You’re driving down the road, listening to your favorite song when, all of a sudden, the charging system warning light pops up on the dash. What does it mean? It’s just one of several symptoms that could point to a bad alternator. The symptoms of a bad alternator might also help you identify what went wrong.
Powering your vehicle’s electronics isn’t solely the job of the battery. The alternator provides the necessary electrical power whenever your car’s engine is running. Plus, the alternator charges the battery at the same time.
Alternator operation depends on a phenomenon called electromagnetic induction. When the engine is running, the drive belt turns a pulley on the alternator. That pulley causes the rotor inside the alternator to spin, which, in turn, creates a magnetic field that induces an electrical current in the alternator’s stator windings. At the same time, field current flowing through a set of slip rings creates alternating magnetic poles on the rotor.
Because the magnetic fields are alternating, the alternator produces alternating current (AC). But there’s a problem: The battery and the rest of the car’s electrical system use direct current (DC). That’s why the alternator contains diodes, which are like electrical one-way check valves, to convert AC current into DC current.
If the alternator produces too little voltage, it will not be charging the battery properly. But if it makes too much voltage, the battery and electrical system may be damaged.
A voltage regulator manages alternator output to prevent overcharging or undercharging. The regulator may be located inside the alternator, or it may be a standalone component. On many modern vehicles, a computer (often referred to as the powertrain control module) regulates charging system output.
So, what are the symptoms of a bad alternator, anyhow? These are the most common:
An alternator (or a faulty external voltage regulator) that is overcharging can cause your car’s exterior lights to be overly bright. The bulbs may also burn out more quickly than normal.
On the other hand, an alternator that is undercharging can cause your car’s exterior lights to be dimmer than normal.
A dead battery is one of the possible symptoms of a bad alternator. As mentioned earlier, the alternator charges the battery while it supplies the rest of the car with electricity. If the alternator is starting to go bad, it cannot charge the battery as efficiently. The battery then doesn’t store enough power for starting the car.
A whining or grinding sound coming from your alternator while your car is in operation is a bad sign. The noise usually indicates bad bearings inside the alternator.
Your car contains an array of electronics, all of which rely on charging system voltage. As such, a bad alternator can cause a myriad of electrical issues, especially on modern, computer-controlled vehicles.
Depending on your car, a set of warning lights in your instrument cluster can warn you of impending failures. A light you should always watch for is the charging system warning light (AKA battery light), or the bright red warning light in the shape of a rectangular car battery.
Some vehicles even have “ALT” lit when the alternator is about to fail. This serves as the most obvious warning, indicating that it’s time for you to take your car to your trusted mechanic for repairs.
Also, without a proper voltage supply from the alternator, your car’s electronics, such as computers and sensors, won’t be working correctly. This can trigger the check engine light.
Many parts of your car—including fundamentals, such as the ignition and fuel systems—won’t work right without proper charging system voltage. This means they aren’t getting enough power from the alternator. As a result, your vehicle may stall while driving.
“How do I tell if my alternator is going bad?” is a common question that can yield different answers. For one, you’re likely to have trouble starting your car.
A faulty alternator will fail to charge the battery, which means you’ll likely have a hard time starting your engine. When turning the key in the ignition, you might notice an unusual clicking noise instead of the familiar sound of your engine running.
Over time, the alternator’s drive belt can wear due to constant tension and exposure to the engine’s hot temperature. Eventually, it’ll give off a foul smell of burning rubber.
The burning smell can also come from damaged wires. When too much electricity flows through the alternator’s wires, they tend to heat up. In severe cases, they’ll burn up and emit an unpleasant odor.
When your power windows or seat warmers respond slowly, there’s a big chance that your alternator is bad. A faulty alternator won’t be able to power your vehicle’s electronics, causing some of your accessories to work intermittently. In some cases, this can even include your speedometer and other gauges on your dashboard.
