Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsLighting Systems Diagnosis and RepairEasy
A client complains that their vehicle's dashboard turn signal indicator lights illuminate but do not flash, and the exterior turn signals also do not flash. All other lights on the vehicle are operating correctly. Which of the following is the MOST likely cause?
- AA defective flasher relay
- BA faulty turn signal switch
- CA short circuit in the turn signal wiring
- DAn open circuit in one of the turn signal bulbs
Show answer & explanationAnswer & explanation
Correct answer: A. A defective flasher relay
If the turn signal indicator lights illuminate but do not flash, and the exterior turn signals also do not flash, it points to a failure in the component responsible for the flashing action—the flasher relay. Other issues would typically prevent illumination or cause hyper-flashing.
Why the other options are wrong
- B. A faulty turn signal switch would likely prevent the lights from illuminating or cause them to stay on without flashing only on one side, not both.
- C. A short circuit in the turn signal wiring would likely blow a fuse or prevent the lights from illuminating at all, rather than causing them to illuminate steadily without flashing.
- D. An open circuit in a turn signal bulb would typically cause hyper-flashing on the affected side, not a complete lack of flashing on both sides.
Flasher Relay Function
The flasher relay is an electrical component in a vehicle's turn signal and hazard light circuits responsible for intermittently interrupting the current to cause the lights to flash.
- Creates the on-off blinking action for turn signals and hazard lights.
- Can be thermal, electromechanical, or electronic.
- Failure often results in no flashing (lights stay on or off) or incorrect flash rate.
Memory trick: No Flash? Check the Flasher!