8 Signs Of Bad Alternator : Causes, Testing, Fixes & Replacement Cost

signs of a bad alternator2

A bad alternator in any vehicle can have many symptoms. Although the alternator is a simple-looking component in vehicles, its failure can leave your vehicle stranded on the road. Because when the engine is running, the alternator charges the battery and supplies energy to other components. But if the alternator gets damaged, then your car will run as long as there is energy in the battery, and due to a lack of charging, the battery will start draining in some time, and all the electronic functions of your car will stop working.

In this article, we will learn in detail about the main symptoms of alternator failure, how to test it, and the replacement cost.

What Is Alternator?

The alternator is a vital component in any vehicle’s electrical system, converting mechanical energy from the engine into electrical energy and supplying power to the car’s battery and electrical components.

When the alternator runs with the engine, it produces alternating current (AC), which is converted into direct current (DC) by a rectifier. This DC power generated by the alternator charges the battery and powers the electrical system, including lights, ignition, and other accessories. In fact, it plays a vital role in maintaining the electrical efficiency of the vehicle while it is running.

Signs Of A Bad Alternator

Common symptoms of a bad alternator include a dashboard warning battery light, a dead battery, dim or extremely bright lights, engine RPM instability, slow performance accessories, difficulty starting the engine or frequent stalling, growling or grinding noises, or a burning rubber smell. 

Signs of alternator failure should never be ignored. Because replacing an alternator with a new one can be more expensive than repairing it, and driving a vehicle over long distances with a bad alternator can cause damage to other electrical components and wiring. Therefore, we will know the symptoms of a bad alternator in detail so that you can solve it based on identifying its initial symptoms.

1. Dashboard Warning Battery Light


The battery indication on the dashboard is one of the main signs of a bad alternator, as it is the first indication in case of any fault in the alternator. Typically, the ECU controls every function of the vehicle, and whenever there is a mechanical or electrical fault in the vehicle, the vehicle’s ECU can continuously illuminate the light related to that fault on the dashboard. Similarly, a battery signal may show on the dashboard in case of a failure of the vehicle’s alternator or an interruption in the output supply.

2. Dead Battery

Batteries are an important component used in vehicles, without which it is absolutely impossible to start the engine of the vehicle and supply energy to other electrical components. The battery starts the engine and also supplies energy to other sensors and many other electrical components. which the battery is charged through the alternator, so that the energy storage of the battery can be kept stable.

But if there is any kind of fault in the alternator, then the alternator is not able to charge the battery, and the electrical components start taking energy directly from the battery. Due to a lack of charging, the battery starts losing its energy, and after some time, the battery becomes completely dead.

3. Dim or Overly Bright Lights


The vehicle’s lights are powered directly from the battery, and the headlights draw the most power from the battery. Because of this, an alternator is required to charge the battery while the lights are on. But if you are driving with the headlights on and the alternator is not able to charge the battery, then after some time the headlights of the car will become dim.

Dim lights in the vehicle’s headlights can also be a sign of alternator failure, and for some reasons, the lamp lights become dim or excessively bright. Which is caused by a bad voltage regulator in the alternator.

4. Engine RPM Unstable

To check the RPM of the engine in vehicles, an RPM meter is installed, which shows the reading of the crank speed of the engine. In vehicles with sensors, the RPM meter is connected to alternator power to activate operation, and when the vehicle’s alternator fails, the engine RPM meter may stop working.

In many cases, a faulty voltage regulator in the alternator may cause the alternator to constantly draw more or less charging power. This causes the engine RPM to go up or down, which can also be a sign of a bad alternator.

5. Slow Performance Accessories

windshield wipers not working

Vehicles are equipped with a variety of electronics that operate on the battery’s output power voltage, such as power window motors, wiper motors, AC/heat blower motors, radiator motors, radios, and many other electronic components. But the battery of any vehicle can provide power to all these components only for a certain period of time as per the capacity of its energy store without any charging.

But if your vehicle’s alternator fails and is unable to charge the battery, the battery will only be able to use its stored energy to operate electrical components properly for a short period of time, and as the battery weakens, the electrical components and accessories The equipment slowly starts working. As you may have noticed, when the car’s battery power is low, the power window glass moves up and down slowly.

