How To Test The Starter Motor (1995-1999 3.1L V6 Chevrolet Lumina, Monte Carlo)

TEST 2: Testing The START Signal At The Starter Solenoid

So far, you've confirmed that the starter motor does function, but only when you directly pass 12 Volts DC to its 'S' terminal (TEST 1).

In this test section, we're gonna' see if the starter motor is receiving a START signal from the ignition switch.

The START signal is only sent to the starter motor when you turn the ignition switch key to the START position.

OK, this is what you'll need to do:

1. 1

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

2. 2

   Connect the black multimeter test lead to the battery negative (-) terminal.

3. 3

   Connect the red multimeter test lead to the wire that attaches to the S terminal of the starter motor solenoid.
   
   The easiest way to do this is using a tool like a wire piercing probe, to pierce this wire and then attach the multimeter test 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 is the one that delivers the START signal from the ignition switch (the orange arrow points to this S terminal in the photo in the photo above).

4. 4

   Place your multimeter on Volts DC mode.

5. 5

   When everything is set and ready, have your helper turn the key to the START position 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 START signal from the ignition switch.

6. 6

   Your multimeter will register one of two results:
   
   1.) 0 Volts.
   
   2.) 10 to 12 Volts DC.

OK, let's interpret your test results:

CASE 1: Your multimeter DID NOT register 10 to 12 Volts. This result lets you know that the reason the starter motor is not cranking the engine is because it's not receiving a START signal.

To find out why, we need to continue on with our diagnostic. Go to: TEST 4: Testing The START Signal (Anti-Theft Relay).

CASE 2: Your multimeter registered 10 to 12 Volts. This is the correct test result and it lets you know that the starter motor is getting a START signal.

This test result also confirms that the following components are OK:

• The ignition switch is OK.
• The neutral safety switch is good and doing its job.
• The Pass-Key System (anti-theft system) is letting the START signal reach the starter motor.

If the starter motor does not function, even after confirming that it does crank the engine with a remote start switch (TEST 1) and that it's getting a START signal (this test section), I recommend:

• Checking that the 2 wires that connect to the starter motor solenoid are not loose.
• Removing the starter motor and checking for any damage to the starter motor solenoid.
• Checking and cleaning any corrosion present in the terminals that connect to the starter motor solenoid.

TEST 3: Voltage Drop Testing The Battery Wire

Up to this point, you have verified that:

• The battery is fully charged and its terminals are clean.
• The starter motor cranks the engine when you directly applied 12 Volts to its S terminal with a remote start switch (TEST 1).

The next step is to make sure that the positive (+) battery cable that attaches to the starter motor's solenoid is supplying full battery voltage and amperage to the starter motor.

In other words, we need to make sure that there isn't any hidden corrosion somewhere on the cable holding back any battery power to the starter motor.

We'll accomplish this check for 'hidden corrosion' by doing a simple voltage drop test.

IMPORTANT: The battery must remain connected to its two battery cables for the voltage drop test to work.

These are the test steps:

1. 1

   Connect the red multimeter test lead to the center of the bolt that attaches to the positive (+) battery cable to the battery.
   
   The spot on this bolt, which the multimeter test lead will be touching, has to be clean and rust-free.
   
   NOTE: 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 turn the key and attempt to crank the engine when everything is set up).

2. 2

   With the black multimeter test lead, touch the center of the starter solenoid stud that connects to the positive (+) battery cable.
   
   The orange arrow with the letter B, in the photo above, points to this starter motor solenoid stud.
   
   IMPORTANT: Maintain the black multimeter test lead in this position throughout the next step.

3. 3

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

4. 4

   The multimeter should register 0.5 Volts or less (0.5 V is really 0 Volts)
   
   If there's a problem in the wire (like corrosion or a loose connection), your multimeter will register a voltage of 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 result indicates that the starter motor is receiving all of the battery voltage/amperage it needs to crank the engine.

This result also confirms that the starter motor is bad and needs to be replaced if you have confirmed:

• That the starter motor DOES NOT crank the engine when you pass 12 Volts directly to it (TEST 1).
• That the battery cable, that attaches to the starter motor solenoid does not have a voltage drop (this test section).

Now, before you remove the starter motor, do two more things:

1.) Turn the engine manually (using a 1/2 ratchet and the appropriate socket on the crankshaft pulley) to make sure that the engine is not mechanically locked up.

2.) Bench test the starter motor. You can find the step-by-step instructions here: How To Bench Test A Starter Motor (Step By Step).

CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and as a result, the starter motor is not receiving all of the voltage/amperage it needs to crank the engine.

The solution is to simply disconnect the positive (+) battery cable from the battery and thoroughly clean it.

Also, the end of this very same cable, that's attached to the starter motor solenoid, should be disconnected, inspected and cleaned.

Cleaning the end that attaches to the starter motor solenoid should be done with a small piece of sand paper. 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 engine's no-crank condition, your vehicle will now crank and start.