The charging system should be inspected if:
The starting point for all charging system problems begins with the inspection of the battery, related wiring and the alternator drive belt. The battery must be in good condition and fully charged before system testing. If a Diagnostic Trouble Code (DTC) is set, diagnose and repair the cause of the trouble code first.
If equipped, the charging system warning light will illuminate if the charging voltage is either too high or too low. The warning light should illuminate when the key is turned to the ON position as a bulb check. When the alternator starts producing voltage due to the engine starting, the light should go out. A good sign of overly high voltage is lights that burn out and/or burn very brightly. Overcharging can also cause damage to the battery and electronic circuits.
Drive belts are often overlooked when diagnosing a charging system failure. Check the belt tension, check travel limit marks on the tensioner, if fitted. Check belt condition and replace the belt if needed. A loose belt will result in an undercharged battery and a no-start condition. This is especially true in wet weather conditions when moisture causes the belt to become more slippery.
If the vehicle is equipped with a voltmeter, this can sometimes give a clue to belt problems. If the indicated voltage stays low after starting, especially in wet weather, it may indicate that the belt is too loose. Other indications are indicated voltage fluctuations when loads are added or removed from the system as when turning on the air conditioner.