6 Signs Your Alternator Might Be Failing

Battery warning light on This is one of the easiest signs to notice. Your car's battery is equipped with a sensor that detects current levels. If the charge drops below a certain threshold, the sensor triggers the warning light on your dashboard.

• A low battery often signals an issue with the charging system, but it doesn’t automatically mean you need a new battery or alternator. Sometimes, it's just a faulty sensor.
• If you see the warning light, it’s important to address the issue promptly to avoid being stranded on the road.

Car struggles to start One of the most obvious signs of a failing charging system is difficulty starting your car or needing to jump-start it repeatedly. If the car takes multiple attempts to start or you hear a clicking noise when turning the ignition, it could mean the battery is dead—and the alternator is failing. While the battery powers the engine to start, the alternator keeps the car running once the engine is on. If the alternator isn’t working correctly, the system borrows power from the battery.

• This sometimes happens when both the alternator and battery are functioning, but the alternator can’t replenish the borrowed power while the car is running.

Engine stalls If your vehicle stalls while driving, it could be a sign that the electrical system has been relying on the battery rather than the alternator. As the battery depletes, the car will stall out.

• If your car has a battery-saver feature, the battery light will illuminate, and you may notice the air conditioning and radio turn off to conserve power before the engine stalls.

Headlights are dim or too bright If your headlights or other electrical accessories seem unusually dim or bright, it could be a sign that your alternator is failing to provide a stable power supply. You may also notice flickering lights or lights that randomly switch between bright and dim.

• This inconsistent power supply can also shorten the lifespan of your headlights, as it places additional stress on the lighting elements.

Unusual sounds from under the hood If you hear whining, growling, or screeching sounds after starting your vehicle, it typically indicates an issue with the belt, such as misalignment or wear. However, it could also be due to damaged bearings in the alternator’s rotor. Whether it's the belt or the bearings, it's important to have the issue looked at by a professional to avoid a breakdown.

Smell of burning rubber or wires A worn alternator belt often gives off a burnt rubber odor as it becomes loose or misaligned and rubs against hot engine parts. Likewise, frayed or damaged alternator wires can emit a smell similar to that of an electrical fire.

• If the alternator struggles, it may force excessive electricity through the wires, causing them to overheat and produce a distinct odor.

Examine the alternator or serpentine belt for damage. One of the most common causes of alternator issues is a worn or misaligned belt. Start by inspecting the alternator belt located on the engine's opposite side of the battery. Look for signs of cracking, fraying, or missing sections.

• Older vehicles might have a separate belt for the alternator, while newer models feature a serpentine belt that drives the alternator, power steering, air conditioning, and more.
• If the car is running, inspect the belt while the engine is on to check its full length. If not, use a flashlight to examine it more closely.

Use a voltmeter to test the alternator. With the engine off, connect a voltmeter to the battery terminals to check the flow of current between the alternator and battery. Start by checking the battery’s voltage—it should be close to 12.6 volts. Once the voltmeter is connected, start the car and rev the engine to around 2,000 RPM to activate the alternator, then test the battery again with the engine running.

• If the alternator is in good condition, the voltage reading should be between 14.2 and 14.7 volts.
• If the pre-engine-start voltage is below 12.2 volts, charge the battery with an automotive battery charger before retesting the alternator.

Visit a mechanic or auto parts store for testing. If you’re not confident in testing your car’s battery charging system yourself, it’s a good idea to take it to a mechanic or an auto parts store. Many places will test your alternator and battery for free. If your vehicle won’t start, it’s best to take it directly to a mechanic to avoid multiple tows, as auto parts stores typically don’t handle repairs.

Replace a damaged or worn alternator or serpentine belt. If the alternator or serpentine belt is cracked, frayed, or broken, you can either replace it yourself or have a mechanic do the job if you're not comfortable with the repair. The cost of replacing these belts generally runs around $200, depending on your vehicle’s make, model, and location.

Fix or replace a malfunctioning alternator. If the alternator is the issue, you might be able to repair it (or do it yourself), depending on the damage and cause of failure. However, replacing the alternator is often the better choice to prevent future breakdowns.

• The cost for a mechanic to replace an alternator generally ranges between $200 and $600, including parts and labor.

Car won’t start Start by jumpstarting your vehicle. If the car fires up and runs smoothly, your battery may be the culprit. Once the engine is running, shut it off briefly and attempt to start the car again. If it fails to start, it's time to replace the battery.

Dim or flickering lights A weak battery struggles to hold a charge. If you turn on the headlights while the car is off, it will drain the battery quickly, causing the headlights, taillights, and even dashboard lights to flicker or dim.

Corroded, swollen, or cracked battery If you notice a powdery substance around your battery’s terminals, it’s a sign of leakage. This is a common indication that the battery needs to be replaced. You can clean the corrosion using a wire brush, warm water, and baking soda, which can prolong the battery's life until you replace it.

• If the battery is swollen, replace it immediately, as swollen batteries can explode, making it dangerous to handle on your own. In such cases, it's safer to tow the car to a mechanic.
• The average cost for a mechanic to replace your car's battery ranges from $362 to $373.

A battery older than 3-5 years Car batteries typically last between 3 and 5 years with normal use. If your battery exceeds this age and you're noticing issues with your car's battery charging system, it’s likely time for a replacement.

Can your car run with a bad alternator? Yes, but not for long. If the alternator is malfunctioning, the battery will have to power the car while it’s running, which depletes its charge quickly. A failing alternator, if still working, could overcharge the battery, potentially requiring both the alternator and battery to be replaced. Additionally, there's a higher chance of your car stalling while driving.

• While it’s typically safe to drive with a failing alternator, you risk getting stranded if it fully stops working and the battery dies.

Can you jumpstart a car with a bad alternator? You may manage to start a car with a bad alternator using a jumpstart, but once the initial power from the jump runs out, the car will stall again, as the alternator cannot keep the car running.

• Jumpstarting a car with a bad alternator might also damage the electrical components due to potential voltage spikes.

Will a bad alternator drain a battery when the car is off? In very rare instances, issues with the alternator diodes could cause a parasitic drain on the battery. However, it’s more common for a failing alternator to indirectly lead to a battery draining while the car is running.

What makes alternators go bad? Typically, an alternator lasts between 7 and 10 years. Over time, regular use can cause wear and tear, eventually leading to failure. Leaks from engine or power steering fluid onto the alternator can also accelerate damage, reducing its lifespan.

• If the alternator is positioned at the bottom of the engine, road salt and water exposure could also contribute to its deterioration.

• Before testing the alternator or battery with a voltmeter, make sure the car is switched off.
• Be sure to turn off and unplug your battery charger before using it to charge the battery.
• Always wear safety goggles and insulated gloves when handling the car battery.
• When jumpstarting a vehicle, avoid allowing the positive and negative jumper cables to touch when they are connected to the battery.
• Secure long hair, loose clothing, and jewelry before working under the hood with the engine running.