Personal Methods for Checking an Alternator

QuestionsCategory: Ask An ExpertPersonal Methods for Checking an Alternator
James McAllister asked 2 months ago
I'm curious about how car experts personally check an alternator. Do they recommend taking the car to a service center for testing, use a multimeter to check the battery voltage while running, or try the old method of starting the car and removing the negative battery cable? I've heard that this last method can be harmful to newer cars. What's the best approach?
1 Answers
Paul Hadley Staff answered 2 months ago
Hello James, When it comes to checking an alternator, there are a few methods that professionals typically use:
  1. Using a Multimeter: This is the most common and safest method. Start by checking the battery voltage with the engine off; it should be around 12.6 volts. Then start the engine and check the voltage again. With the engine running, the voltage should increase to around 13.5 to 14.4 volts. This indicates that the alternator is charging the battery. If the voltage doesn't increase, or increases very little, the alternator might be faulty.
  2. Observing Warning Lights: Modern vehicles often have a battery or alternator warning light on the dashboard. If this light is on, it's a clear indication that there's a charging system issue, possibly with the alternator.
  3. Load Test: With the engine running, turn on multiple electrical accessories (headlights, AC, radio, etc.). If the voltage drops significantly (below 13 volts), it suggests the alternator may be weak or failing.
  4. Professional Diagnosis: Taking your vehicle to a professional service center like O'Reilly's or AutoZone is a reliable way to get a thorough diagnostic. They have specialized equipment to test the alternator under various conditions.
It's important to note that the old method of checking the alternator by disconnecting the negative battery cable while the engine is running is not recommended, especially on modern vehicles. This can cause voltage spikes that can damage the vehicle's electrical system, including the alternator itself. In summary, using a multimeter for a basic check and consulting a professional for a detailed diagnosis are the best approaches to determine the health of an alternator. Paul - Motor Verso Mechanics Team