2021 Mercedes-Benz AMG GT Headlamp Fogging TSB

Mercedes-Benz has released Technical Service Bulletin (TSB) LI82.10-P-078301, version 4, dated March 9, 2026, to address concerns regarding headlamp and front fog lamp fogging or leaking. This TSB applies to all Mercedes-Benz cars except G-Class models before model year 2018, with model series added to the validity.

Symptoms

Owners of affected vehicles, including the 2021 Mercedes-Benz AMG GT, may observe the following issues:

• "Lighting > Exterior lights > Front fog lights > Malfunction"
• "Lighting > Exterior lights > Driving lights > Main headlamps > Fogged"
• "Lighting > Exterior lights > Driving lights > Taillamp > Fogged"

These symptoms are generally described as "Headlamp, front fog lamp leaky or fogged" in the complaint section of the TSB.

Cause of Headlamp Fogging

Mercedes-Benz states that fogging of the headlamps is a natural phenomenon. This can occur under specific climatic conditions and does not typically indicate a technical impairment of the headlamp itself. Many lamp units are designed as a "closed system" if a pressure compensation diaphragm is fitted in the housing cover, which helps manage internal pressure changes.

Important Warnings for Owners

Owners should be aware of several key points regarding the Mercedes-Benz AMG GT headlamp fogging issue:

• Natural Phenomenon: "It is not physically possible to defog the headlamps completely. Fogging does not impair the operation or the service life of the headlamp."
• Warranty Coverage: "External damage to the headlamp/rear lamp or faulty seating of the cover caps does not present a warranty or goodwill case." This means that if the fogging is due to physical damage or improper installation of covers, it may not be covered.

Diagnosis and Repair Procedure Summary

This TSB outlines two main remedies for addressing headlamp fogging.

Remedy 1: Clearing Fogged/Condensed Headlamps

This procedure is designed to clear condensation from LED, halogen/xenon headlamps, and LED rear lamps on electric vehicles. It involves specific workshop conditions and steps:

1. The vehicle must be driven into a workshop where the temperature is higher than 64.4 °F (18 °C). Exhaust extraction equipment should be connected.
2. The engine must be switched off, and battery support connected via a charger.
3. The hood should be opened (or the front-end flap for electric vehicles, ensuring sufficient ventilation).
4. The vehicle's lights must be switched on.
5. The vehicle should remain in this state for 60 minutes.
6. After 60 minutes, technicians must check for a significant reduction in condensation, indicating successful thawing.

Note: Technicians are advised not to perform an engine wash before the defogging test. Remedy 1 is specifically recommended for model series 463 (from model year 2018) and model series 465, which include certain G-Class models.

Remedy 2: Identifying a Defective Headlamp

If Remedy 1 does not significantly reduce condensation, or if a defect is suspected, technicians should perform further checks:

1. Inspect the headlamp for external damage and verify that the cover caps and pressure compensation diaphragm are correctly seated.
2. Check the electrical connectors, including plugs and pins, for proper connection.
3. Perform a leak tightness test according to TSB LI82.10-P-078307. This test is exclusively for headlamps.
4. If external damage is found on the headlamp or rear lamp, the component should be replaced following the Workshop Information System (WIS) instructions.

For recurring Mercedes-Benz AMG GT headlamp fogging problems, it is possible to install desiccant packs. This may involve addressing the open ventilation system (LI82.10-P-078302) or the closed ventilation system (LI82.10-P-078304).

Owner Action

If you are experiencing headlamp or fog lamp fogging on your 2021 Mercedes-Benz AMG GT, it is recommended to visit an authorized Mercedes-Benz service center. Technicians can perform the diagnostic and repair procedures outlined in TSB LI82.10-P-078301 to determine the cause and appropriate solution for the Mercedes-Benz AMG GT headlamp fogging.

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NHTSA ID: 11029959