TEST 3: Checking The Battery Voltage Sense Circuit Wire
To charge the battery, the alternator must sense the battery voltage while the engine is running.
The alternator's internal voltage regulator obtains this battery voltage sensing information from the wire connected to the terminal marked with the letter S in the figure above.
The battery voltage sensing wire is also protected by an inline fuse, and we need to make sure it hasn't blown.
As in the previous test, we'll verify the integrity of this inline fuse with a multimeter continuity test.
These are the test steps:
- 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
Disconnect the 3-wire pigtail connector from the alternator.
- 3
Set your multimeter to Ohms mode.
- 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
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
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
For our final test, let's make sure the terminal marked with the letter F (in the image above) has 10 to 12 Volts when the key is in the "RUN" position.
The F terminal gets these 10 to 12 Volts from a fuse in the instrument panel fuse box.
The instrument panel alternator fuse is labeled with a different name depending on the model year of your particular vehicle.
You can identify the fuse in the table here: Identifying The Alternator Fuse.
These are the test steps:
- 1
Reconnect the negative (-) battery cable to the battery's negative (-) post,.
- 2
Disconnect the 3-wire pigtail connector from the alternator.
- 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
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
Have your helper turn the key to the ON position (RUN position) but ask him NOT to crank the engine.
- 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).
Identifying The Alternator Fuse
| 3.1L V6 Chevrolet Alternator Fuse ID | ||
|---|---|---|
| Model | Year | Fuse Name |
| Beretta | 1990-1993 | Fuse 4 (I/P Fuse Block) |
| Cavalier | 1990 | Fuse 16 or HTR-AC Fuse (I/P Fuse Block) |
| Cavalier | 1991-1994 | HTR-AC Fuse (I/P Fuse Block) |
| Celebrity | 1990 | FAN/ELEC Fuse (I/P Fuse Block) |
| Corsica | 1990-1993 | Fuse 4 (I/P Fuse Block) |
| Lumina | 1990 | ALT Fuse (Engine Compartment Fuse Block) |
| Lumina | 1991-1993 | IGN Fuse (Engine Compartment Fuse Block) |
| 3.1L V6 Pontiac Alternator Fuse ID | ||
|---|---|---|
| Model | Year | Fuse Name |
| 6000 | 1990-1991 | FAN/ELEC Fuse (Engine Compartment Fuse Block) |
| Grand Prix | 1990 | ALT Fuse (Engine Compartment Fuse Block) |
| Grand Prix | 1991-1993 | IGN Fuse (Engine Compartment Fuse Block) |
| Sunbird | 1991-1994 | HTR-AC Fuse (I/P Fuse Block) |
More 3.1L Chevrolet And Pontiac Diagnostic Tutorials
You can find a complete list of 3.1L Chevrolet and Pontiac diagnostic tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The Fuel Pump (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The TPS (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The Engine Compression (3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The Starter Motor (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
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