A technician is diagnosing an intermittent issue where the vehicle's turn signals sometimes flash rapidly on one side, while the bulbs on that side appear to be working correctly. All bulbs illuminate, but the flash rate is much faster than normal. What is the MOST likely cause of this 'hyperflashing' without a visibly failed bulb?
- AA faulty flasher relay or control module.
- BA short to ground in the turn signal circuit.
- CIncreased resistance in the ground circuit of one or more bulbs.
- DThe installation of incorrect wattage (lower resistance) LED bulbs.
Show answer & explanationAnswer & explanation
Correct answer: D. The installation of incorrect wattage (lower resistance) LED bulbs.
Hyperflashing (rapid flashing) is a safety feature designed to alert the driver to a burnt-out bulb. The flasher unit (or control module) monitors the current draw of the circuit. If the total current draw is significantly lower than expected (as with lower resistance LED bulbs that draw much less current than incandescent bulbs), the system interprets this as a 'burnt-out' bulb and initiates hyperflashing, even if the new bulbs are working. The bulbs are working, but the system's resistance/current sensing is fooled.
Why the other options are wrong
- A. While a faulty flasher relay can cause incorrect flash rates, hyperflashing is specifically a low-current detection. If all bulbs are working, a faulty flasher is less likely than a change in load.
- B. A short to ground would likely cause a blown fuse or a constant illumination, not hyperflashing with all bulbs working.
- C. Increased resistance in a ground circuit would *reduce* current flow, which could contribute to hyperflashing. However, the scenario states all bulbs are working, and the most common cause of hyperflashing with working bulbs is a *reduction* in total circuit resistance from LED bulbs, which draw less current.
Hyperflashing (LED Bulbs)
Hyperflashing of turn signals, even with all bulbs visually working, often occurs when lower-current LED bulbs replace incandescent bulbs. The flasher unit detects the reduced current draw as a 'burnt-out' bulb and triggers the rapid flash rate.
- Flasher unit monitors circuit current draw.
- LEDs draw much less current than incandescent.
- Requires load resistors or a compatible LED flasher relay to correct.
Memory trick: Fast flash, all lights bright, LED change, not quite right.