Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGauges, Warning Devices, and Driver Information Systems Diagnosis and RepairHard
A customer reports that the vehicle's turn signals flash rapidly on one side, but the bulbs appear to be functioning correctly both inside and outside the vehicle. What is the most likely cause?
- AA faulty turn signal flasher relay.
- BA faulty turn signal switch.
- CA wiring short to power in the turn signal circuit.
- DA bulb with incorrect wattage installed.
Show answer & explanationAnswer & explanation
Correct answer: D. A bulb with incorrect wattage installed.
The rapid flashing (hyper-flashing) of turn signals is a diagnostic feature designed to alert the driver to a burnt-out bulb. If all bulbs appear functional, but the hyper-flashing still occurs, it often indicates that one of the bulbs, while illuminating, has an incorrect (lower) wattage, causing the flasher unit to 'think' there's less load than expected, thus triggering the rapid flash.
Why the other options are wrong
- A. A faulty flasher relay would typically cause all signals to flash incorrectly, or not at all, not just one side and with all bulbs appearing functional.
- B. A faulty turn signal switch would typically cause no operation, intermittent operation, or constant operation, not rapid flashing with all bulbs appearing functional.
- C. A wiring short to power would likely cause the lights to be constantly on or blow a fuse, not rapid flashing.
Turn Signal Hyper-Flashing
Turn signal hyper-flashing (rapid flashing) is a system diagnostic indicating a burnt-out bulb or, if all bulbs are visibly working, an incorrect wattage bulb causing a low current draw.
- Flasher unit monitors current draw.
- Low current draw mimics a burnt bulb.
- Incorrect wattage bulb draws less current.
Memory trick: Rapid flash, all bulbs glow: 'WRONG WATTAGE', the flasher 'DON'T KNOW'.