What are the faults of the generator and is it difficult to determine them?

An alternator is a vital component of your car's electrical system. It is not often mentioned, but it is responsible for charging the battery, and feeds all power consumers during engine operation. Starting from headlights, windscreen wipers and on-board electronics. Without a good generator, the battery will run out quickly, and important systems can fail. As a result, this may put you in a challenging situation. As electronics in cars improve, the role of the generator becomes even more significant. Unfortunately, diagnosing alternator failures can be difficult, as the symptoms typically overlap with other electrical problems, especially those related to the battery or wiring.

Let’s explore the most common alternator faults, what causes an alternator to go bad, and how to diagnose alternator problems effectively.

The role of the alternator and its connection to the battery

The alternator works hand in hand with the battery. When the engine is running, the alternator generates electricity to power all devices and recharge the battery. If either component fails, the entire system is disrupted. That’s why accurate alternator troubleshooting is essential to avoid false assumptions.

Pulley

The pulley connects the alternator to the crankshaft via the serpentine belt.

🔸 Common issues: worn-out grooves, jamming, or slippage. A damaged pulley causes unstable rotation, which increases bearing load and reduces alternator lifespan.
🔸 Causes: improper belt tension (either too loose or too tight), poor installation, or material fatigue.
✔️  Diagnosis & Fix: Inspect the pulley for visible wear and test belt tension manually or with a gauge. Listen for squealing noises. Adjust or replace as needed. Preventive inspection every 30,000–40,000 km is advisable.

Front Bearing (Hollow Disk)

The bearing allows the rotor to spin smoothly.

🔸 Common issues: abrasion, noise (whining or grinding), and vibration.
🔸 Causes: prolonged use, contaminated grease, or excessive belt tension.
✔️ Diagnosis & Fix: Use a mechanic’s stethoscope while the engine is running. If noise intensifies when the alternator is under load (e.g., lights on), replace the bearing.

Rotor Wheel

The rotor is the rotating part of the alternator and is key to magnetic field generation.

🔸 Common issues: broken or shorted winding, unbalanced rotation, or jamming due to internal damage.
🔸 Causes: high mileage, voltage surges, or exposure to water.
✔️ Diagnosis & Fix: Check winding resistance with a multimeter in Ohm mode. Normal resistance is between 1.8–5 Ohms. A value outside this range indicates damage. In such cases, the rotor must be rewound or replaced.

Understanding what causes an alternator to go bad starts with recognizing how mechanical stress and electrical degradation interact.

Rear Bearing (Distance Collar)

Though similar to the front bearing, this part is more exposed to temperature changes from the rectifier.

🔸 Common issues: wear-induced imbalance, humming sounds, or sudden jamming.
✔️ Diagnosis & Fix: Inspect during alternator disassembly. Replace when wear or play is detected.

Brush Holder

The brushes transmit current to the spinning rotor through contact with slip rings.

🔸 Common issues: voltage drops, poor current delivery, intermittent charging.
🔸 Causes: brush wear, dust buildup, corrosion, or spring failure.
✔️ Diagnosis & Fix: Measure charging voltage under full load. If below 13.1V, inspect the brushes. Clean the area with electrical contact cleaner and replace brushes if worn under 5 mm.

This step is often overlooked but essential when learning how to diagnose alternator problems properly.

Diode Set (Rectifier)

This block converts the alternating current (AC) into direct current (DC).

🔸 Common issues: diodes burn out or short-circuit, causing battery drain or undercharging.
🔸 Causes: overheating, surge voltage, or water entry.
✔️ Diagnosis & Fix: Use a multimeter in diode test mode. If current flows both ways, the diode is faulty. Replace the diode set as needed.

Ignoring this can be fatal for the alternator and is a prime example of what causes an alternator to go bad over time.

Voltage Regulator

Responsible for maintaining a constant voltage, typically around 13.8–14.5V.

🔸 Common issues: overcharging (boiling battery), undercharging (dim lights), or fluctuating voltage.
🔸 Causes: low-quality replacement parts, internal failure due to heat or corrosion.
✔️ Diagnosis & Fix: Monitor system voltage with a multimeter. Replace the regulator if readings deviate under standard load conditions. Use quality components to avoid repeated failures.

Starter-Related Function

In certain vehicle configurations, the alternator works in close loop with the starter’s electrical pathway.

🔸 Common issues: coil degradation, weak charging.
🔸 Causes: road salt, engine washing, or general moisture.
✔️ Diagnosis & Fix: Use a megohmmeter to test insulation. Replace damaged winding coils or the complete starter unit.

Rear Cover and Brush Cover

These provide protection and structural support.

🔸 Common issues: cracked plastic, broken mounts, clogged ventilation holes.
🔸 Causes: age, vibration, or mechanical impact.
✔️ Diagnosis & Fix: Inspect for physical damage during maintenance. Replace damaged covers to ensure proper airflow and prevent overheating.

Hardware and Mounting

Even bolts and brackets matter.

🔸 Common issues: misalignment, excessive vibration, cracked housings.
🔸 Causes: poor installation, rough roads, engine torque.
✔️ Diagnosis & Fix: Check tightness of all fasteners and ensure the alternator is mounted with minimal stress. Misalignment can prematurely wear out belts and bearings.

Prevention and maintenance tips

To avoid sudden alternator failure, it’s important to follow several preventive maintenance practices. Regularly inspect belts and wiring approximately every 10,000–15,000 km to ensure proper tension and the absence of cracks or fraying. Pay close attention to unusual noises—especially whining, squealing, or buzzing—which often appear under electrical load and may indicate early alternator issues. Keeping the engine bay clean is equally important; however, avoid pressure-washing the alternator to prevent water ingress that can lead to short circuits or corrosion. When replacing components like brushes, diodes, or voltage regulators, always opt for high-quality parts to ensure long-term reliability. Lastly, performing a comprehensive alternator diagnostic test every 40,000–50,000 km—particularly before long journeys or during seasonal changes—can help detect hidden problems early and prevent unexpected breakdowns.

Conclusion

Proper alternator troubleshooting involves both mechanical and electrical testing. While some issues like pulley noise or low voltage may be easy to spot, others require multimeter tests or professional equipment. Knowing how to diagnose alternator problems early helps prevent cascading failures that may affect the battery, starter, or even the car's ECU.

Ultimately, understanding what causes an alternator to go bad—from worn bearings to electrical shorts—empowers car owners to stay ahead of costly breakdowns. Regular checks, timely repairs, and attention to signs like flickering headlights or strange engine sounds can save you from being stranded on the road.

Need help interpreting test results? inCarDoc offers smart tools to monitor your car’s alternator status in real time