How to Tell If Voltage Regulator Is Overcharging

Warning lights can indicate a problem with the voltage regulator.

A voltage regulator is an engine component responsible for adjusting the charging voltage that the alternator produces. It is generally found on the inside or behind the alternator but can also be found elsewhere under the hood. Like all engine components, the voltage regulator can malfunction, causing the alternator to produce too little or too much voltage. Overcharging can lead to failure in the electrical system of a vehicle -- a potentially costly problem. There are several warning signs that you can look for to tell if a voltage regulator is malfunctioning and causing overcharging in your car's engine.

Things You'll Need

• Voltmeter

Instructions

1. Monitor the warning lights on your car's dashboard display. Look for lights labeled "GEN" or "ALT" indicating a potential overcharging problem with the alternator due to a failing voltage regulator. "BAT" can also indicate overcharging. These lights should turn on while the car is running.

2. Watch the voltmeter indicator on the dashboard display while the car is running. The voltmeter measures the charge coming from the alternator. Look for a voltmeter reading above 15 volts for an extended period of time, which means the voltage regulator is malfunctioning and the system is overcharging.

3. Measure the alternator charge using an external voltmeter. Connect the negative and positive leads to the corresponding leads on the car's battery while the engine is idle. Look for a reading between 13.8 and 14.2 volts for a normal charge. Higher readings indicate overcharging.

Tips & Warnings

• Check your car's owner's manual for specific voltage readings. Some engines may idle at a higher voltage (15 to 15.3 volts).

• Voltage reading should be done with all lights and accessories turned off.

• Take your car to a trained mechanic to have the charging system checked if you suspect the voltage regulator is failing.

• Wear protective gloves and eyewear when working with an engine to prevent injury.

References

• Family Car Parts: A Short Course on Charging Systems
• AA1Car; Alternator and Charging System Checks; Larry Carley