6. Engine Difficult Starting or Frequently Stalling

As you may know, any self-start vehicle requires a battery to start. But due to a faulty alternator in the vehicle, the battery is not fully charged. Due to this, whenever you turn the key in the ignition to start the vehicle’s engine, you only hear a clicking sound instead of the rumble of the engine.

Additionally, the engine’s spark plugs are not getting enough power from the faulty alternator, which can cause your vehicle’s engine to stall or stall frequently. Due to this, a decrease in the power performance of the engine can be felt.

7. Growling or Friction Noise

Metal bushes or bearings are fitted at both ends of the alternator rotation shaft to allow the shaft to rotate smoothly without any friction or extra force in the alternator. So that there is no looseness in the rotation shaft, the winding rotor does not rub against the alternator stator, and the rotation speed of the alternator can be made smooth.

But sometimes these metal bushes or bearings can get worn out due to being too old or not being lubricated. The rotation belt may also be overtightened due to the failure of the bush and bearing. Growling noises can be made from the alternator when the alternator bearing is broken or worn out. This could also be a sign of a bad alternator.

8. Burning Smell of Rubber

The rotor and stator of the alternator have copper wires for winding. Due to this, the magnetic rotation speed is converted into electric power, and the alternator provides the electrical output supply.

But sometimes, due to shorting of the alternator windings or overheating, the varnish on the windings in the alternator and the rubber wires used start melting, causing the smell of burning rubber, which could also be a sign of a bad alternator.

How To Know If The Alternator is Bad?

If your vehicle’s alternator has gone bad, common signs you may notice include dim or flickering headlights, a warning light on the dashboard, a dead battery, a grinding or whining noise, or a sudden engine shutdown. Additionally, attention should be paid to electrical issues such as power fluctuations in accessories and difficulty starting the vehicle.

Use a multimeter to check the alternator’s voltage and ensure that a healthy alternator should maintain a voltage above 13 volts. If you experience these symptoms, they may indicate your alternator is failing. So have your vehicle inspected by a professional mechanic to confirm and resolve potential alternator problems.

What Causes An Alternator To Go Bad?

The causes of alternator failure can be wear and tear on internal components such as brushes, bearings, and diodes. Additionally, a worn drive belt, a faulty tensioner, and poor electrical connections can also impair the functioning of the alternator, affecting its performance. Finally, manufacturing defects or substandard components in the alternator can also cause premature failure of the alternator.

How To Test Alternator & Battery Voltage?

To check the voltage of the alternator, you will first need a digital voltmeter or DV (ohm) multimeter. With the help of this tool, you will be able to easily check the voltage of the alternator and battery.

Alternator & Battery Voltage Testing Process

  • To check the voltage in this process, first turn off the engine of your vehicle.
  • After that, put the red wire of the voltmeter on the positive terminal of the battery and put the black wire of the voltmeter on the negative terminal of the battery. Make sure your voltmeter is set to read DC current.
  • After connecting the voltmeter wire to both terminals of the battery, the multimeter will start showing the reading of the battery current.
  • The reading of the battery current on the voltmeter should be 12.65 volts. This reading of battery current indicates that the battery is fully charged.
  • After this, you check the voltage of the alternator. Connect the red wire of the multimeter to the positive terminal of the battery and the black wire to the negative terminal of the battery.
  • After this, you check the voltage of the alternator. Connect the red wire of the multimeter to the positive terminal of the battery and the black wire to the negative terminal of the battery, and start the engine.
  • The multimeter will show a reading of 13.5 to 14.5 volts, which will indicate that the alternator is functioning properly.

If the alternator is providing voltage from 13 to 14.5 volts after the engine is started and you are still facing a vehicle battery-related problem, then definitely your vehicle battery has gone bad, for which the battery needs to be inspected. ,

How To Fix Bad Alternator?

In case the vehicle’s alternator fails, first of all, it is mandatory to get the alternator inspected by an expert electrician. So that it can be known which part of the alternator is faulty and whether repairing or replacing which parts fixed the problem.

