5 Symptoms of a Loose Alternator Belt (and Replacement Cost)

Anyone who drives a car has probably heard of an alternator before. It is responsible for sustaining the charge of the battery so that it can power the electrical components of the vehicle.

If an alternator did not exist in the vehicle, the battery would never be able to power all these electronic components for more than a short period. It simply does not generate enough energy to do this.

The alternator keeps the charge going in the battery so that the power can continue to cycle throughout the vehicle.

When an alternator is actively charging the battery, it is actually spinning inside the vehicle. There is something called an alternator belt (also called a serpentine belt) which wraps around a pulley or multiple pullies that is connected to the alternator.

The other end of the pulley wraps around the crankshaft. Therefore, the crankshaft and alternator are able to rotate together by the alternator pulley. If you didn’t have this pulley, then the alternator would not be able to do its job.

Related: Symptoms of a Broken Alternator Belt

Loose Alternator Belt Symptoms

As you continue to drive your vehicle, the alternator belt gets a little bit more worn each day. It could be susceptible to wear and tear damage or it may even come loose from the pulley. Once that happens, you can expect all kinds of symptoms to arise.

If you notice any of these symptoms, the best thing to do is have your alternator belt replaced immediately. Otherwise, you could find yourself stranded somewhere after your vehicle’s electricity shuts down.

Here are the five most common symptoms of a loose alternator belt.

1) Flickering/Dimming Lights

dim headlights

If you are driving your vehicle and suddenly notice the headlights flickering or dimming or cabin lights inside the vehicle dimming, this could mean you either have a battery or alternator issue.

When it’s a problem with the alternator belt, the flickering or dimming lights may stay consistent for quite some time before they completely go out since no power is getting to them. Depending on how old the alternator is, it can also be a sign the alternator itself is on its way out.

2) Vehicle Stalls

If your alternator belt gets too loose as you’re driving, it may cause your engine to stall. This means that you’re engine essentially shuts down and you’ll be forced to pull over onto the side of the road.

Obviously, you wouldn’t want this happening on a busy street or rush hour traffic on the highway. If this symptom is consistent with the flickering lights issue, then a loose alternator belt is more likely the cause.

3) Battery Warning Light

car battery light is on

One of the first symptoms that you should notice is the battery warning light coming on. This warning light does not always mean there is a problem with the battery itself. It could just mean there is an electrical problem in the vehicle which is impacting the battery.

Rather than wait to see what happens, you should get it checked out by a mechanic or if you’re confident, take it home and troubleshoot the issue. A loose alternator belt may be the culprit.

Related: Causes of an Alternator Going Bad

4) Chirping or Squealing Noise

noise while driving

If the serpentine belt is loose, it often results in various noises coming from your engine. With a loose belt, it doesn’t sit right up against any pullies that are rotating it so noise may occur from the friction.

You’ll often hear cars driving down the street that have this problem and it seems to occur more in colder weather. If you fail to replace your alternator/serpentine belt, the problem will only get worse and to the point that the belt may completely slip off a pulley or pieces of it start breaking off.

Related: Common Causes of Alternator Belt Noise

5) Dead Battery

dead car battery

When the alternator can no longer fully charge the battery because of a loose alternator belt, the battery will then try to provide all the power to the vehicle on its own. Unfortunately, the battery will die within minutes because it doesn’t have enough power to sustain all the vehicle’s energy needs by itself.

Alternator Belt Replacement Cost

Looking for Replacement Parts?
We recommend PartsGeek.com or BuyAutoParts.com for the best prices and selection.

serpentine belt replacement cost

The replacement cost of an alternator belt is typically between $100 and $200. The part cost is between $25 and $80 while the labor cost is between $75 and $120. The true replacement cost will depend on how long it takes the mechanic to access your alternator belt.

Related: Average Alternator Replacement Cost

Sometimes it is easy to access, so the labor will only take one hour or so. But if the belt is difficult to access, you could be looking at multiple hours of labor charges. At the most, it should not go over $300.

18 thoughts on “5 Symptoms of a Loose Alternator Belt (and Replacement Cost)”

    • In most cases, a single belt drives the alternator, water pump, A/C, etc. Even though you could technically drive for a bit with the power stored in the battery, your biggest concern would be overheating the engine which would cause catastrophic damage very quickly without a water pump. If your car has a separate belt just for the alternator, you could drive for as long as the power stored in your battery lasts (maybe 10-30 min).

