confirmed that the starter motor is receiving an activation signal (TEST 2).
• Confirmed, in this test section, that the battery positive (+) cable does not have a voltage drop issue.

Now, before you remove the starter motor, do one more important thing:

• Turn the engine manually (using a 1/2 ratchet and the appropriate socket on the crankshaft pulley bolt). This will check to see if the engine is mechanically locked up (or not).

If you'd like to bench test the starter motor (after removing it). You can find the step-by-step instructions here:

• How To Bench Test A Starter Motor (Step By Step) (at: easyautodiagnostics.com).

CASE 2: Your multimeter registered 5 Volts or more. This result tells you the starter motor's battery wire has a problem.

The voltage drop in the battery wire will prevent the battery's total amperage output from reaching the starter motor.

To solve this problem, you'll need to thoroughly clean both ends of the battery positive (+) cable.

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

More 3.1L V6 Buick, Oldsmobile Tutorials

You can find a complete list of 3.1L V6 Buick (Oldsmobile) tutorials in this index:

• GM 3.1L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test Engine Compression Test (3.1L V6 Buick, Oldsmobile).
• How To Test A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
• How To Test The Fuel Pump (3.1L V6 Buick, Oldsmobile).
• How To Test The 24X Crankshaft Position Sensor (1995-1997 3.1L V6 Oldsmobile Cutlass Supreme).