What does a voltage reading lower than normal from an alternator indicate?

A voltage reading lower than normal from an alternator indicates that the alternator may be failing. Normally, an alternator is responsible for charging the battery and providing power to the electrical systems of the vehicle while the engine is running. A properly functioning alternator typically outputs a voltage range between 13.5 to 14.5 volts. When the voltage reading falls below this range, it suggests that the alternator is not generating sufficient power to keep the battery charged or support the electrical loads of the vehicle. This could be due to several issues, such as worn out brushes, a failing voltage regulator, or a defective winding in the alternator itself, signaling that maintenance or replacement may be necessary.

In contrast, a fully charged battery would show a higher voltage with the engine off but would not be indicated by the alternator's voltage output, and a healthy alternator would provide adequate voltage. Both a properly functioning alternator and a properly idling engine are not directly related to low voltage readings, as they would typically support normal or elevated voltage levels.