      Reply
  1. Hi I’ve got a ford 01 laser glxi hatchback sedan 5 Spd manual and the battery keeps going flat and the battery is a year old can you help me

    Reply
    • Try taking your car to your local auto parts store and have them test the battery and the alternator. Many places will test them for free. If the alternator or battery are found to be bad, replace them as soon as possible. I would guess they may even put a finger on the alternator belt for you to determine if the tension is set correctly.

      Do you notice a battery light illuminate on your dash? If so, check your owner’s manual for more information on possible causes.

      Reply
    • A loose alternator belt usually sounds more like a squeal than a whistle. A whistle could potentially be caused by a leak in your air intake or maybe even gear whine from the transmission.

      Reply
  2. I just replaced the alternator on my 1999 toyota avalon. Drove it around the accelerate great but the headlights started to flicker is that a sign of the battery going bad?

    Reply
    • Hmm, hard to say. It’s possible you have a bad battery, a weak connection to the alternator, a bad connection to the headlight bulbs, or maybe a bad ground.

      Start with the simple stuff: take your car to a parts store to have the battery and alternator tested. Assuming those are good, make sure the headlights are seated securely in their housings.

      Some types of aftermarket headlights (such as LED bulbs) have different power requirements than the factory headlights, and may come with a conversion kit or adapter. If this kit was not installed or has gone bad, you may also experience flickering.

      If those don’t help, I’d also look for any loose or corroded ground straps. Make sure both battery terminals are securely tightened over the battery posts. If you notice any corrosion at the battery, clean this off with a battery terminal cleaner.

      Reply
  3. My Serpentine/Alternator belt came loose, Bluish-Green fluid came out what is that? Is there significant damage?

    Reply
    • That blue-green fluid is likely coolant by the sound of it. Check to make sure your coolant is topped off, both in the radiator and the overflow reservoir.

      That belt shouldn’t just come loose. It makes me wonder if something happened to the water pump pulley…

      Depending on your make and model, the water pump may be powered by the same belt used for the alternator. If this belt were to come off, coolant would not circulate through the engine which would lead to overheating issues, and potentially significant damage.

      You’ll need to put the belt back on before you drive so the alternator can charge the battery and coolant will flow, if indeed this belt is powering the water pump.

      In either case, I’d get it checked out by a mechanic as soon as you can.

      Reply
  4. AFTER replacing my dead/dying battery, I discovered a broken belt. And new battery dead…Im thinking the alternator .Forgot to have em check it at the autoparts store. Thanks for this article.

    Reply
  5. Bettary icon appeared on dashboard,car went off I changed alternator.. after one day again bettery icon indicated the car went off what would be the cause again?

    Reply
  6. I find the information provided here to be extremely useful.

    Thank you very much for them.

    I have a 2007 Acura MDX with very high mileage, over 200,000 miles but was running great until one evening as my wife was driving it to work, within 3/4 of a mile. It started showing battery in the dashboard with battery charging error message.

    I removed the battery and took it to auto parts store and they charged it and said it was still good battery. I didn’t want to risk driving the car there.

    I have asked a mobile mechanic to come and fix it.

    My question is whether you think the mechanic coming to fix the car will be honest with me about whether alternator belt is the issue or will he go for alternator so he can make more money?

    Sorry to sound a bit paranoid. I have been had before.

    Thank you very much for your useful advise.

    Reply
    • That doesn’t sound paranoid to me. It’s good to be cautious when you’re trusting someone else with your vehicle.

      If the mechanic has good reviews (especially from people who are mechanically inclined and check his work), it’s a safe bet that he is honest and reliable. I would rather pay more for quality work if you know the mechanic can be trusted.

      Sometimes people leave negative reviews because they don’t understand what it takes to perform a difficult diagnosis or repair. Mechanics make a decent living, but they aren’t rich; they charge what they do because they have to pay the bills.

      Diagnostics are usually the hardest part of a repair. Finding the root cause of an issue often requires a clever mind, and the troubleshooting process is something that can’t really be taught in school.

      Find a mechanic who will test instead of guess, and don’t settle for a professional parts changer. If your mechanic starts throwing parts at the problem hoping something will fix it, consider finding another mechanic.

      Reply
  7. Does the alternator outcome depend on belt fitting? Will a loose belt cause lower volts on running? Previously I used to get 14+V while running but now a days it’s below 14V. Alternator is new one.
    And if I don’t start engine for couple of days, it takes 2-3 twist to get the power.

    Reply
    • Yes, the alternator needs a properly tensioned belt in order to produce sufficient voltage, since that is how mechanical energy of rotation is converted into electrical energy. If your alternator isn’t producing enough voltage it can’t properly charge the battery, which would absolutely make it harder to start the vehicle.

      Reply

Leave a Comment