DIAGNOSE – THE TURN SIGNALS FLASH TOO SLOW

By Carl O’Reilly

SYMPTOM SUMMARY
The turn signals flash too slow in one or both directions.

USUAL CAUSE
The usual cause of this symptom is a burnt out or incorrect bulb on the side that is malfunctioning. The turn signals use a flasher unit that acts as a repetitive circuit breaker. This unit makes then breaks the electrical circuit that turns on the turn signal bulbs. The cycle will continue as long as the directional switch is turned on. This unit relies on heat build up caused by electrical current flow to determine when to break the circuit. When the switch is initially turned on, electrical current flows through the flasher unit to the bulbs. When this occurs heat builds up in the flasher unit. When the heat reaches a predetermined temperature, a metal strip within the unit stretches due to the heat and breaks the electrical circuit turning the bulbs off. With the bulbs disconnected from the circuit, the flasher unit cools off. Once it has cooled, the metal strip re-contracts and re-closes the electrical circuit turning the bulbs back on. If one of the bulbs in the circuit is defective the flasher will take longer to heat up and break the electrical circuit. This can cause an abnormally slow flash rate.

DIAGNOSIS
Turn on the directionals on the side that is malfunctioning. Inspect each bulb to ensure it is functional.

PRECAUTIONS, TIPS, and NOTES
You should always use a replacement bulb of the same part number as the one being replaced. Your owner’s manual will indicate the correct bulbs for each location on the vehicle. Using the incorrect bulb can create too slow or rapid turn signal operation. Manufacturers often use grease to repel water from the bulb sockets. Do not remove this grease from the bulb socket when replacing defective bulbs.