The alternator on the 2001-2003 4.3L V6 Chevrolet S10 pickup and GMC Sonoma is a computer controlled alternator that can easily be tested with a multimeter.
In this tutorial, you'll find the three tests you need to run on the alternator to find out if it's good or bad.
NOTE: This is an on-car alternator test. No need to remove it to test it.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Alternador (2001-2003 4.3L V6 Chevrolet S10 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 4.3L V6 Chevrolet S10 Pickup: 2001, 2002, 2003.
- 4.3L V6 Chevrolet Sonoma: 2001, 2002, 2003.
Important Testing Tips
TIP 1: The battery must be fully charged for the alternator test described in this tutorial to work properly.
If your battery is low on charge, charge it before testing the alternator.
TIP 2: You can use a digital multimeter or an analog multimeter.
TIP 3: Please take all necessary safety precautions! You'll be working around a running engine, so always be careful and stay alert.
Symptoms Of A Bad Alternator
The alternator has two important jobs to do:
- Charge the battery after cranking and starting the engine.
- Provide the power needed to run your vehicle's accessories (headlights, wipers, blower motor, etc.)
When the alternator stops working and does not charge the battery, you'll see one or more of the following symptoms:
- The charge light (also known as the battery light) will be shining nice and bright on your vehicle's instrument cluster.
- Whenever you turn on the headlights (night driving), they glow very dim.
- The car won't crank. It'll only crank and start if you jump start your vehicle.
- The only way the engine will crank and start is to charge the battery.
TEST 1: Checking Battery Voltage With The Engine Running
To get our alternator diagnostic started, we'll start the engine and check the battery's voltage.
With the engine running, your battery's voltage should be between 13.5 to 14.5 Volts DC.
If your multimeter reports a voltage between 13.5 to 14.5 Volts DC, you can conclude that the alternator is charging the battery.
If the alternator isn't charging battery, your multimeter will report a battery voltage of around 12.5 Volts DC which will decrease the longer the engine stays running.
NOTE: If you don't have a multimeter or need to upgrade yours, take a look at my recommendatin here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
Let's get going:
Start the engine and let it idle.
Place your multimeter in Volts DC mode.
Check the battery's voltage with your multimeter.
The multimeter should register 13.5 to 14.5 Volts.
If it doesn't, don't worry about this just yet, continue to the next step.
Turn on every accessory possible while observing the multimeter. Like the headlights, the A/C or heater (high blower speed), the windshield wipers, the radio, the rear window defroster, etc.
As each accessory comes on, they'll place a load on the charging system (alternator).
As each accessory comes on, your multimeter will do one of two things:
1.) The multimeter's voltage reading will decrease slightly and then stabilize around 13.5 to 14.5 Volts DC (when something comes on).
2.) The DC voltage reading will decrease to 10 Volts DC.
Let's interpret your test results:
CASE 1: Battery voltage remained at a value of 13.5 to 14.5 volts throughout the test. This is the correct test result and indicates that the alternator is working properly.
Since the alternator is charging the battery, no further testing is required.
CASE 2: Battery voltage DID NOT remain at a value of 13.5 to 14.5 volts throughout the test. This test result confirms that the alternator is not charging the battery.
The next step is to test the continuity of the wire connecting the alternator to the battery. For this test go to: TEST 2: Testing The Continuity Of The Alternator's Output Wire.
TEST 2: Testing The Continuity Of The Alternator's Output Wire
The alternator is connected to the battery with a cable. This cable, commonly known as the B+ circuit, supplies the alternator's current output to the battery.
The B+ circuit cable connects to the stud on the back of the alternator. In the image above, I've labeled the stud with the orange arrow with the '+' symbol.
This cable is protected by an inline fusible link and this test section focuses on checking if it's good or blown.
We can easily check the integrity of this inline fusible link with a continuity test using a multimeter.
NOTE: The photo above is with the alternator removed from the vehicle to better illustrate the test connections. Do not remove the alternator from the vehicle to perform this test.
These are the test steps:
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 step until you do this first.
Set your multimeter to Ohms mode.
Connect the black multimeter test lead to the stud shown in the photo above.
The alternator's output wire connects to the stud the arrow points to (in the photo above).
Connect the red multimeter test lead to the positive (+) terminal of the battery.
The battery negative (-) cable must remain disconnected from the battery.
Your multimeter will register one of two values:
1.) Continuity (usually an Ohms value of about 0.5 Ohms).
2.) No continuity (an infinite Ohms reading (OL)).
OK, let's interpret your test results:
CASE 1: Your multimeter registered continuity (usually 0.5 Ohms). This is the correct and expected test result and it tells you that the inline fusible link protecting the alternator output cable is OK.
Your next step is to go to: TEST 3: Making Sure The Alternator Is Getting An Activation Signal.
CASE 2: Your multimeter DID NOT register continuity, it registered OL. This test result confirms the inline fusible link protecting this wire is blown.
Your next step is to replace the inline fusible link and retest.