Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsLighting Systems Diagnosis and RepairHard
A technician is diagnosing a complaint where the vehicle's headlights occasionally flicker or dim, especially when other electrical accessories (e.g., power windows, defroster) are activated. This issue occurs with the engine running. What is the most probable cause?
- AAn intermittent open circuit in the headlight wiring
- BA parasitic draw on the battery
- CA failing alternator or charging system
- DA faulty headlight switch
Show answer & explanationAnswer & explanation
Correct answer: C. A failing alternator or charging system
Flickering or dimming lights when other electrical loads are activated, specifically with the engine running, strongly suggests the charging system (alternator) is struggling to provide sufficient current to meet the vehicle's electrical demands, leading to voltage drops across the system.
Why the other options are wrong
- A. An intermittent open in the headlight wiring would cause the headlights to go out or flicker independently, but not necessarily in correlation with other accessory activation.
- B. A parasitic draw affects the battery when the vehicle is off, leading to a dead battery, not flickering lights while running.
- D. A faulty headlight switch would typically cause intermittent or complete failure of the headlights, not a general system-wide dimming when other loads are activated.
Charging System Insufficiency
When the alternator cannot supply enough current to meet the vehicle's electrical demands, leading to voltage drops and flickering lights.
- Occurs with engine running and electrical loads on.
- Indicates a weak alternator, loose belt, or poor connections.
- Can be diagnosed by measuring charging voltage under load.
Memory trick: Load's a pain, alternator's stain!