The brake lights on a 2012 Hyundai Sonata use a single type of bulb: a 12-volt dual-filament bulb, commonly referred to as a 3157, for each rear taillight assembly.
In other words, each rear brake/taillight unit uses one 3157 bulb. The two filaments in the bulb power the tail and brake functions, giving you tail illumination when headlights are on and bright brake lighting when you press the pedal. Always verify the exact bulb type for your specific car by checking the bulb in the housing or the owner's manual if needed.
Bulb specification and compatibility
The standard choice for the 2012 Sonata is a 12-volt dual-filament bulb with the designation 3157. Because it is a dual-filament design, the bulb has two independent filaments: one for the dim tail light and one for the brighter brake light. Left and right rear taillights each use one 3157 bulb. If you order bulbs from an aftermarket source, you may encounter variants in naming like 3157NA or other regional designations, but they are generally cross-compatible so long as the base and voltage match the factory socket.
What dual-filament means for brake and tail functions
With a dual-filament bulb, the same lamp provides both functions. The brighter filament activates with the brake switch, while the dimmer filament is used for normal tail lighting when the headlights are on. Replacing the bulb with a standard 3157 dual-filament unit will restore both functions in the same housing.
How to replace the brake light bulb
Replacement is a routine maintenance task you can perform with basic tools. The following steps describe a typical process for the Sonata, but if you have a different trim or market, consult the manual or inspect the socket to confirm specifics.
- Open the trunk and remove any interior cover or access panel to reach the taillight assembly.
- Disconnect the electrical connector from the taillight socket.
- Twist the bulb socket counterclockwise to release it from the housing.
- Pull the old 3157 bulb straight out of the socket.
- Insert the new 3157 dual-filament bulb into the socket and twist to lock it back into the housing.
- Reconnect the electrical connector, reattach the interior cover, and test the brake and tail lights by pressing the brake pedal and turning on the running lights.
Note: If one side has burned-out bulbs, it is common to replace both taillight bulbs on that side to ensure balanced brightness and color. Always test both sides after replacement.
Tips and notes
For best results, purchase a reliable brand and ensure you select a 12-volt 3157 dual-filament bulb (not a single-filament type). Some regional markets may use different turn-signal bulbs in the same housing, so if your turn signal behavior seems off or you see differences in color, check the turn-signal bulb specification as well.
Summary
In a 2012 Hyundai Sonata, the brake lights use 3157 dual-filament bulbs, one per rear taillight. Replacing them is straightforward: remove the interior trunk panel, swap in a new 3157, and test. Always verify compatibility for your specific vehicle variant and replace in pairs if needed to maintain even brightness and color balance.