Alternator Symptoms, Function & Replacement Cost

In Electric by Magnus Sellén1 Comment


A car without an alternator is like a house without electricity. Alternators in cars are not only used to charge the car battery, but also to power the entire electrical system of your car, including lights, stereo, ignition, engine cooling fan, air conditioning fan, windshield wipers, ECU, etc. In the past, DC dynamo generators were used to meet and manage all the electrical requirements of your car, but over time and with further scientific advances, generators were introduced in the 1960’s.

These generators were built more robustly than dynamos, so there was less wear and tear on them. Alternators also proved to be more reliable and efficient compared to dynamos. Normally the shaft of an alternator in your car is connected to the engine via a belt, which rotates and generates electricity to achieve the desired result.

Alternator Symptoms

Alternators are connected to the car battery in connection with the starter, the ignition relay and the fuse box. There could be a variety of symptoms for bad alternators, but the most common or obvious are discussed below. The easiest ways to check whether your alternator is working or not are given below.

Battery Warning Light

If the battery indicator in your dashboard lights up, this could be an indication of a fault in your vehicle’s charging or power supply system. This is a general indication and does not normally indicate an alternator failure.

Car Starting Problem

If you have parked your car at night in perfect working order, but it presents problems in the morning when you start it again, it means that the alternator of your car is defective and needs to be replaced. Otherwise, the battery of your car will be discharged.


There is a layer of grease in the alternator of your car which supports the rotation of the shaft. While the engine is running, heat is emitted from it. This heat causes the layer of grease in the alternator bearings to dry out. As soon as there is no more grease in the alternator, you will hear a crunching sound that damages the entire alternator.

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Battery Drains

If the battery of your car is continually drained, even if it is in good condition, this also means that the alternator of your car has failed. So watch out for fluctuating lights, stopping or stalling with the engine running and strange noises while driving. All these signs indicate that the alternator has failed.

Test/Repair A Bad Alternator

It is advisable to have your car’s alternator checked annually or when the range is about 11000 to 12000 miles. Its output voltage should be accurately measured and adjusted to the prescribed specifications. If the output power is within the prescribed range, then it is fair enough, otherwise, have it changed before it costs you loads by damaging other things as well.

Get Alternator Tested by A Professional

As soon as the above-mentioned signs appear, it is time to test the alternator of your car. The first thing you can do is to have your car’s alternator checked by a mechanic. He will tell you exactly if the alternator is in good or bad condition or if it needs to be replaced. For this test, the mechanic will charge you a fee that can range from $250 to $350 depending on the make and type of your car.

If you want to do the test yourself, you can check the battery voltage with a multimeter. When the engine is running, the battery voltage should be above 14. If you get below 13 volts, the charge of the alternator is low. When the engine is switched off, you should have about 12 volts.

Thorough Light Test

This method is somewhat complicated because it requires a visual search for problems. To begin, take your car somewhere where there is no ambient light, such as a garage (if it is daytime), turn on your headlights, and ask a friend to see if the intensity of your car’s headlights varies or not. Press the accelerator pedal and see if the result changes. If it does, the alternator needs to be repaired.

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Battery Terminal Test

This test is simple in comparison to the methods mentioned above. For this test, you have to start the engine and open the bonnet. Make sure you are wearing a pair of insulating gloves and have pliers or a wrench (bolt size) around you. Next, disconnect the negative terminal of your battery. If your engine is still running after removing the negative pole, this means that your alternator is perfectly fine and that there is another problem. However, if your engine stops or stalls, it means that your alternator is not producing enough electrical energy to keep the engine running. This method can be risky for some vehicles as the alternator can be overcharged without the battery!

Observing Battery’s Condition

Bad alternators are not only bad for your car, but they can also seriously damage the car battery. This can be heartbreaking if you have just installed a new battery for your car. Even an inexperienced driver can detect an alternator failure in this way. A bad alternator overcharges the car’s battery, which causes the battery to wear and the formation of bubbles.

Alternator Replacement Cost

Depending on the number of poles, the rotors, the output power, the operating phenomenon, the speed (revolutions per minute), the type of coil and the type of assembly, different generators are available on the market. To replace the alternator, the battery is first removed, which stops all electrical activity in your car. Then the drive belt is removed and the alternator is removed. Repairing an alternator is generally not preferred (because of the high repair costs), so a new alternator should preferably be installed according to the factory torque specifications. A new alternator can cost you $200-$300 plus labor costs.

Its installation should be done with extreme care as it is a very sensitive device. And then the battery should be reconnected to the system. After the drive belt is checked and put back on the pulley, the alternator output voltages must be measured and compared to the specified values. If the measured output voltages are within the specified range, then your alternator is perfect. Otherwise, further modifications are necessary. The battery indicator light also needs to be checked; if it is still lit, this means that there is still a problem; if it is not lit, this means that your problem is now over.

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If you have your alternator replaced, first have your removed alternator checked, as this will determine whether your alternator is faulty or not. Especially alternators with a storage problem should never be repaired. Your battery should also be tested to ensure that it is still in good working order. Make sure that the electrical connections and wiring, including the earth connections and all terminals, are checked and reattached and properly tightened.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

1 thought on “ Alternator Symptoms, Function & Replacement Cost ”

  1. My battery seems to drain faster these days. I haven’t taken the car to the auto repair shop yet. At least now I have an idea on where they can start. Thanks!

  2. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
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