5 Causes of an Alternator Not Charging

Last Updated on April 23, 2020

The main functions of an alternator are to generate electricity for the electrical components of the vehicle and to charge its battery. The alternator produces this electrical energy by converting mechanical energy.

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If you were to try and start your vehicle without an alternator, the battery alone would not be able to produce enough power to get the engine running.

Even if you had a new car battery and were lucky enough to turn the engine over, it would probably run for about 10 minutes before the power cuts out. The alternator is necessary to keep the battery recharged and to alternate the electrical current throughout the many components of your vehicle to keep them powered.

Causes of Alternator 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.

Below are the top 5 causes of an alternator not charging:

#1 – Computer Error

ECU error

Most people are driving cars made within the last 20 years. These newer cars all have a central computer system or engine control unit (ECU) which manages and operates the vehicle’s components and parts.

This computer manages the alternator as well. Therefore, all it would take is a computer error and the result would be a malfunctioning alternator, preventing it from charging.

#2 – Broken Belt or Pulley

broken belt

The belt and pulley produce the mechanical power which gets converted into electrical energy by the alternator. Your serpentine belt can easily break if it gets stretched out too much, causing it to snap apart.

The pulley can also get damaged after a while. In either case, the alternator will no longer be able to produce a charge for the battery.

#3 – Blown Fuse

bad fuse

There are certain models of car which have alternators dependent on a particular fuse to operate. However, these fuses can blow due to a power surge or simply from old age. Once that happens, the alternator will no longer charge the battery.

Not all vehicles have these fuses, so you will have to check your owner’s manual to see if your car has them. If so, this is well worth investigating in the event your car battery is not charging properly.

#4 – Wiring Issues

alternator wiring

There are numerous wiring components in a vehicle that help produce power for the alternator. All it would take is for one wire to be disconnected or cut for power to stop being generated. As a result, the alternator won’t be able to charge the battery until the wire is repaired or replaced.

#5 – Bad Alternator or Battery

bad car battery

Alternators and batteries do not last forever, and each have their own lifespans. A car battery will last from 2 to 5 years, depending on how often you drive and the climate where you live. Batteries generally last longer in colder environments and shorter in hotter environments.

Alternators will on average last about 7 years or every 80,000 miles but there are always exceptions.

How to Fix

The most common reason for an alternator failing to charge a battery is one of them going bad. You can easily test the voltage by connecting a voltmeter to your battery while the engine is off. The voltage reading should be between 12 and 13 volts. You can automatically assume there’s a battery problem when the reading is lower.

In the event your battery’s good, start the vehicle and get the engine up to 2,000 RPM. This will put a lot more demand on the alternator.  A decreasing voltage reading on your voltmeter indicates you have an alternator problem.


130 thoughts on “5 Causes of an Alternator Not Charging”

  1. Am a technician and one Hyundai Santa Fe is having alternator problem I changed it and it’s not working I have checked the fuses and all the same what can I do?

  2. I have Toyota Yaris 1.5 2010 the alternator is not charging the battery or slow charging and all the fuse are replaced but still acting up , what can i do to sort the issue or diagnose the fault on the alternator .

  3. I have a 2006 jeep liberty and the engine light goes on just put a new alternator and battery and it start to lower the battery little what could it be

  4. I have a Honda crossroad 2007 model. One time it stopped charging and the mechanic didn’t find fault with fuses and Alternator. The only fault found was one of the cables was not supplying power to the Alternator, then he had to cut the Black and White wire and connect to another black and white wire connected to the plugs and the alternator started working. Now the check engine, VSA and another warning light are on the dash board always. After taking it for scan, The following codes appeared P0141, P1298, P0102 and 83-1 ECM/PCM relation failure. What could be the problem?

  5. 2007 Toyota Camry se 2.4 engine. I replace battery and alternator in March 2019. also replace alternator in June 2019 both rebuilt alternators. replace alternator in Sept 2019 with new not rebuilt alternator. The first 30 days or so the car start right. Now the car start slow like before. Have any ideas?

    • Run a voltage test on your battery and alternator. There might be a drain somewhere. Also, could be your starter going out.

    • I have a 2006 Scion TC. Recently, my car just died as I was driving. My dashboard lights go dim, but when I press on my brakes, all of the dashboard lights fully light up without the key in the ignition. My car won’t turn over and the lights slowly dim if I’m not pressing the brakes. My battery tested good, but my alternator was bad. I replaced my alternator, but I still have the same issue. I’m assuming it’s electrical wiring and not fuses at this point right?

    • The car’s AC should not put any additional load on the battery as long as the engine is running. Why do you suspect it’s the air conditioner?

