Alternator trouble can affect everything from your battery and headlights to your ability to start your car. Learn how your alternator works, the signs it may be failing, how long it can last, and how to distinguish alternator issues from battery problems.
Key Takeaways
- Common signs of a bad alternator include a battery warning light, dim or overly bright lights, a dead battery, malfunctioning accessories, starting or stalling problems, unusual noises, and burning odors.
- A failing alternator may eventually leave the battery without enough charge to start or keep your vehicle running, so don't put off having potential charging-system problems inspected.
- Battery and alternator problems can cause some of the same symptoms. Professional battery and charging-system testing can help determine which component is causing the issue.
- An alternator's lifespan can vary depending on various factors, including vehicle age, driving conditions, electrical demand, climate, and the condition of related components.
What Does An Alternator Do?
Put simply, your alternator keeps your car battery charged, allowing you to turn on your car and use electronic accessories.
Your battery provides the electrical punch needed to start the engine. In turn, the engine rotates the alternator pulley, which helps keep the battery charged while the car is running. The alternator is the bridge between these two components.
Since the battery can't keep the engine and your electrical accessories powered indefinitely, it needs the alternator to convert the engine’s rotational power into electricity. If there is any issue with this charging system, you’ll likely run into problems.
7 Signs Of a Failing Alternator
If you’re experiencing car alternator problems, you may find that your car won’t start or stay on for more than a few minutes. You might also experience battery, accessory, and light irregularities. Before any of these happens, though, you’ll likely encounter one or more of these seven bad alternator symptoms.
1. Battery Warning Light On Dash
When the battery warning light pops up on the dashboard, it’s commonly mistaken for a battery-specific issue. However, the battery warning light typically indicates a problem with your vehicle's electrical charging system, which also includes the alternator.
Alternators work at a specific voltage, typically between 13 and 14.5 volts. If your alternator fails, its voltage may drop below capacity, causing the battery warning light to appear on your dash. Similarly, the battery light may also appear if the alternator exceeds its voltage limit, depending on the level of stress it is under.
Depending on the electrical load from your car’s accessories (headlights, wipers, radio, etc.), you may see the battery warning light flicker on and off as the alternator fluctuates in and out of its intended voltage capacity. While it may seem like a minor annoyance, this light should never flicker if the alternator is in good condition and the engine is running. In this case, it’s better to bring your car in for an alternator inspection rather than end up stuck on the side of the road.
2. Dim or Overly Bright Lights
When an alternator or the alternator’s voltage regulator begins to fail, it may provide inconsistent voltage to your electronic accessories.
Generally, that takes the form of under- or over-performing equipment, such as headlights that are either too dim or too bright. You might experience flickering lights or lights that erratically switch between bright and dim. Overloaded lights can also fail prematurely, especially if the problem isn’t resolved quickly.
3. Dead Battery
Sometimes, a dead battery is just a dead battery — it’s reached the end of its life after a few years of use — or maybe the headlights were accidentally left on all night. Other times, however, a dead battery could indicate that your alternator is malfunctioning.
A bad alternator won’t sufficiently charge the battery while the engine is running, causing the battery’s charge to deplete faster than usual. One way to test whether you have a bad battery or alternator is to jump-start the car. If you jump-start your car the right way and it stays running, your battery may need replacing soon. However, if you jump-start the car and it dies again shortly after disconnecting the jumper cables, your alternator may not be charging the battery sufficiently.
If your battery only goes dead overnight or when the car is parked with the engine off, your alternator’s rectifier may be faulty. Alternators produce an alternating current (AC), but car batteries require a direct current (DC). If the rectifier is working properly, it will convert AC to DC by restricting the current to flow in one direction. But if a rectifier diode is faulty, current can flow in both directions, meaning the alternator can actually drain the battery. If the diodes in the rectifier don’t stop the electricity from flowing back, the battery will send power to the alternator when the engine is turned off, draining the car battery.
4. Slow or Malfunctioning Accessories
An alternator that isn’t supplying enough power to your car’s electronics often results in slow or non-working accessories. If you notice your windows taking longer than usual to roll up or down, or if your seat warmers feel “off,” or even if your speedometer and other instruments start going haywire while the vehicle is running, you may have an alternator problem.
