2018 GMC Sierra 1500 Bulb Size Chart and Replacement Guide

As an ASE-certified master technician, I’ve seen my fair share of lighting issues on the 2014-2018 GM truck platform. The 2018 GMC Sierra 1500 is a fantastic truck, but its lighting system can be slightly confusing due to the massive variation between trim levels. Depending on whether you have a base model, SLE, SLT, or Denali, you might be dealing with High-Intensity Discharge (HID) bulbs, standard incandescent bulbs, or full sealed LED assemblies.

Below is your comprehensive guide to the 2018 GMC Sierra 1500 bulb sizes, upgrades, and replacement tips.

Quick reference: 2018 GMC Sierra 1500 Bulb Sizes

Note: Trim levels heavily dictate your bulb types. SLT and Denali trims feature integrated LED headlights and taillights which cannot be replaced with a simple bulb; the entire assembly must be replaced if they fail. Base and SLE models typically feature HID headlights and incandescent tail bulbs.

LED vs Halogen Upgrade Considerations

Upgrading your incandescent turn signals, reverse lights, or interior lights to LED is a popular modification for the 2018 Sierra, but it requires some planning.

CANBUS Errors and Hyperflashing: The Sierra’s Body Control Module (BCM) monitors the electrical draw of the vehicle's exterior lights. Because LEDs draw significantly less power than halogen/incandescent bulbs, the BCM might think the bulb is burned out. This results in "hyperflashing" (rapid blinking) of your turn signals or error messages on the dash. To fix this, you will need LED bulbs with built-in CANBUS decoders, or you will need to wire in an inline load resistor for each turn signal bulb you replace.

Headlight Upgrades: If your truck has the 25-watt D5S HID headlights, you might find them lacking compared to modern LED setups. Upgrading from D5S to LED requires specific D5S-to-LED conversion bulbs that can interface with the factory HID ballast, or bypassing the ballast entirely.

How to Replace Each Bulb

Here are a few quick technician tips for tackling these replacements:

• Headlights (D5S): Replacing the D5S HID bulbs on the Sierra requires patience. The easiest way to access the rear of the headlight housing is by removing the airbox on the passenger side and moving the battery or washer fluid neck on the driver’s side. You have to remove the dust cover, twist the D5S bulb counter-clockwise, and disconnect the integrated igniter plug.
• Fog Lights (PSX24W): Access these from underneath the front bumper. Turn the wheel inward to give yourself room, reach up behind the bumper corner, squeeze the release tabs on the wiring harness, and twist the bulb out.
• Front Turn Signals (7443): These can usually be accessed from the top engine bay or by pulling back the front wheel well liner (fender liner). Twist the socket counter-clockwise to remove.
• Tail, Brake, and Reverse Lights (7443 / 921): Open the tailgate and remove the two T15 Torx screws holding the taillight assembly in place. Pull the assembly straight back toward you (do not pull sideways, or you will snap the plastic alignment pins). Twist the sockets to replace the bulbs. (Note: If you have the SLT/Denali LED taillights, there are no replaceable bulbs inside; you must replace the whole housing).
• License Plate (194): Reach under the rear bumper, twist the socket counter-clockwise, and pull the 194 bulb straight out.
• Interior Dome/Map (194/211-2): Use a plastic non-marring trim tool to carefully pry the clear plastic lenses off. Do not use a metal flathead screwdriver, or you will crack the lens.

Common Lighting Issues for this Generation

Moisture in Taillights: A very common issue on the 2014-2018 Sierra is condensation building up inside the taillight housings, especially on the premium LED versions. This can short out the LED boards.

HID Ballast/Igniter Failure: If a D5S headlight goes out, don't immediately assume it's just the bulb. Because the D5S bulb has an integrated igniter, replacing the bulb usually fixes the issue. However, if the issue persists, the main ballast mounted to the bottom of the headlight housing may have suffered water damage or failed.

DRL Strip Yellowing or Burning Out: The C-shaped LED Daytime Running Light strips on these headlights look fantastic, but over time, the LED drivers can overheat and burn out segments of the strip. Unfortunately, this usually requires a complete headlight assembly replacement.

If you are dealing with complex electrical issues, BCM codes, or you simply don't want to wrestle with removing your grille to replace a headlight assembly, it's always best to let a professional handle it.

Find a trusted shop on Repairius.