7 Causes of an Alternator Not Charging (and How to Troubleshoot and Fix)
Does your car battery keep dying? The culprit could be an alternator that’s not properly charging.
Before you automatically assume your alternator is bad, let’s look at the most common causes of an alternator not charging the car battery so you can diagnose and fix these charging system issues before your car won’t start at all.
Read Also: How to Fix an Overcharging Alternator
7 Reasons Your Alternator Is Not Charging the Battery
A lot of people get confused when they begin to have electrical problems with their vehicle. It’s easy to misdiagnose these problems as being a bad battery instead of a bad alternator.
To understand the difference, you must first learn about what causes an alternator to stop charging. Then, you can inspect the vehicle and determine if the problem is your alternator.
Here are the most common causes of an alternator not charging:
#1 – Bad Alternator or Battery
Let’s start with the most obvious. Both alternators and batteries have limited lifespans. Car batteries typically last 2 to 5 years, with longevity affected by driving habits and climate. Batteries generally last longer in cooler environments.
Modern alternators usually last about 80,000 to 120,000 miles, or 5 to 8 years, though this can vary. Regular testing can help identify when these components are nearing the end of their useful life.
See Also: Code P0562 (low voltage)
#2 – Broken Belt or Pulley
The alternator relies on a belt and pulley system to convert mechanical power into electrical energy. A serpentine belt can stretch and eventually break, while the pulley can become damaged whether from an accident or normal wear and tear.
If either component fails, the alternator won’t be able to produce a charge for the battery. Regular visual inspections can help catch these issues early.
#3 – Blown Fuse
Some car models have alternators that depend on a specific fuse or fusible link to operate. These fuses can blow due to power surges or age. Once this happens, the alternator stops charging the battery.
Check your owner’s manual to locate the alternator fuse, if present, and inspect it if you’re having charging issues.
#4 – Wiring Issues
A vehicle’s electrical system includes numerous wiring components that provide power to the alternator. A disconnected or damaged wire or connecter can interrupt power generation, preventing the alternator from charging the battery.
Identifying and fixing wiring problems often requires professional diagnosis and repair. But unlike a parasitic drain which can occur almost anywhere, the wiring issue here will be more localized and easier for locate.
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#5 – Worn or Damaged Alternator Bearings
The alternator contains bearings that allow its internal components to smoothly rotate. Over time, these bearings can wear out or become damaged due to constant use, heat, and vibration.
When this happens, the alternator’s rotor may not freely spin as it should, causing increased friction and decreased efficiency. This can lead to the alternator failing to produce enough power to charge the battery effectively. You might notice a grinding or whining noise coming from the alternator area when the bearings are failing.
#6 – Faulty Voltage Regulator
The voltage regulator controls the amount of electrical output from the alternator to the battery. It helps make sure that the correct voltage is maintained, typically between 13.5 to 14.5 volts. If the voltage regulator fails, it can cause the alternator to either undercharge or overcharge the battery.
An undercharging situation will result in a battery that’s not receiving enough power, while overcharging can damage the battery and other electrical components. Many modern vehicles have the voltage regulator built into the alternator itself, while in others, it’s a separate component.
#7 – Computer Error
Almost all vehicles on the road today have a central computer system (ECU, ECM, or PCM) that manages its many subsystems and components, including the alternator.
A computer error can cause the alternator to malfunction, preventing it from charging properly. This issue will require diagnostic testing to identify and resolve. You don’t want to misdiagnose this one as having a control module replaced and reprogrammed is not an inexpensive fix.
Just pitching in to say you are a good troubleshooter. With all the garbage webpages out there that basically say “change your alternator” if it’s not charging and don’t explain why, you actually tell people what to look for to find out what is causing the problem. Kudos! 👍
My car wouldn’t start and I thought maybe something was left on in the car so the battery is dead, jump started the car and it was fine.. it happened the next day so I thought maybe it’s the battery, so I got a new battery it was fine for a week and again car wouldn’t start so I took it to a Mechanic and he said maybe it’s the Alternator got a brand new Alternator but the car is still not starting ??
Mecanic said it maybe an Electrical problem ???
You may have a parasitic draw. This means some component is still drawing power even when the vehicle is off. There is a parasitic draw test you can do to see if this is the case. Check out YouTube for a few tutorials on how to do this and see if it’s something you could try yourself. You will need a multimeter.
Hi, my car was running okay the ffg day and was charging.
