The quick answer: most 2018 Sierra models use H11 bulbs for the low beams, 9005 bulbs for the high beams, and H11 for the fog lights. Some higher-trim variants with factory HID or LED headlights use different bulb configurations, so verify your specific build.
Details follow to explain the typical configurations and how to confirm the exact bulb for your truck.
Headlight bulb types by function
Here is a concise rundown of the bulb types you’re likely to encounter for the Sierra’s headlight functions on typical configurations.
- Low beam: H11 (most halogen projector systems in 2014–2018 Sierra 1500s)
- High beam: 9005 (HB5)
- Fog lights: H11
These are the most common halogen configurations. If your Sierra uses HID or LED headlights, the bulbs and replacement approach will differ.
Trim and headlight options
GM offered different headlight setups for the 2018 Sierra depending on trim and option packages. The following outlines the typical scenarios and what to look for when shopping for bulbs.
- Halogen headlights (base and many mid trims): low beam H11, high beam 9005, fog H11
- HID headlights (available on some higher trims): low beam typically a D1S or D2S-type bulb depending on the exact assembly; the high beam and fog light configuration can vary
- LED headlights (rare on 2018 Sierra; when present, headlight modules are usually not user-replaceable bulbs)
Bottom line: If your Sierra uses halogens, the listed H11/9005 bulbs apply. If you have HID or LED headlights, refer to the owner’s manual or dealer for the exact replacement bulbs or module information.
Summary
In most cases, a 2018 GMC Sierra with halogen headlights uses H11 for low beams, 9005 for high beams, and H11 for fog lights. Higher trims with HID or LED headlights use different bulb types or integrated modules. Always verify the exact configuration via the owner’s manual, the headlight housing label, or a dealer lookup by VIN.