Replace or repair the center high-mounted stop lamp (CHMSL/third brake light) assembly on the rear cab of a 2014-2018 Chevrolet Silverado 1500.

Warnings

Tools required

Parts

• CHMSL assembly (center high-mounted stop lamp) × 1 — GM 84213308 or equivalent LED assembly
• Foam seal gasket (if damaged) × 1 — Typically included with CHMSL assembly

Preparation

1. Park vehicle on level surface, engage parking brake, and place transmission in Park
2. Turn ignition off and remove key
3. Chock front wheels if working from truck bed
4. Allow vehicle to cool if recently driven (exterior panels may be hot)
5. Clean area around third brake light assembly to prevent debris from entering cab or electrical connections
6. If testing electrical function, have an assistant available or use a brake pedal depressor

Procedure

1. 1

   Access the CHMSL assembly
   Open the rear window if equipped with a sliding rear window to provide interior access if needed. Position step stool or ladder to safely access the rear cab panel above the bed. The CHMSL assembly is centered on the rear cab panel just above the rear window.
2. 2

   Remove CHMSL mounting fasteners
   Locate the two T20 Torx screws on the exterior of the CHMSL lens assembly. These are typically located on the top or sides of the light housing. Using the T20 Torx driver, remove both screws completely. Keep screws in a safe location as they may have captive washers or seals.
3. 3

   Separate CHMSL assembly from cab
   Gently pull the CHMSL assembly away from the cab panel. There is a foam gasket seal that may create resistance. If the assembly is stuck, use a plastic trim tool to carefully release it. Do not pull on the wiring harness. The assembly should come out 2-3 inches while still connected to the wiring.
4. 4

   Disconnect electrical connector
   Locate the electrical connector at the back of the CHMSL assembly. Press the release tab on the connector (typically on top or side) while pulling the connector straight away from the lamp assembly. Do not pull on wires. If connector is difficult to access, you may need to reach through the rear window or access point inside the cab to release it from the interior side.
5. 5

   Inspect and test (if diagnosing)
   If diagnosing a lighting issue, inspect the bulb socket or LED board for corrosion, water damage, or burnt contacts. Check the foam gasket seal for deterioration. Using a multimeter, verify power and ground at the vehicle-side connector with brake pedal depressed (should show 12V). If testing the removed lamp, apply 12V power to verify LED or bulb function.
6. 6

   Prepare new or repaired assembly
   If installing a new CHMSL assembly, verify the foam gasket seal is properly positioned on the back of the new lamp housing. If reusing the original assembly after bulb replacement or repair, clean the mounting surface on the lamp and ensure the gasket is intact and properly seated. Replace gasket if torn, compressed, or deteriorated.
7. 7

   Connect electrical connector
   Align the electrical connector and push firmly until you hear or feel a positive click. Gently tug on the connector to verify it is fully seated and locked. Do not force misaligned pins.
8. 8

   Position and secure CHMSL assembly
   Carefully align the CHMSL assembly with the mounting holes in the cab panel. Ensure the foam gasket is properly positioned to create a weatherproof seal. Press the assembly firmly against the cab panel. Install both T20 Torx screws and tighten by hand initially to ensure proper alignment. Tighten screws evenly in a cross-pattern to compress the gasket seal uniformly. Final torque should be snug but do not overtighten as this can crack the lens housing—approximately 2-3 Nm (18-27 lb-in) hand-tight is sufficient for plastic lamp housings.

Reassembly

1. Ensure CHMSL assembly is flush against cab panel with no gaps that could allow water intrusion
2. Verify both mounting screws are secure and evenly tightened
3. Close rear sliding window if it was opened during installation

Verification

• Turn ignition to ON position (engine does not need to be running)
• Have an assistant press and hold the brake pedal while you verify the third brake light illuminates fully and brightly
• Check that all LED segments illuminate (if LED type) or bulb is bright with no flickering
• Verify no warning lights appear on instrument cluster related to brake lamp circuit
• Inspect the seal around the CHMSL assembly for proper contact with no visible gaps
• Test brake lights at least twice more (press and release brake pedal) to confirm consistent operation
• Road test vehicle in safe area and verify brake lights function during actual braking if possible

More procedures for this vehicle