Alternator Symptoms, Function & Replacement Cost

In Electric by Magnus Sellén1 Comment

alternatorA car without an alternator is like a home without electricity. Alternators in cars are not just used in charging your car’s battery but also to power the whole electric system of your car including the lights, stereo system, ignition, engine cooling fan, A/C’s blower, wipers, ECU etc. Earlier, DC (Direct Current) dynamo generators were used to meet and manage all your car’s electrical requirements but with the passage of time, and more scientific advancements, alternators were introduced in the 1960s.

Alternators were built to be more rugged than dynamos so less wear and tear was observed in them. Additionally, alternators proved to be more reliable and efficient in comparison to dynamos. Normally, in your car, an alternator’s shaft is connected to the engine via a belt that rotates and produces electricity to fulfil the desired result.


Alternator Symptoms

Alternators are connected to a car’s battery in linkage with the starter, ignition relay, and fuse box. There could be a variety of bad alternators symptoms, but the most common or obvious ones will be discussed below. So, the easiest way to check whether your alternator is working or not can be found below.

Battery Warning Light

If the battery light has illuminated in your dash, this could be an indication towards some fault in your vehicles charging or power system. It is a general indication, which does not usually hint towards alternator failure.

Car Starting Problem

If you parked your car in perfect working condition at night but it is causing problems in the morning the moment you’re starting it again, it means your car’s alternator is at fault and it needs to be replaced. Or else, it will discharge your car’s battery.


There is a layer of grease in your car’s alternator that helps its shaft influent rotation. While the engine runs, heat is emitted from it. This heat causes the layer of grease in the alternator’s bearings to dry out. Once, there is no grease in the alternator, you start to hear a grating noise, which damages the entire alternator.

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Battery Drains

Furthermore, if your car’s battery keeps draining even when it is in fine condition, it means your car’s alternator has failed. So, look for fluctuating lights, stopping or stalling in running engine and strange sounds while driving. All of these signs are an indication towards failing alternators.


Test/Repair A Bad Alternator

It is wise to get your car’s alternator checked annually or with the span of around 11000 to 12000 miles. Its output voltage should be precisely measured and matched with its prescribed specifications. If the output is within the prescribed range then fair enough, else get it changed before it costs you loads by damaging other things as well.

Get Alternator Tested by A Professional

As soon as the aforementioned signs start to appear, it is time to test your car’s alternator. The first thing you can do is to get your car’s alternator inspected by a mechanic. He will tell you exactly if the alternator is in a good or bad condition, or if it needs replacement. For this test, the mechanic will charge you a fee, which could be anywhere around $250-$350 depending on the make and type of your vehicle.

If you want to do it yourself, you can check the voltage of the battery with a Multimeter. When the engine is running, you should have over 14 voltage on the battery. If you get under 13 volts, the alternator charge is low. When the engine is shut off, you should have around 12 volts.

Through Light Test

This method is a bit complicated as it requires you to visually look for issues. To start off, take your car somewhere where there is no ambient light like a garage (if its daytime), switch on your headlights, and ask a friend to see whether your car’s headlamp’s intensity is fluctuating or not. Press the throttle and see if the result changes. If it does the alternator needs repairs.

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Battery Terminal Test

This test is easy in comparison to the methods mentioned above. In this test, you will need to start the engine and open up the hood. Make sure you’re wearing a pair of insulated gloves and you have a plier or spanner (of bolt’s size) around you. Proceed to undo your battery’s negative terminal. After removing the negative terminal, if your engine is still running, it means your alternator is absolutely fine and there is some other problem. But if your engine interrupts or stalls, it means your alternator is not producing ample electrical energy to keep the engine running. This method can be risky for some vehicles because the alternator can overcharge without the battery!

Observing Battery’s Condition

Bad alternators aren’t just bad for your car, but they can seriously damage your car’s battery too. This can be heartbreaking if you have just installed a fresh battery for your car. Even an inexperienced driver can detect alternator failure through these, whether his/her alternator is in a really bad position. A Bad alternator overcharges your car’s battery, which results in the battery’s wear and tear and the formation of bubbles.


Alternator Replacement Cost

A variety of alternators are available in the market depending on a number of poles, rotors, output ratings, working phenomenon, rpm (revolutions per minute), type of coil and the way it is assembled. In order to replace the alternator, firstly the battery is removed, which stops all electrical activities of your car. Its drive belt is then removed and the alternator is unmounted. Repairing an alternator is not generally preferred (due to high repairing cost), so a new alternator should preferably be installed according to factory torque specifications. A new alternator can cost you $200-$300 plus labor costs.

Its mounting should be done with extreme care as it is a very sensitive piece of equipment. And then the battery should be reconnected to the system. After inspecting the drive belt and placing it back on the pulley, the alternator’s output voltages must be measured and compared to its specified ratings. If the measured outputs are in the prescribed range, then your alternator is perfect. Otherwise, you need further changes. Battery check light is also checked, if it is still glowing it means there is still some problem, if it is not glowing, it means your problem is finished as of now.
While you are getting your alternator changed, make sure that you get your removed alternator checked first as it will ensure if your alternator is faulty or not. Especially, alternators with a bearing issue should not be repaired in any case. Your battery should also be tested to make sure that it is still in fine working condition. Make sure that electrical connections and wiring, including ground connections and all terminals, are checked and secured back and properly tightened.

  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!

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