How To Test The Alternator (1994-1997 2.2L Chevrolet S10, GMC Sonoma)

TEST 3: Making Sure The Alternator Fuse Is Not Blown (1994 Only)

The focus of this last test section is to make sure that the voltage regulator's field coil circuit is receiving 12 Volts.

These 12 Volts are supplied by the pink with black stripe (PNK/BLK) wire connecting to terminal C of the alternator's 2-wire connector.

In turn, the terminal C wire connects to the GAUGES fuse in the instrument panel's fuse box.

We'll check for the presence of 12 Volts with the key on engine off (KOEO) at terminal F of the connector.

NOTE: The alternator fuse is located in the instrument panel fuse box, and it' s labeled as the GAUGES fuse.

IMPORTANT: This test section only applies to the 1994 model year 2.2L Chevrolet S10 and GMC Sonoma.

These are the test steps:

1. 1

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

2. 2

   Disconnect the 2-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 C of the alternator's 2-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.

Your next step is to ensure that the alternator is receiving an activation signal. Go to: TEST 4: Checking The Alternator's Activation Signal

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

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

• Confirmed that battery voltage is below 12.5 Volts DC as the engine runs (TEST 1).
• Confirmed that the alternator's output cable' s inline fusible links is OK (TEST 2).
• Confirmed in this test section that the GAUGES fuse is OK.

TEST 4: Checking The Alternator's Activation Signal

The alternator's voltage regulator gets an activation signal to start charging the battery when you crank and start the engine.

This activation signal is in the form of 12 Volts and are delivered to the alternator by the brown (BRN) wire of the alternator's 2-wire connector (1994) or 1-wire connector (1995-1997).

In the illustrations of the alternator connectors above, the BRN wire connects to the terminal labeled with the letter B.

These are the test steps:

1. 1

   With the engine off, disconnect the alternator from its 1-wire or 2-wire electrical connector.

2. 2

   Connect the red multimeter test lead to the brown (BRN) wire of the alternator's connector.
   
   NOTE: The safest/easiest way to connect the red multimeter test lead to the wire is with a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe.

3. 3

   Reconnect the alternator to its electrical 1-wire or 2-wire connector.
   
   CAUTION: Make sure the multimeter and test leads/wires are clear of the serpentine belt and any engine moving parts.

4. 4

   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

5. 5

   Have your helper turn the key to the ON position. No need to crank and start 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 test result and it tells you that the alternator is receiving an activation signal.

You can conclude that the alternator is bad if you have:

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

CASE 2: The multimeter DID NOT register the indicated voltage. Without this activation signal, the alternator will not turn on and charge the battery.

The most likely cause of this missing 12 Volts activation signal is:

• Blown GAUGES fuse (located in the dash fuse box).
• Blown battery indicator lamp (in the instrument panel).
• An open-circuit problem in the BRN wire between the alternator connector, the instrument panel or the GAUGES fuse.