Most modern vehicles are usually programmed to prioritize certain electrical systems above others, which means your powertrain control module (PCM) knows which features to turn off first. For example, your radio is likely to go out first before the headlights stop working.
Many symptoms of a bad alternator are also shared with a bad battery. Are you trying to determine whether the battery or alternator is to blame for your car problems? Here’s a quick and easy tip: try jumpstarting your vehicle. If you can jumpstart your car and it stays running, chances are, you’re dealing with a bad battery. On the other hand, if your car starts but dies shortly after, then your alternator may be faulty.
Of course, the “jumpstart” test isn’t conclusive. If you want a definitive answer as to whether your alternator is working properly, you’ll want to have it checked with a digital charging system analyzer or a carbon pile load tester.
Professional repair shops have such equipment, as do many auto parts stores. Best of all, most auto parts stores will test your charging system with the tool for free. You don’t even need to remove the alternator from your car—the tool allows for in-vehicle testing.
The best way to test the alternator is with a charging system analyzer or carbon pile tester. But you can perform a basic charging system output test (using a digital multimeter set to DC volts) at home.
To test the charging system, connect the black meter lead to the negative battery terminal and the red meter lead to the positive battery terminal. With the engine off, the battery should have a base reading of at least 12.2 volts. Otherwise, the charging system test will not be accurate.
Once you’ve determined that the battery has a proper charge, start the vehicle and increase engine speed to around 1,500-2000 RPM. If the alternator is charging, generally, the reading on your meter should be around 13.5 to 15.0 volts with all of the lights and accessories turned off.
Consult a repair manual for the exact specification for your vehicle.
A reading that falls significantly outside of that range may indicate a problem with the alternator, regulator (if the regulator is external), or battery cables. A slipped or glazed serpentine belt could also be to blame.
Here’s a helpful video to show you how it’s done:
You can also check this video to get an idea of how alternators work:
Most alternators fail due to time, miles, and use. There are, however, a few issues that can cause an alternator to fail prematurely.
Leaking fluids are a common cause of early alternator failure. Engine oil or power steering fluid dripping down onto the alternator can cause it to malfunction early on.
The way you operate your vehicle can also have an effect on your alternator. Say, for example, your vehicle spends a lot of time idling with many of the accessories (such as the lights) turned on. That can put an extra load on the alternator, causing it to create a lot of internal heat.
As a result, it may wear out prematurely.
Finally, an alternator that’s located near the bottom of the engine may be subject to water and salt intrusion. Both issues can lead to the component’s early demise.
A car can only run for a short time with a failed alternator. The alternator charges the battery when the engine is running and, once the battery is depleted, the vehicle will die and fail to restart.
Driving a car with a bad alternator can damage several electrical components, such as the fuel pump, water pump, and power steering. Damaging any of these parts can cause several systems to fail and lead to an expensive repair bill.
An alternator is designed to last the life of the vehicle—but that doesn’t always happen. In some cases, the alternator may require replacement before the car is ready for the junkyard. That usually happens somewhere between the 100,000 and 150,000-mile mark.
It’s possible to jumpstart a vehicle with a bad alternator as long as the vehicle’s battery still has some juice left. Unfortunately, once it starts, you’re running on borrowed time. As mentioned, once the battery runs out of power, your vehicle will stop running and not restart until a new alternator is put in.
If you’re handy with tools, you can replace a bad alternator. Some parts stores can even diagnose your faulty alternator while you wait at the counter.
A simple remove-and-replace operation can take a few hours though. Plus, if you aren’t confident in your abilities, you might cause more harm than good. Bring your vehicle to a professional mechanic if you want to play it safe.
Check out these videos on how to replace an alternator:
It’s best to stop driving your car until you’ve replaced the faulty alternator. Otherwise, you might have to repair or replace additional parts like the battery, which relies on the alternator to charge its depleted cells. Good thing at CarParts.com, you can easily find an alternator that fits your application.
