Main causes of alternator failure
It is crucial to understand the primary reasons for an alternator's failure. This part is more likely to wear out due to mechanical stress and heat, as it operates continuously from the moment the engine is turned on.
Worn-out alternator bearings
Alternators use bearings to provide a smooth rotation of the rotor shaft. Bearings wear out over time due to friction, heat, or contamination with dirt and debris.
When the bearings are worn out, they produce grinding or whining sounds originating from the engine area, creating mechanical resistance that ultimately results in alternator failure. Proper belt tensioning and regular maintenance extend bearing life.
Bad voltage regulator
The voltage regulator maintains the alternator's electrical output at a constant level, typically between 13.5 and 14.5 volts. If it is not functioning properly, the alternator will either overcharge or undercharge the battery.
Overcharging can cause the battery to overheat and shorten its lifespan, while undercharging prevents it from delivering sufficient power to the electrical components. The majority of new vehicles in India incorporate the regulator into the alternator assembly; hence, a failure typically necessitates replacing the entire alternator.
Worn alternator belt
The alternator belt (which is usually part of the serpentine belt system) powers the alternator using engine energy. Whenever the belt wears out, crumbles, or completely breaks, the alternator fails to function, and the battery warning light on the dashboard comes on.
Heat overload, oil seepage, or incorrect tension will make the belt wear out faster. At least every 40,000–50,000 km, or as specified by the manufacturer, inspection and replacement is a good idea.
| Belt Condition | Visible Signs | Recommended Action |
| Minor Cracks or Wear | Slight squealing sound | Inspect frequently |
| Frayed Edges or Slack | Slipping the alternator belt | Replace soon |
| Broken or Severely Cracked | The alternator doesn't charge | Replace immediately |
Electrical system overload
Excessive use of high-watt accessories, i.e., auxiliary lights, stereos, or second air conditioners, will overtax the alternator. Many owners install aftermarket lights or stereo systems that might exceed the battery’s recommended load. This puts additional strain on the alternator, accelerating wear and increasing the likelihood of component failure.
Loose or corroded wiring
Poor contact between components hinders the proper charging of the alternator. Loose or corroded terminals form a resistance within the circuit, resulting in a loss of voltage, and the battery light on the dashboard illuminates.
\Corrosion occurs rapidly in tropical regions due to the presence of salt and moisture in the air. That's why it is necessary to check the connections and clean the terminals properly.
Low-quality or older alternator
Remanufactured or low-quality alternators could be affordable at the time of purchase, but seldom deliver reliability. In the long run, they are also more likely to overheat, deliver low voltage output, and kill the bearings. Using OEM parts or spares from well-reputed brands can enhance the reliability.
Common signs of alternator failure
Issues with the alternator don’t appear suddenly; they often take time. There will be tiny signs, pointing towards something massive. Being aware of these symptoms can help prevent significant damage to electrical components.
Dim or flickering headlights
The power of the headlights will eventually decrease, and they might even flicker when the car is idling or accelerating. This happens because the alternator cannot supply a steady voltage, sapping the vehicle's stored battery power.
Dashboard battery warning light is on
The red warning light on the dashboard indicates that the battery is not always a battery fault. It may be that the alternator is faulty or there is a charging problem in the car. It means the alternator output is low, below normal working range, when it comes on during driving.
The car stalls or takes time to start
A faulty alternator can cause the car to stall or become reluctant while starting due to the restricted flow of current to the battery. If frequent short trips are made, the battery may not have sufficient time to charge, which can cause the car to fail to start.
Failure of electrical accessories
When power windows decelerate, dashboard lights fade, or the infotainment system reboots automatically, these are clear indications of a voltage supply instability. As these systems are directly charged by the alternator, unusual behaviour on their end is a signal that it cannot meet the electrical needs.
Squealing or grinding sounds
A whine or grinding sound from under the engine typically means worn bearings or internal alternator wear. Such noises become progressively louder under acceleration and must be investigated immediately before an alternator freeze occurs.
Dead battery or frequent jump starts
If the battery needs to be jump-started frequently, even though it is relatively new, it is most likely because the alternator is not charging it well. Jump-starting every now and then is only a short-term measure and can damage electronic control units when repeated over time.
| Symptom | Possible Cause | Action |
| Dim Headlights | Low alternator output | Check the voltage output |
| Dashboard Battery Light | Faulty charging system | Check the alternator belt and regulator |
| Car Stalling | Failure to charge the battery | Test the alternator condition |
| Frequent Jump-Starts | Faulty alternator or wiring | Check connections and the voltage regulator |
How to prevent or fix alternator failure
Preventive maintenance and regular electrical checks can significantly lengthen the alternator's life. Vehicle owners can successfully avoid or fix alternator problems by following these measures:
Check and replace the alternator if defective
If voltage output tests indicate alternator failure, replacement would be the easiest option. Have a trained technician fit it to make sure it's well-fitted and properly belt-aligned.
Inspect the voltage output (13.5–14.5V)
Check the voltage at the terminals using a multimeter. It should read between 12.6V and under load, 13.5V to 14.5V. Below this indicates undercharging, and above 15V indicates overcharging.
| Engine Condition | Expected Voltage Range | Interpretation |
| Engine Off | 12.4V – 12.8V | Normal Battery Voltage |
| Engine Idling | 13.5V – 14.5V | Alternator Working Properly |
| Engine Running Loaded | 13.2V – 14.2V | Acceptable Under Electrical Load |
| Over 15V | Overcharging | Voltage Regulator Check |
Inspect and replace the alternator belt if worn
Inspect the belt for glazing, cracks, or looseness. Replace it when noticeable wear or squealing sounds are heard during acceleration. Proper timing for belt replacement ensures that the alternator works effectively without overheating or slipping.
Clean or replace rusted wiring and terminals
Loose connections and corrosion are common yet easy causes of charging issues. Use water and baking soda to clean the terminals, and then apply petroleum jelly to protect them against further corrosion. Replace faulty or damaged wires to avoid a voltage drop.
Regularly monitor battery health
A dead battery will cause an alternator to work harder to retain the charge. Battery voltage checks and replacement every 3–4 years, and more frequently in severe conditions, minimise alternator wear.
Replace old or worn-out alternators early
The alternator remains operational but with diminished capacity. If it is used for a reasonable amount of time, the voltage starts to flicker, which can damage other electrical components of the vehicle.
Bottom line
Alternator failure is a leading cause of unexpected car breakdowns, especially in Indian cities where vehicles face heavy electrical demands and harsh climate conditions. Early signs, such as dimming headlights, dashboard warning lights, or unusual sounds, can help you catch the problem before it escalates.
Regular maintenance and timely inspections of your car’s electrical system are crucial for maintaining the health of your alternator. For a smooth and stress-free experience, choose ACKO Drive service centres.
With simple online booking via the ACKO app or the ACKO Drive website, we handle everything from doorstep pickup to a detailed inspection. Our expert technicians will ensure your car’s alternator and electrical components are in optimal condition, using only original parts to keep your car running smoothly.
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