This morning it’s not charging.
And if I check the plug wire where you connect to the alternator, the wires are a bit loose or broken or looks like they have been cut.
Will this cause the car not charge?
Because the battery is new, the brushes are new.
Check the alternator and battery grounds. Check the connections between the alternator and the battery. If any are corroded, they might need to be cleaned. Make sure all connections are tight as well.
You left out the stupidest reason ever: The battery light on the dash burns out. I dunno if this applies to all cars but It happened to me and I learned of other instances. I knew it was burned out but I didnt think anything so moronic could be possible: The thing that is supposed to tell you your alternator isn’t working causing it not to work.
This really happened?
Hi Sir
Your advice is very helpful especially for people like myself with limited knowledge I thank you it is much appreciated.
2004 Kia Optima. Alternator will not show more than 11 volts at the rear post. We have put in 4 different alts. Same issue. Will not charge new battery. Replaced alt belt stock with replacement but it seems small when installed. When installing belt it has to be squeezed on and then tensioned but seems to have a lot of tension arc still available on the armature device. Would a longer belt increase voltage? I am a home mechanic and have built many engines but this has me completely stumped.
It’s obvious that an alternator has internal parts strategically designed and assembled to work together in order to produce energy commonly known as electricity. The most practical way for this to happen is by spinning the pulley that is attached to the conjunction of internal parts designed to utilize friction between a copper coil windings add metal brushes. Anyway, if these parts ( bearings, starter, coil windings brushes etc.) wear and become Off canter or off center, they won’t produce enough electricity as it once did. The accessory belt might end up up stretched until it no longer makes a constant contact with every pulley. When this happens, it’s very likely for damage caused by the belt to continue until these accessories no longer function correctly. Theoretically, if the belt is tight enough to create too much force on the pulleys. This excessive force ( pressure ) can cause the bearings to become out of round. This pattern of spinning motion starts a chain reaction leading to damage that renders the alternator useless. I’m certain that the alternator relies on each revelation of the pulley to be consistent but the speed for which it turns may not matter.
Did you fix it?
How?
My car is 2011 camry all stock at 367k miles right now. Based upon the article, the alternator is way due for my car and the battery is at 3 years old. I tested the battery with engine not running at 13. With engine on, I get 13.5 . With my case, I will change the 2 most obvious first and that is either the battery or alternator. I’m doing the alternator this weekend. Oh and flashing battery light was on and off, flickering then turned off for 1 month and now acting up again but the light is now off. I hope changing my alternator (thinking it is due of old age) will give me a 14 volt reading while engine is running. I just hoping it is not no cable wiring issue.
I noticed my lights flickering and a few days later my car (06 GX 470 Lexus) wouldn’t start without jumping it off. I asked a worker at O’Reilly to check my battery and my alternator. He check the batter and it said it was a dead battery but it was reading at 12volt. (Not sure what this meant) So I bought a battery for $150. Go to work the next morning morning and at the end of the day car won’t start. So I take my car to auto shop and they put an alternator in but call me to tell me that something was wrong and it still wasn’t charging the battery so they put another one in and the same issue 😩. Now he’s saying that there is something going on where the car isn’t charging the alternator but I have already spent $550. I am so frustrated. A couple months ago I got a P2103 diagnosis reading… wonder if this has anything to do with my issue????
I don’t think the P2103 code has to do with the battery that isn’t charging. Sounds like you have a poor connection somewhere in the charging system. It could be a dirty or corroded connector to the alternator or battery, or it may be a bad ground. The shop should probably do some electrical diagnostics to see where the issue is.
The battery should read about 14 V while the car is running. If you read 14 V, drive the car around the block, park, and take another reading while the car is running. Does the voltage drop at all?
I Have Jetta 4 2l, At first my battery was not charging I took it to Auto electrical they changed the Regulator and also put new Brushes on the alternator and it was fine for some few weeks. Now it has started again it doesn’t charge to battery to 12 to 13 Voltages but it looks like is only charging the car when moving.. What can be the cause?
Please help
Assuming the battery and alternator tested good, I would check all major grounds in the charging system. Make sure they are clean, tight, and free of corrosion.
I have a 2010 Dodge Avenger sxt. The battery light came on, and two days after that, the car died on our way home from the dentist. So we jump started it twice in order to get the car home.
I replaced the alternator, and put new battery in.
