ASE G1 Auto Maintenance and Light RepairElectrical/Electronic SystemsEasy
A technician is checking the charging system. With the engine running, a voltmeter shows 14.5 volts across the battery terminals. When the headlights, blower motor, and rear defroster are turned on, the voltage drops to 13.8 volts. What does this indicate?
- AThe alternator is failing due to excessive load.
- BThe charging system is overcharging the battery.
- CThe charging system is functioning normally.
- DThe battery has an internal short.
Show answer & explanationAnswer & explanation
Correct answer: C. The charging system is functioning normally.
A healthy charging system typically maintains voltage between 13.5 and 14.8 volts. A drop from 14.5V to 13.8V when additional loads are applied is normal, as the alternator adjusts its output to meet the demand while still maintaining voltage within the acceptable range.
Why the other options are wrong
- A. The alternator is successfully maintaining voltage within the normal range under load, indicating it is functioning correctly and meeting the electrical demands, not failing.
- B. Overcharging would be indicated by voltages consistently above 15 volts, not 13.8-14.5V.
- D. An internal short in the battery would likely cause low voltage even with the engine running, or prevent the battery from holding a charge, not a normal voltage drop under load.
Normal Charging System Voltage
A healthy charging system maintains system voltage within a specified range, typically 13.5V to 14.8V, under various electrical loads.
- Voltage should be checked with the engine running and at a fast idle.
- A slight voltage drop is normal when heavy electrical loads are applied.
- Consistent voltage below 13.0V or above 15.0V indicates a problem.
Memory trick: Voltage in the zone, system's well known.