ASE A1 Engine RepairEngine Electrical Systems (General)Medium
A vehicle's charging system repeatedly causes the battery to overcharge, leading to premature battery failure. The alternator output voltage is consistently measured at 15.8 volts with the engine running. What component is MOST likely at fault?
- AHigh resistance in the charging circuit wiring
- BA faulty voltage regulator
- CA shorted alternator diode
- DA discharged battery
Show answer & explanationAnswer & explanation
Correct answer: B. A faulty voltage regulator
The voltage regulator is responsible for controlling the alternator's output voltage, typically keeping it between 13.5 and 14.5 volts. A consistent output of 15.8 volts indicates that the voltage regulator has failed and is allowing the alternator to produce excessive voltage, leading to overcharging.
Why the other options are wrong
- A. High resistance in the charging circuit wiring would cause undercharging at the battery, as voltage would drop across the resistance, not overcharging.
- C. A shorted alternator diode would typically cause undercharging or AC ripple, not consistent overcharging at 15.8V.
- D. A discharged battery would initially draw more current, but a properly functioning voltage regulator would still limit the voltage to the specified range (13.5-14.5V), not allow it to reach 15.8V.
Voltage Regulator Function
The voltage regulator maintains a stable output voltage from the alternator, preventing overcharging or undercharging of the battery.
- Typically integrated into the alternator or PCM.
- Controls the field current to the alternator rotor.
- Failure can lead to overcharging (high voltage) or undercharging (low voltage).
Memory trick: If the 'VOLTAGE' is too high, the 'REGULATOR' is the guy.