Car still won’t hold charge? Every time I jump start the car, it will only run for a few sec and dies eventually. Battery light still on. Idk what to do anymore!! Help?
Check all major grounds associated with the charging system, along with the battery terminals. Make sure all are clean, tight, and free of corrosion.
I have a 1991 Nissan Sentra XE 2 door . I bought this car last year and ever since i bought it I fix 1 thing and something else f***s up. ONE WHOLE YEAR. Anyways, My car would turn off in the mornings if i didnt rev it up a good 3 times. Now my brake and my battery light on my dashboard turn on when my alternator is going at high rpms but when i slow down they turn back again… any ideas on what this could be ?
The previous owner treated it like crap and the bolts werent even from under the engine ..
It could be an issue with the alternator. I would have the alternator tested at an auto parts store. While you’re in there, check the serpentine belt tension. If the belt tension is too lose, it might be slipping at high RPM and causing the lights to come on. If the previous owner mistreated it, you could have multiple issues going on. Good luck, hope it works out for you.
I used Toyota corolla 2007 model, l cannot pack the car for a day unless l remove the positive line on the terminal just to keep power in the battery, the mechanics checked on the alternator and the battery but l finally replaced with a new battery, yet the problem persist, l want help. Thanks
It sounds like you may have a parasitic draw somewhere, possibly from the stereo or another electronic component.
2002 mercury sable 3.0 DOHC. Battery was not charging. Checked the alternator and it’s good. I found the hot wire from alternator to the outer fuse box under hood connection loose. One side of the fuse box say’s alternator, the other side battery. There is a jumper flat plate between the 2. If the connection was loose on the alternator side would this cause the battery not to charge because the jumper flat plate to the battery is loose? I did notice what looked like a flash, white splash like when a wall outlet blows on the plastic. So If the loose connection is the cause then what caused the flash. Battery tested fine with multimeter but with ac running, radio, lights the voltage dropped to 11.8 , 11.9. it should have been at 14 charging the battery. Without the load the battery is 12.4 – 12.6,
The socket where the bolt is located is somewhat melted so I can’t tighten the cable, the bolt keeps turning. So I am jb welding the bold in the socket. Hopefully that keeps it from turning and then I will put the jumper plate on and tighten the cable and test to see if the battery is charging. I am doing this to avoid putting in a new outer fuse box if I can. Not sure this will work.
Feed back and suggestions are welcomed.
Thank you
Yes, a loose connection there is probably causing low voltage and high impedance. When there is less metal contact, there is more resistance (or impedance) in the circuit. This also creates more heat.
It’s your car. If JB Weld works and you’re happy with it, that’s your call, as long as it’s not a danger to anyone else. If you ever sell the vehicle, you should disclose this type of repair to the buyer.
If it were me, I would either try to repair the threads with a Helicoil or replace the fuse box. A good Helicoil repair should hold the factory torque spec without any problems, and it also lets you use the OEM bolt. Helicoils are pretty straightforward to install if you’ve never done it before.
my 2017 ford focus 1.0 eco boost after 22,000 kilometers (2 years & 9 months with) the alternator stop working and i am very disappointed
I have a 99 Subaru Forester and autozone told me I have a bad alternator. I put the new one in and hooked up battery. It dings but I’ve noticed some new lights in the dash, a spark came out of the alternator with a pop. With new battery it seemed to be working, but weird my windshield wipers won’t shut off now and when I go to turn it over it makes that sound like when you try to start a car that’s Lready running. I had my wife start it while I was under the hood and you can hear that the sound is indeed the starter but it’s not engaging the engine.. please anyone know what is wrong?
It sounds like something isn’t grounded or hooked up properly. Here’s how I’d start.
Double check to make sure you’ve installed the alternator correctly. Next, check to see if any fuses have blown. It sounds like there is a short based on the way the wipers and starter are running.
If nothing is obviously out of place, grab a wiring diagram, a multimeter, and a test light and work backwards from the windshield wipers. You know there’s something wrong with that circuit, so seeing which systems it connects to might give you a clue as to what is shorting it out.
If this is outside your comfort zone, take it to a shop and tell them the initial problem. Then, tell them exactly what you did (step by step) with your alternator install if you can. Good luck.
Ok I just got a new starter and charged my battery up but my car still want start please tell me why
Make sure you don’t have any corrosion on the battery terminals. I’ve had a brand new battery hooked up on a car with corroded terminals and it wouldn’t even crank.