A failing alternator will cause many problems for a vehicle and will eventually result in the engine stalling or being unable to start. Testing the voltage output of the alternator is one way to detect problems with the alternator.
While the engine is idling and all electrical accessories are turned off, a properly operating alternator should produce between 13.5 and 15 volts of power. A voltage output of less than 13.5 volts may indicate a defective alternator. However, problems with the drive belt or wiring may cause reduced output as well.
The alternator drive belt should be soft and pliable to properly grip the alternator pulley. Drive belts that are hard, cracking, or show uneven wear will need replacement, and you will need to recheck the alternator voltage. The drive belt also needs to have the proper amount of tension to operate the alternator.
Problems with the alternator or battery wiring may cause a discharge that lowers the measured voltage output. Inspect wiring for looseness or damage. Battery gases often cause corrosion to the battery terminals and cables. Clean off corrosion and replace damaged cables. Recheck the alternator output after any repairs have been made.