Many modern vehicles also have a priority list of equipment programmed into the car that tells the onboard computer where to cut power first if the alternator isn’t supplying enough electricity. That way, if you’re driving with a failing alternator, you may lose power to your radio (or other nonessential accessories) before losing power to your headlights.
5. Trouble Starting or Frequent Stalling
Trouble starting your engine might mean your alternator isn't charging the battery. This means that when you turn the key in the ignition, all you'll hear is a clicking sound instead of the purr of your engine.
On the other hand, if your car is frequently stalling out while driving and you notice the battery light is on, it may be a sign that the control modules aren’t getting enough power from the alternator to keep the engine running.
6. Growling or Whining Noises
Cars make many odd sounds — some are harmless, while others can indicate serious mechanical problems. If you ever hear growling or whining noises coming from under the hood, you could have alternator problems or other drive belt issues, which should be checked out by a professional ASAP.
This growling or whining sound happens when the belt that turns the alternator’s pulley becomes misaligned or rubs against the side of the pulley. You may also hear this sound if the bearings that spin the rotor shaft are going bad.
7. Smell of Burning Rubber or Wires
A foul odor of burning rubber or wires could indicate that parts of your alternator are starting to wear out. Because the alternator’s drive belt is under constant tension and friction — and because it’s close to the hot engine — it may wear out over time and emit an unpleasant burning rubber smell.
Similarly, if your alternator is overworked or has frayed or damaged wires, you may smell a burning odor comparable to an electrical fire. An overworked alternator tries to push too much electricity through its wires, causing them to heat up unsafely. Damaged wires also create resistance to the flow of electricity, causing the wires to heat up and emit a foul odor.
How Long Do Alternators Last?
Unlike some components that are typically replaced at regular intervals, alternators don't have a universal replacement schedule. Depending on the vehicle and how it's driven and maintained, an alternator may continue working for much of the vehicle's life or experience problems earlier. That's why it's generally more useful to pay attention to charging-system performance and signs of trouble.
It's also important to note that a worn drive belt, weak battery, faulty wiring, or damaged or corroded electrical connections can affect the charging system's performance and may place additional strain on related components, like the alternator. Keeping up with recommended vehicle maintenance and having unusual electrical behavior checked promptly can help identify these problems before they become bigger issues.
Do You Have Battery or Alternator Issues?
Because the battery and alternator work together as part of your vehicle's electrical system, problems with either component can cause similar symptoms. A dead battery, difficulty starting, warning lights, or malfunctioning electrical accessories don't always point to one component on their own.
If you're unsure which component is responsible, read our guide to bad battery vs. alternator symptoms or visit Firestone Complete Auto Care for a professional battery and charging-system check. Testing the system can help pinpoint the source of the problem before replacing parts unnecessarily.
Get The Alternator Service You Need At Firestone
If your car's electrical system is giving you grief, it may be time to check the alternator. Firestone Complete Auto Care provides quality service that aims to keep your battery and electrical system working as they should. Schedule an appointment online or head to your nearest Firestone Complete Auto Care today for quality alternator services.
Frequently Asked Questions About Alternator Issues
Can You Drive With a Bad Alternator?
You may be able to drive briefly with a failing alternator, but it isn't recommended. If the alternator stops supplying enough power, your vehicle will begin relying on the battery's remaining charge. Once that charge is depleted, the engine may stall and may not restart. If you suspect alternator trouble, have the charging system inspected as soon as possible to avoid a breakdown.
Can a Bad Alternator Drain or Damage a Car Battery?
Yes. A failing alternator may not recharge the battery sufficiently while the engine is running, causing the battery to repeatedly discharge. Certain alternator problems, such as a faulty rectifier diode, may also allow the alternator to drain the battery while the vehicle is off. Over time, improper charging can potentially shorten the battery's lifespan.
Can You Jump-Start a Car With a Bad Alternator?
A vehicle with a bad alternator may start after a jump, but a jump-start won't fix the underlying charging-system problem. If the alternator isn't adequately recharging the battery, the vehicle may run only until the battery's remaining charge is depleted. If your car repeatedly needs a jump-start, have the battery and charging system professionally tested.
What Causes an Alternator to Go Bad?
Alternators can fail as internal components wear with age and use. Heat, moisture, or contamination, worn bearings or brushes, electrical problems, and problems with related components may also contribute to alternator trouble. Because several charging-system issues can produce similar symptoms, a professional inspection can help determine the actual cause of the problem.
