TEST 2: Verifying The 12 Volt Start Signal
Up to this point, you've confirmed that the starter motor activates only when it receives battery power on its S terminal.
Your next step, and the focus of this section, is to verify that the wire connected to the S terminal is providing an activation signal when your helper turns the key to start the engine.
This activation signal is in the form of 10 to 12 Volts and is only present in the wire when the ignition key is turned to the START position.
I recommend using a multimeter to check for the 12 Volts activation signal when you turn the key to START position.
NOTE: You can perform this test with the 'S' wire connected or disconnected to the 'S' terminal.
These are the test steps:
- 1
Raise and place the front of the vehicle on jack stands (if it isn't already).
- 2
Place your multimeter in Volts DC mode.
- 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
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? It's 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
Have your helper turn the key to crank the engine when the test is setup.
- 6
Your multimeter should read 10 to 12 Volts DC.
OK, let's take a look at your test result:
CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct and expected test result and it confirms that the starter motor is receiving its activation signal.
Now, in most cases, 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 confirms the starter motor isn't receiving an activation signal. Without it, the starter motor will not activate and crank the engine.
The missing starter motor activation signal is most likely caused by one of the following issues:
- A bad starter motor relay.
- A bad park-neutral safety switch.
- A bad clutch pedal switch.
- A bad ignition switch.
- An anti-theft system fault.
Although it's beyond the scope of this tutorial, your next step is to find the cause of the missing activation signal and resolve the issue.
TEST 3: Voltage Drop Testing The Battery (+) Cable
As you're already aware, the starter motor has a thick cable connecting to it (it attaches to the stud labeled with the "+" symbol in the illustration above).
This thick wire (cable) connects the starter motor directly to the battery positive (+) post.
The starter motor receives the current it needs to crank the engine via this BAT (+) cable.
It's not uncommon for the cable's round terminals to corrode, resulting in the starter not cranking the engine.
You'll perform a simple multimeter voltage drop test on the cable to see if there's any hidden corrosion on its terminal ends (which may be keeping the starter motor from functioning).
NOTE: The BAT (+) cable should remain attached to the solenoid for this test.
These are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 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
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
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
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 interpret your test result:
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 confirms that the starter's battery (+) cable has corrosion on one or both terminal ends.
The issue causing the voltage drop in the cable will prevent the battery's total amperage output from reaching the starter motor.
Your next step is thoroughly cleaning both ends of the battery positive (+) cable with a small piece of sandpaper.
Eliminating the cause of the voltage drop should get the starter motor to crank the engine.
More 3.1L Buick Regal And Oldsmobile Cutlass Supreme Test Tutorials
If this tutorial was helpful, be sure and take a look at all of the 3.1L Buick Regal and Oldsmobile Cutlass Supreme diagnostic tutorials in this index:
Here's a sample of the tutorials you'll find there:
- How To Test The Fuel Pump (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
- How To Test The TPS (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
- How To Test The Alternator (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).
- How To Test A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
If this info saved the day, buy me a beer!
