The Saturn Sky front turn signal uses a 4157NA bulb size while the rear turn signal requires a 3157 bulb size. The replacement chart covers 2007 to 2010 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Saturn Sky uses the 4157NA bulb for the front turn signal across all model years from 2007-2010.
The 4157NA is a dual-filament wedge bulb classified under the T25 envelope, rated at 12V with a 27W high filament and a 7W low filament, conforming to ANSI standards recognized in both the US and Canada.
The "NA" suffix in the 4157NA designation indicates natural amber glass, meaning the bulb produces an amber-colored output without relying on a colored lens to achieve the required turn signal hue.
The Saturn Sky uses the 3157 bulb for the rear turn signal across all model years from 2007-2010.
The 3157 shares the same T25 wedge form factor, dual-filament design, 12V operating voltage, and 27W/7W power rating as the 4157NA, but its glass envelope is clear rather than naturally amber-tinted.
Because the 4157NA and 3157 share the same T25 wedge base and electrical ratings, they are physically interchangeable in terms of socket fitment, though substituting a clear 3157 in a front position that relies on the bulb's own amber glass for color compliance would affect the amber output of the turn signal.
The dual-filament construction in both bulb types allows a single bulb to serve two lighting functions, with the higher 27W filament typically assigned to the turn signal or brake function and the lower 7W filament assigned to a running or parking light function.