1. Change Worn Carbon Plate & Commutator

The copper commutator is fitted at the back end of the alternator’s rotor. On top of which the carbon in the carbon plate, while doing friction, sends the output supply of the charging current. But sometimes the carbon in the carbon plate in the alternator and the commutator are unable to remove the output of the power supply due to excessive wear. Due to this, the alternator also stops working. When this happens, the alternator can be repaired smoothly by replacing the carbon plate with a new one.

2. Change Short & Damage Alternator Rotor

The rotor rotates in the alternator, which has copper windings due to which magnetic waves generate current. But sometimes the winding of the rotor of the alternator gets shorted. Due to this, the alternator output is not able to generate charging current. For this alternator problem, you have to replace the complete rotor with a new one.

3. Change Faulty Diode Plate

Diodes are used in alternators for the process of rectifying current or converting AC current into DC. Diodes only allow electricity to flow in one direction, making it perceptible. A perfect sine wave is generated by alternating current (AC), with electricity flowing both back and forth. But sometimes the diodes in the alternator get damaged. Due to this, the output supply of the alternator gets interrupted. For this, replace the complete diode plate with a new one.

4. Change Failure Voltage Regulator

The voltage regulator in the alternator stabilizes the voltage of the DC current. and manages the supply of sufficient current for battery charging and other electrical components. But sometimes the DC voltage is too low or too high because the regulator is faulty. Due to this, problems like battery overcharging and RPM fluctuations in the vehicle start to arise. For this, the regulator of the alternator can be replaced with a new one.

5. Change Bad & Broken Bearing

The alternator has bearings on both ends of the rotor, which helps the rotor rotate smoothly. Bearings prevent friction by creating a proper distance between the rotor and the stator. But sometimes the alternator bearing breaks due to the rotation belt of the alternator being too tight, the bearing not being lubricated or the bearing getting jammed.

Due to which the rotation shaft of the alternator becomes unable to rotate. If this happens, inspect the alternator and replace the bearing with a new one if it is damaged. Because a bad bearing can damage the internal parts of the alternator, replacing alternator can be more expensive than repairing it.

6. Change Bad Stator

The stator is the main part of every type of alternator. The stator has a copper wire winding. Between which the rotation rotor rotates. But sometimes the winding gets cut short due to the alternator stator overheating, because of this, the magnetic wave is not created due to the rotation of the rotor And the alternator is unable to output the charging voltage. So if this happens, inspect the alternator and if the stator is bad, replace the alternator stator with a new one.

Alternator Repair & Replacement Cost

On average, the replacement cost of a new alternator can range from $500 to $1000, including mechanic labor.The cost of alternator repair can reach approximately $150 to $250, including the cost of mechanic labor.

Alternator repair cost largely depends on the malfunctioning alternator parts, the type of alternator, and also the vehicle model.

  • Alternator Stator Cost: $35 to $75
  • Alternator rotor cost: $75 to $125
  • Alternator Carbon Plate: $20 to $35
  • Alternator Diode Plate Cost: $19 to $30
  • Alternator Voltage Regulator: $25 to $40
  • Alternator Bearing Cost: $15 to $25


Q. How To Test Alternator?

To test the alternator, connect the red wire of the multimeter to the positive terminal of the battery and the black wire to the negative terminal of the battery. The multimeter will show a reading of 13.5 to 14.5 volts, which will indicate that the alternator is working properly. If the charging voltage is showing 13.5 to 14.5 volts more or less, So definitely the voltage regulator of the alternator is bad. which needs to be changed.

Q. How Does a Bad Alternator Sound?

AA bad alternator bearing can make a growling or friction noise.

Q What Can Damage An alternator?

The bearing, voltage regulator, carbon plate, diode plate, rotor and winding stator may be damaged in the alternator. The alternator needs to be inspected for testing.

Q. What happens when an alternator Damage while driving?

If the alternator breaks down while driving, the amount of voltage your car’s battery will store By then, your car’s electrical components will work and when the battery voltage is low, all the accessories and other electrical components of the car will start performing slowly and when the battery dies, your car’s engine and other electrical components will stop working completely.

Q. Can You Jumpstart a Car With a Bad Alternator?

In case of any car alternator failure, the car can be started by jumping it. But this is possible only if your vehicle’s battery can store some voltage. Because with a dead battery, you can jumpstart the car. But once the jumpstart wire is removed, the car will shut down again.

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