A technician is diagnosing a complaint that the vehicle's right front turn signal illuminates but does not flash, and the corresponding dashboard indicator also illuminates steadily. All other turn signals and the hazard lights operate correctly. What is the MOST likely cause?
- AA defective flasher relay.
- BA short to ground in the right front turn signal circuit.
- CAn open circuit in the right rear turn signal bulb filament.
- DA faulty turn signal switch.
Show answer & explanationAnswer & explanation
Correct answer: C. An open circuit in the right rear turn signal bulb filament.
Modern electronic flasher relays often detect current draw. If one bulb in a circuit is open, the total current draw for that side decreases, causing the flasher to illuminate steadily rather than flash, or to flash rapidly (hyper-flash) if the remaining bulb has too little resistance. Since only one side is affected and the hazard lights work, the flasher relay is likely fine. A steadily lit indicator and non-flashing bulb on one side often points to an open circuit (e.g., a blown bulb) in the other bulb on the same circuit.
Why the other options are wrong
- A. A defective flasher relay would either affect all turn signals and hazards, or prevent any flashing altogether. Since other signals and hazards work, the flasher is likely not the primary issue.
- B. A short to ground in the right front turn signal circuit would likely blow a fuse, causing no illumination at all for that circuit.
- D. A faulty turn signal switch would typically affect either both front and rear signals on one side, or all turn signals if it's the common contact, and would likely prevent illumination entirely or cause incorrect operation for both bulbs.
Electronic Flasher Relay Logic
Electronic flasher relays monitor current draw to detect bulb failures. A reduced current (due to an open circuit like a blown bulb) can cause the remaining bulbs on that side to illuminate steadily or hyper-flash, and the dash indicator to behave similarly.
- Flasher relays detect current changes.
- Open circuit (blown bulb) reduces current.
- Steady illumination or hyper-flash indicates a bulb issue.
- Affects only the side with the fault, not both.
Memory trick: If the light is stuck 'on' and not blinking, it's probably missing its buddy bulb.