Testing the alternator isn't difficult at all, and the cool thing is you can use a simple multimeter to accurately determine if it's good or bad. No expensive diagnostic equipment is needed!
In this tutorial, I'll explain how to test the alternator step by step. Your test results will tell you if the alternator has failed and isn't charging the battery anymore.
Contents of this tutorial:
- Important Testing Tips.
- Symptoms Of A Bad Alternator.
- TEST 1: Checking Alternator Voltage Output With A Multimeter.
- TEST 2: Testing The Continuity Of The Alternator's Output Wire.
- TEST 3: Checking The Battery Voltage Sense Circuit Wire.
- TEST 4: Making Sure The Alternator Fuse Is Not Blown.
- TEST 5: Checking The Alternator's L Circuit.
- More 2.2L Buick Century And Oldsmobile Cutlass Ciera Test Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Alternador (1992-1995 2.2L Beretta, Cavalier, Corsica, Sunfire) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.2L Chevrolet Beretta: 1992, 1993, 1994, 1995.
- 2.2L Chevrolet Cavalier: 1992, 1993, 1994, 1995.
- 2.2L Chevrolet Corsica: 1992, 1993, 1994, 1995.
- 2.2L Pontiac Sunfire: 1995.
Important Testing Tips
TIP 1: Before you start the alternator tests, make sure the battery is fully charged (since you'll have to crank and start the engine to test the alternator).
TIP 2: You can use a digital multimeter or an analog multimeter.
TIP 3: Take all necessary safety precautions. Be alert and think safety all of the time since you'll be working around a running engine.
Symptoms Of A Bad Alternator
The alternator is the component that charges the battery after the engine has started.
It also provides the voltage and amperage your vehicle's electrical accessories need to run.
If the alternator fails, then it stops charging the battery and the car will run until the battery discharges.
When the alternator fails you're going to 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 will only crank and start if you jump start your vehicle.
- The only way the car cranks and starts is if you charge the battery.
TEST 1: Checking Alternator Voltage Output With A Multimeter
If the alternator is charging the battery, the battery's voltage will be between 13.5 to 14.5 Volts DC (while the engine is running).
If the alternator has failed, you'll see a battery voltage of around 12 volts, decreasing the longer the engine runs.
So for our first test, we'll check the battery voltage with the engine running.
These are the test steps:
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 analyze your multimeter test results:
CASE 1: The multimeter maintained a 13.5 to 14.5 Volts value thru' out the whole test. This is the correct test result and it tells you the alternator is functioning correctly.
Since the alternator is charging the battery, no further testing is required.
CASE 2: The multimeter DID NOT maintain a 13.5 to 14.5 Volts value. This test result confirms that the alternator is not charging the battery.
The next step is to test the continuity of the wire that connects 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 delivers the amperage and voltage it produces to the battery via a single cable.
This cable connects to the stud located in the rear of the alternator. In the illustration above, I've labeled this stud with the orange arrow with the '+' symbol.
An inline fusible link protects the cable (that connects to this stud), and it's not uncommon for it (the fusible link) to get blown.
When the fusible link gets blown, none of the alternator's output will reach the battery.
In this test section, you'll check the cable's continuity to ensure that it doesn't have an open-circuit problem (caused by a blown inline fusible link).
OK, let's start:
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.
Set your multimeter to Ohms mode.
Connect the red 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 black multimeter test lead on the battery positive (+) terminal (at the battery).
The battery negative (-) wire 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's output wire is OK.
So far, it's looking like the alternator is bad. There's still one more test to do, go to: TEST 3: Checking The Battery Voltage Sense Circuit Wire.
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.