How To Test The Alternator (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme)

TEST 3: Checking The Battery Voltage Sense Circuit Wire

As the engine runs, the alternator's voltage regulator must sense the current battery voltage.

The wire that provides battery voltage information to the voltage regulator is labeled with the letter S in the illustration above.

The illustration above shows the front view of the alternator 3-wire pigtail connector.

The battery voltage sense wire is protected by an inline fusible link which we need to make sure is not blown.

To check the integrity of this inline fusible link, we'll do a multimeter continuity test on the wire.

Let's get started:

1. 1

   Disconnect the battery negative (-) cable from the battery but leave the positive (+) cable connected to the positive (+) post.
   
   IMPORTANT: Do not proceed to the next steps until you do this first.

2. 2

   Disconnect the 3-wire pigtail connector from the alternator.

3. 3

   Set your multimeter to Ohms mode.

4. 4

   Connect the red multimeter test lead to the battery positive (+) terminal.
   
   IMPORTANT: The multimeter test lead must connect to a clean spot on the battery's positive (+) terminal

5. 5

   Connect the black multimeter test lead to the female terminal labeled with the letter S of the alternator's 3-wire pigtail connector (see the illustration above).

6. 6

   Your multimeter should register continuity, usually an Ohms reading of less than 1 Ohm.

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

CASE 1: The multimeter registered continuity. This is the correct and expected test result and confirms the battery voltage sense wire's inline fusible link is OK.

Your next step is to go to: TEST 4: Making Sure The ALT Fuse Is Not Blown.

CASE 2: The multimeter reports the wire has an open-circuit problem (usually by displaying the letters OL). This tells you the inline fusible link protecting the battery voltage sense wire is blown.

Your next step is to replace the inline fusible link and retest the battery's voltage with the engine running (TEST 1).

TEST 4: Making Sure The ALT Fuse Is Not Blown

Alright, for our last test, we'll ensure that the alternator fuse supplies 10 to 12 Volts DC to the female terminal labeled with the letter F (see illustration above).

The alternator fuse is located in the engine compartment fuse box, and depending on your vehicle's model year, it's labeled with one of the following names:

Buick:

• 1989-1990 3.1L Buick Regal: IGN/ALT Fuse 13.
• 1991-1992 3.1L Buick Regal: IGN Fuse.
• 1994-1996 3.1L Buick Regal: FAN/ALT Fuse.

Oldsmobile:

• 1989 3.1L Oldsmobile Cutlass Supreme: IGN Fuse 13.
• 1990 3.1L Oldsmobile Cutlass Supreme: IGN Fuse or ALT fuse.
• 1991-1993 3.1L Oldsmobile Cutlass Supreme: IGN Fuse.

These are the test steps:

1. 1

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

2. 2

   Disconnect the 3-wire pigtail connector from the alternator.

3. 3

   Connect the black multimeter test lead to the battery negative (-) terminal.
   
   IMPORTANT: The multimeter test lead must connect to a clean spot on the battery's negative (-) terminal

4. 4

   Connect the red multimeter test lead to the female terminal labeled with the letter F of the alternator's 3-wire pigtail connector (see the illustration above).

5. 5

   Have your helper turn the key to the ON position (RUN position) but ask him NOT to crank the engine.

6. 6

   Your multimeter should register 10 to 12 Volts DC.

Let's analyze your test result:

CASE 1: The multimeter registered 10 to 12 Volts DC. This is the correct and expected test result and confirms the alternator fuse is OK.

You can conclude the alternator is bad if you have:

• Confirmed the battery's voltage is below 12.5 Volts DC and continues to fall as the engine runs (TEST 1).
• Confirmed the inline fusible link that protect the alternator's output wire is not blown (TEST 2).
• Confirmed the battery voltage sense wire's inline fusible link is not blown (TEST 3).
• In this test section, you've confirmed the alternator fuse is OK.

CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. Replace the ALT fuse with a fuse of the same rating and repeat TEST 1.

If the alternator still does not charge the battery, you can conclude it's bad (and needs replacement) if you have:

• Confirmed the battery's voltage is below 12.5 Volts DC as the engine runs (TEST 1).
• Confirmed all fuses (inline fusible links and ALT fuse) are OK (TEST 2, TEST 3, TEST 4).

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:

• GM 3.1L Index Of Articles.

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 A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
• How To Test The Starter Motor (1989-1993 3.1L V6 Buick Regal, Oldsmobile Cutlass Supreme).