How to Determine If an Alternator Is Failing While the Vehicle Is Running and Checking Its Output Voltage

Alternators are crucial components in vehicles, responsible for generating electrical power to keep the vehicle running. A failing alternator can lead to serious issues, such as dim dashboard and headlight lights, which might compromise your driving experience. In this article, we will discuss how to determine if an alternator is failing while the vehicle is running and the process for checking its output voltage.

Symptoms of a Failing Alternator

When an alternator is failing, it often manifests with clear symptoms. The first and most noticeable sign is dim dashboard and headlight lights. This is a direct indication that the alternator is not producing enough power to keep the electrical system running effectively. Other common symptoms include the dashboard warning lights coming on, especially the one that signals a low voltage issue.

Checking the Alternator's Output Voltage

Determining whether the alternator is failing involves checking its output voltage. This can be easily done using a multimeter, a device that can measure voltage, current, and resistance. Here’s a step-by-step guide on how to do this:

First, ensure that your vehicle is running. Set your multimeter to measure DC volts (DCV). Use the 200V range for this measurement. Find the battery terminals. The positive terminal is typically marked with a ' ' symbol, while the negative terminal is usually marked with a '-' symbol. Connect the black probe of the multimeter to the negative terminal of the battery. Connect the red probe to the positive terminal of the battery. Read the voltage displayed on your multimeter.

A healthy alternator should keep the battery voltage around 14.4 volts when the engine is running. If the reading is consistently below 13.5 volts, it indicates that the alternator is no longer functioning properly and needs to be replaced.

Additional Methods to Check Alternator Output Voltage

For those who prefer easier methods, there are several built-in solutions in modern vehicles. Many cars come with a built-in multimeter at the cigarette lighter socket. These devices can give a quick read on the battery voltage while driving. A healthy car should show around 14.3 volts with the engine running. When the car is off after sitting for 30 minutes, a fully charged battery should read around 12.6 volts.

For more detailed diagnostics, you can invest in a portable OBDII adapter. These devices connect to your car's onboard diagnostic port and can provide a wealth of information about the vehicle's electrical systems, including the alternator. This can be particularly useful for diagnosing issues and verifying the health of the alternator.

Professional Diagnosis

If you are unsure about your vehicle's alternator, the best course of action is to consult a professional. An auto electrician can test both the alternator and the battery while you are present. They can provide a comprehensive diagnosis and recommend the best course of action based on their findings.

In conclusion, understanding the signs of a failing alternator and knowing how to check its output voltage is crucial for maintaining a safe and reliable vehicle. Whether you choose to use a multimeter or a built-in system, staying vigilant can help prevent serious issues down the line.