Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A client complains that the vehicle's turn signals flash rapidly on one side, but the bulbs appear to be working correctly. A technician uses a scan tool to check for body control module (BCM) fault codes but finds none. Which of the following is the MOST likely cause of this condition?
- AA parasitic drain on the BCM.
- BAn incorrect wattage bulb installed in one of the turn signal lamps.
- CA faulty turn signal switch.
- DA short to voltage in the turn signal circuit.
Show answer & explanationAnswer & explanation
Correct answer: B. An incorrect wattage bulb installed in one of the turn signal lamps.
Rapid flashing of turn signals is a common indicator of a lower-than-expected current draw, often caused by a burned-out bulb or, in this case, an incorrect wattage bulb. Modern vehicles monitor current and flash rapidly to alert the driver of a potential issue. If all bulbs appear to be working, an incorrect wattage bulb is a strong suspect.
Why the other options are wrong
- A. A parasitic drain affects battery life and overall electrical system, not specifically turn signal flash rate.
- C. A faulty turn signal switch might cause no operation or constant operation, but not typically rapid flashing with all bulbs working.
- D. A short to voltage would likely cause a blown fuse or constant illumination, not rapid flashing.
Hyperflashing (Turn Signals)
Rapid flashing of turn signals, typically indicating a circuit fault, most commonly a burned-out bulb, or sometimes an incorrect wattage bulb.
- Modern vehicles monitor current draw in turn signal circuits.
- Lower-than-expected current draw triggers hyperflashing.
- Can be caused by a failed bulb, incorrect bulb, or corroded socket.
Memory trick: Fast Flashes Signal Low Current's Sneaky Presence.