  6. i have a 2010 transit van which had a new alternator put on but the plug that goes on the alternator is loose because the clip that holds it on snapped and im not sure what this part is called so i can get another one please help im in the uk

  7. I have a 2007 Dodge pickup diesel, i put 2 new batteries and a new alternator it drives around for a little bit then dies down, the batteries die..what could be the problem?

  8. My Iveco omnibus is idling at high revs about 1500revs I go to an iveco dealer and he said it is under charging, so my question is what might be the problem on the alternator. Can it be a regulator but the brushes are okay

  9. Hi guys my battery is being over charged and sometimes doesn’t wanna start as there is to many volts then amps. Got battery tested and battery life is 89% and battery charge is 30%. Do I have to change alternator or do diagnostic cause engine light is on? It’s a Chrysler Neon 1.6 SE 2002 model. Oh and does my alternator have a regulator or is my ECU (Computer box) suppose to regulate my battery charge? Please I need help

    • I had a similar problem to you after the alternator was replaced by myself I connected it exactly how the last one was. It turns out that some are to be connected opposite to the original. If that’s the case then it would cause you a problem like yours

  10. I have a Benz E 250 1996 model. Using new battery. While starting voltage is increasing up to12.90 volts only. While idle for 5 hours voltage reaches 12. 04 volts. Meantime alternator generating current. Do you know any fuse using for charger of e 250.

  11. I have a 1992 Lincoln town car that began (what appeared to me to begin misfiring and bogging/hesitating before finally cutting out completely.
    After having it towed back to my home the tow truck driver put a portable jumper and it started. He said the alternator was bad and not charging the battery thus not creating spark to fire the plugs.
    Long Story Short…
    I replaced both the Alternator and battery. But after doing so a handheld voltmeter pulled the same result…
    No recharging to the battery.
    Then had the New alternator tested at the auto parts store. It passed. But they gave me a second new replacement alternator just the same.
    Fuses all appear good. Nothing obvious (broken wires ect.)
    I do have some minor electrical issues, Like a short or grounding somewhere, Radio static, (more so when wipers and heat/ac is on) door locks buzz occasionally when pressed,
    No funds to have it brought to a garage and I have no clue or idea how to trouble shoot this problem.
    Please advise, any feedback/assistance is much appreciated and warmly welcomed.
    Thank you.

    • This sounds like a grounding issue. Make sure the battery terminals and posts are really clean. Get a battery terminal cleaner if you don’t have one and clean off any corrosion. Corrosion around the battery often appears white, but could also look like rust. Make sure you disconnect both ends of the battery when you do this (disconnect the negative terminal first).

      Check all your ground straps to make sure they look clean. A loose or dirty ground strap could cause a plethora of seemingly unrelated electrical issues.

      Additionally, I would look at the wiring harness in the engine bay (particularly around the connectors) to make sure no wires are severed or have exposed insulation. Sometimes these wires get brittle with age, especially in hot areas.

      Sometimes the simplest failures cause the largest issues. Good luck on your search.

  12. My AC technician replaced my Toyota Sienna 2000 Condenser and Compressor. After the replacement the battery won’t charge when the AC is on, until I switched it off. Now I drove for about 30 minutes with the headlight on, I packed to pick up some items then return to switch the car on then discovered the battery is totally flat. All these happen the same day, after I picked the car from the technicians shop.

    Please what could be wrong?

  13. I have a classic old school corvette with factory stock amp meter with needle that will go to. Charge or discharge only problem I have is I have never seen the ammeter needle go to charge? Even at higher engine rpm however the needle will jump to discharge when I turn on my headlights I do have a new high amp alternator but shouldn’t it go to charge when engine is going down the freeway or turning a higher rpm? Thanks for your input

  14. Alternators use the mechanical power of a belt and pulley to generate the electrical energy for the vehicle. The problem is that the alternator belt and pulleys are not too durable, which means they can easily break.

  15. Good afternoon, my car is 1999 Toyota sienna, I bought my battery 2yrs ago but recently if I want to ignite my car it’s struggled to answer and later it was showing battery on the dash board. I recharge my battery and yet the battery got low within some minutes. I call on technician he said i should change the alternator capacitor and cut-out. Please can I go ahead.

  16. 2000 Jeep Cherokee
    Meter on dash board shows a slight discharge, adding a load (lights, A/C, radio, turn signals) the discharge gets greater. At first I just thought it was a bad battery so I replaced it. Took about 2 months and the battery started to loose charge. Replaced the alternator and the symptoms are still the same. Slight discharge without any load. Any ideas?

    • It sounds like you may have a parasitic draw. Do a quick google search on how to test for a parasitic draw and see if that helps you find the problem. You will need a multimeter for this test.

    • 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.

  17. 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.

  18. 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

  19. 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.

  20. 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

  21. 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.

  22. 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.

  23. 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.


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