Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsLighting Systems Diagnosis and RepairHard
A vehicle's dashboard turn signal indicator lights illuminate but do not flash, and the exterior turn signals do not illuminate at all. The hazard lights also fail to operate. What is the most likely cause?
- AAn open circuit in the ground wire for the turn signal bulbs
- BA faulty multi-function switch
- CA blown fuse for the turn signal circuit
- DA faulty turn signal flasher relay
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty turn signal flasher relay
If the dashboard indicators illuminate (meaning the multi-function switch is sending a signal) but don't flash, and the exterior lights don't come on at all (even with hazards), it points to a failure of the flasher relay. The flasher is responsible for interrupting the circuit to create the flash and often powers both the exterior lights and the flashing action of the indicators.
Why the other options are wrong
- A. An open ground for the bulbs would prevent the exterior lights from working, but the dash indicators would still flash (or try to) and the flasher would operate, potentially at a rapid rate.
- B. A faulty multi-function switch might prevent a signal from reaching the flasher, but the dash indicators wouldn't illuminate at all if the switch was completely dead.
- C. A blown fuse would typically prevent the dash indicators from lighting up as well, or prevent power from reaching the flasher entirely.
Flasher Relay Failure Modes
Common symptoms of a failing turn signal flasher relay include no flash, solid-on lights, or no light output at all.
- Controls both turn signals and hazard lights.
- Can be thermal or electronic.
- Failure affects all lights connected to it.
Memory trick: No flash, no light, flasher's plight!