CarParts.com understands your need for compatible parts and accessories, so we’re happy to help you find the right alternator. Plug your vehicle’s year, make, model, and engine into our website’s built-in vehicle selector, and you’ll see our direct-fit products. Once you’ve found the alternator that meets your application, you can order on your mobile device in the comfort of your home. Our professional customer service team is available 24/7, so don’t hesitate to ask about our products.
For competitively priced alternators that you can rely on, look no further than CarParts.com. View our extensive selection of alternators and enjoy significant savings when you order one today.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
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i have a 2006 PT crusier i will be going down the road and all my instrument lights will come on then go off right away this has done this has done this about 10 times the last year what could be causing this
This was very helpful. Thank you so much.
My 2011 Dodge Journey has been having some issues and my dad insists that he can fix this based off of his skills gained from youtube. He has fixed many cars before BUT he is not a mechanic so I have a hard time trusting him.
The car initially was stalling while I was driving. I was on the highway and all the electrical components stayed on but i felt the car lose power or a forward motion for about 2 seconds and then it would pick back up. It felt as if i took my foot off of the gas and then put it back down to the same speed. Then, I drove to an appointment and when I came back outside my car was dead. It wouldn't even push to start when i put my key to the ignition. I tried jumping several times and that was no good. Everything was completely dead, the lights didnt even turn on when I jumped it. My dad ended up replacing the battery which lasted all of a week. I was driving to pick up food, my car hit a small bump in the road and then the battery light came on (i've never seen this before) and on way home the radio turned off and the windows were rolling up extremely slow.
My dad said that he believes it is the alternator and after reading this, I think so too. The replacement Alternator should be arriving tomorrow. I'm going to research how to change this and if I think it is too complicated I will take it to AAA instead of accepting help from my father.
If you have an intelligent opinion on this matter, feel free to share. I could use some advisement.
When I drive my 2012 Chevy Colorado, the dash will go dead, radio everything on the dash. After that happens I put it in park, go to restart it, NOTHING. Check engine light comes on. I let the truck sit awhile and it starts back up again. Like magic? Please help
Hello
I have a mercury grand merquie it runs fine on the freeway. But just today it starts jolting or stalled acouple times. Is this a full pump issue or alternator
Good evening, I have a 2006 Cadillac STS NorthStar V8. I notice on my car dash, Low Battery Voltage came on. I soon got it home and as soon as I backed in my driveway, it completely died. At this time it was dark. I woke up the next morning, took the battery out, took it to AutoZone and they charged the battery. The battery was at 7.4. I then put it in my car and the car starting up with not problem. I decided I wanted to go for a nice evening ride. It started up, I drive it around for about 20 min, and Low Battery Voltage came on again. The car wouldn’t start so I called my wife to give me a jump. She came gave me a jump and it started. I got home while she follow me, I backed in driveway and Low battery voltage came on and car died. Is the alternator bad and needs to be replace.
Hello,
It sounds like the alternator is probably faulty. To be certain, you could take your car (if it can make it) back to the parts store and have them test the alternator. Many parts stores now have digital charging system analyzers that can test the alternator in the vehicle. The battery usually needs to be fully charged before the alternator can be tested, though.
If you have a digital multimeter (DMM) you can also do a simple charging system output test, as is noted at the bottom of this article under the "How do I test my alternator" section. Once again, the battery should be fully charged before performing this test.
I have a 2006 Ford Expedition XLT, I replaced my battery twice and the alternator but it still reads on my dash, Check Charging System with a red battery emblem. I have taken it to three different parts stores and had it tested. It doesn't bring up any codes to indicate what the problem could be. The battery and alternator test strong no problems. I have to start my vehicle at least every three days if I don't use anything electrical in it and if I do say charge my phone a number of times or whatever I have to start it first thing in the morning bec by the early afternoon I will need a jump. Is there anyone that may be able to shed some light on what the problem could be.
I'm a female so I am a little bit uneasy with going to a shop, I do know a lot about cars but when it comes to the electrical part well I'm screwed.
