ASE G1 Auto Maintenance and Light RepairElectrical/Electronic SystemsMedium
A vehicle's headlights are dim, and the engine cranks slowly but eventually starts. After starting, the charging system indicator light remains illuminated. A voltmeter connected across the battery terminals while the engine is running reads 12.2 volts. What is the MOST likely problem?
- AA faulty battery.
- BExcessive parasitic draw.
- CA seized alternator pulley.
- DA slipping or broken alternator drive belt.
Show answer & explanationAnswer & explanation
Correct answer: D. A slipping or broken alternator drive belt.
Dim headlights, slow cranking, and a charging system light remaining on all point to an undercharged battery. A running voltage of 12.2V indicates the alternator is not charging the battery. A slipping or broken alternator belt would prevent the alternator from spinning and generating voltage, leading to these symptoms.
Why the other options are wrong
- A. While the battery is discharged, the core problem is why it's not being recharged, as indicated by the charging light and low running voltage.
- B. Excessive parasitic draw would discharge the battery when the vehicle is off, but once the engine is running, a healthy charging system should still maintain proper voltage and turn off the charging light.
- C. A seized alternator pulley would likely cause a squealing belt and potentially a broken belt, but the primary issue described is lack of charging, not the pulley itself.
Charging System Failure Symptoms
Symptoms of a failing charging system include an illuminated charging indicator light, low system voltage, and a discharged battery.
- Normal charging voltage is typically 13.5-14.8 volts with the engine running.
- A voltage reading near battery voltage (e.g., 12.2V) with the engine running indicates no charging.
- Common causes include alternator failure, drive belt issues, or wiring problems.
Memory trick: Light on, volts low, belt's gone, no charge flow.