Signs of a Bad or Failing Alternator

The alternator is a vital part of your car’s electrical system. Think of it as the main generator that keeps everything running when your engine is on. Not only does it recharge your car’s battery after you start the engine, but it also supplies all the electrical power your car needs while you’re driving – for lights, radio, wipers, air conditioning, and all the onboard computers. Without a working alternator, your car will run solely on battery power, which will quickly drain, causing your vehicle to stop.

When an alternator starts to fail or completely dies, your car will usually give you clear warnings.

Specific Signs of a Bad or Failing Alternator

When your alternator isn’t doing its job, you’ll notice problems related to your car’s electrical power:

1. Dashboard Warning Lights:
   • “CHARGE” or “BATTERY” Light: This is the most common and direct indicator. A light shaped like a battery (often red) or sometimes just the word “CHARGE” will illuminate on your dashboard. This means the system isn’t charging the battery properly.
   • Check Engine Light (CEL): On many modern vehicles, a failing alternator (especially if it’s undercharging or overcharging) can trigger the Check Engine Light, indicating an electrical system fault.
   • ABS, Traction Control, or Other Lights: Because other systems rely on a stable electrical supply, a dying alternator can sometimes cause seemingly unrelated warning lights to come on due to low voltage or electrical interference.
2. Dimming or Flickering Lights:
   • Your headlights might appear dim, especially at idle, and get brighter when you rev the engine.
   • Your dashboard lights might dim or flicker.
   • Interior lights and radio displays may also behave erratically. This happens because the alternator isn’t consistently providing enough power, and the battery is struggling to keep up.
3. Electrical Component Malfunctions:
   • Your radio might cut out or have static.
   • Power windows might move very slowly.
   • The power seats might struggle.
   • Essentially, anything that uses electricity might not work correctly or at all. This is a clear sign the alternator isn’t supplying enough juice.
4. Problems Starting the Vehicle / Repeated Dead Battery:
   • If your alternator isn’t charging the battery, the battery will eventually die. You’ll then find your car hard to start, or it may not start at all, just making a clicking noise when you turn the key.
   • You might find yourself needing to jump-start your car repeatedly because the battery keeps running down, only for the car to die again shortly after being driven.
5. Engine Stalls While Driving:
   • If the alternator completely gives up while you’re driving, the engine will eventually stall. This happens because the engine’s ignition system and fuel pump (and all other vital electronics) stop receiving power once the battery runs out.
6. Abnormal Noises from the Engine Area:
   • You might hear a high-pitched whining or growling sound coming from the front of the engine, usually near the serpentine belt. This noise often gets louder as you rev the engine. This usually indicates that the bearings inside the alternator are failing and need replacement.
   • A loose or worn serpentine belt (which drives the alternator) can also cause squealing noises, and a slipping belt means the alternator isn’t being spun fast enough to charge properly.

Understanding Why Alternators Fail

Alternators can fail in a few different ways:

1. Undercharging: This is the most common type of failure. The alternator simply isn’t producing enough electrical current. This leads to dimming lights, a constantly discharged battery, and eventually, the car stalling. On modern cars, it can also cause complex issues with the vehicle’s onboard computers and electronics due to low voltage.
2. Overcharging: While less common, an alternator can also produce too much voltage. This can quickly damage your battery, causing it to overheat and fail, and significantly shorten the life of light bulbs and other electronic components in your car. On modern vehicles, overcharging can also trigger the Check Engine Light and cause havoc with electrical systems.
3. Bearing Noises: Sometimes, the electrical parts of an alternator work fine, but the bearings (internal components that allow the rotor to spin smoothly) start to wear out. This causes that high-pitched whirring or grinding noise. While the alternator still charges for a while, the bearing noise is a strong indicator that it’s on its way out.

How to Diagnose and Fix an Alternator Problem

Diagnosing an alternator problem can be relatively straightforward, but requires the right tools:

• Voltage Test: A mechanic can use a digital multimeter at your battery terminals. With the engine running (and lights off), a healthy alternator should typically show a charging voltage of around 13.8 to 14.2 volts (this can vary slightly by vehicle).
• Amperage Output Test: More advanced testing involves checking the alternator’s amperage output under an electrical load (e.g., turning on headlights, radio, AC). This is done using an inductive probe around the battery wire.
• Dedicated Charging/Starting System Tester: This is the easiest and most reliable method. Most repair shops and even some auto parts stores have specialized tools that can quickly and accurately test your entire charging and starting system with just a few button presses.

Before condemning the alternator itself, a mechanic will always check a few other things:

• Drive Belt: Ensure the serpentine belt that drives the alternator is tight and in good condition. A slipping or loose belt means the alternator isn’t spinning fast enough to charge properly.
• Battery Condition: A thoroughly dead or internally shorted battery can sometimes trick the alternator into overcharging or simply fail to hold a charge, making it seem like an alternator problem when it’s primarily the battery. Always ensure the battery is charged and healthy first.

In the past, alternators were often repaired or rebuilt. However, given their relatively inexpensive cost now, most repair facilities will simply replace the entire alternator with a new or remanufactured unit if it’s found to be faulty.