Hi Carolyn,
Just to clarify, you have already replaced the alternator once and that didn't fix the problem?
No
When the check engine light came on, what diagnostic trouble codes were stored? It sounds like you have a problem somewhere in the charging system circuit. You've already replaced the alternator and the battery, so, for the most part, we can rule those out.
In your vehicle, the powertrain control (PCM) controls the voltage regulator inside the alternator. There could be an issue with the PCM or there could be a problem with the wiring in the charging system. At this point, I would take the car to a professional for diagnosis. Do some research online to find a shop in your area that has a good reputation and will treat you right.
This is how the check charging system reading on my dash started, believe it or not it's the truth.
I was putting windshield washer fluid in my vehicle and the hood shocks failed and the hood slammed shut. The next morning my battery had to be jumped and continued to do this So I replaced the battery but it did no good then I replace the alternator and the check charging system reading is still there and the battery emblem also is still lit up on my dash. Now the check engine light came on about three weeks ago and I guess I will never find out what has caused either problem. The check engine light came on after I had to slam on my brakes when a vehicle pulled out in front of me, I then went and got gas and driving away from putting my gas in the check engine light came on and the only difference is when I suddenly accelerate my vehicle will act like it's flooded, or running out of gas other than that it runs fine. I just don't ever see a light at the end of the tunnel.
I have a 1996 plymouth neon and I have a few questions but I'll make it simple.
My car blows white smoke out the exhaust!
It smells bad and it dont go away but after warming up it goes away a little bit.
My car is sluggish and it dont accelerate good at all. When it is floored from a dead stop it acts weird and still has no power it has more power when it's in the manual 1st or 2nd gear its automatic but it has a 1 and 2 on the shifter.
My car wont start unless I jump it but if I charge the battery it will start without a jump for a period of time also my battery light is on in the dash
It has 206k miles and it was kind of abused but I want to keep it running a while so far It has new spark plugs and wires and new fluids and new brakes and tires. It could use an oil change but it's not bad.
I'm 20 years old I just payed 300 for this car it's my first car and no one will help me with it. I dont have the money to drop into it I can buy parts here n there but I cant afford to buy a part n it not fix anything. If someone can help please do I came to abrupt stop on fixing this car because I honestly dont know much about cars but I have a lot of common sense so feel free to text my number at 219 895 4954. Thank you!
Hi Dillan,
Unfortunately, the smoke from the exhaust and lack of power isn't a good sign. From what you describe, it sounds like an internal engine problem. You can read more about smoke from the exhaust in our article here: https://www.carparts.com/blog/white-smoke-from-exhaust/
The battery light on the dash sounds like a separate problem with the charging system.
Without seeing your car firsthand, I can't tell you exactly what's wrong or what parts you'll need. If the car is worth it to you, your best bet is to visit a repair shop for a professional, in-person assessment.
i have a Scion TC 2008 and the battery light just came on. I noticed it on the way to work as the light came on but then turned off as i drove. on the way home at night i was coming back and the light came back on. I also noticed that as i got close to home the radio and aux stopped working with the headlights on and only worked when i turned the headlights off again.does this sound like an alternator problem or a dying battery?
Hello,
I have a 1995 Jeep Grand Cherokee. It has been great to me up until recently, it would sometimes try to turn over I could hear it but it wouldn't, it would have power still just wouldn't start but it'd. I would try a few minutes later and it would start and run fine. Now there is no power whatsoever it makes no sounds no lights nothing. My first thought is the alternator, I don't have a whole lot of experience with cars my grandpa does but as he ages he isn't as capable. I think its the alternator because its no longer charging the battery / distributing power. I was considering taking it off to take it in to get tested but I don't want to waste my time with something that I don't have to do. I have a voltmeter but that wouldn't test it would it?
Something sounds like it is draining the battery when the car is off. Is there anything aftermarket on the truck? As in immobilizer, stereo etc. If so, I would start there with a multimeter.