2021 Mercedes-Benz AMG GT Headlamp Fogging TSB

Symptoms of Headlamp Fogging or Leaks

Owners of the 2021 Mercedes-Benz AMG GT may observe the following issues related to their vehicle's lighting system:

• Headlamps leaking or fogged: Visible condensation or moisture inside the headlamp assembly.
• "Lighting > Exterior lights > Front fog lights > Malfunction"
• "Lighting > Exterior lights > Driving lights > Main headlamps > Fogged"
• "Lighting > Exterior lights > Driving lights > Taillamp > Fogged"

It's important to distinguish between natural physical fogging, which does not impair headlamp function, and actual leaks. This TSB outlines procedures to make that distinction for any Mercedes-Benz AMG GT headlamp fogging concerns.

Diagnosis and Trigger Conditions

Diagnosing the cause of headlamp fogging on your Mercedes-Benz AMG GT involves two main approaches: checking for external damage and performing an overpressure leak test.

Checking for External Damage

Technicians will first inspect the headlamps for any visible external damage:

• For headlamps with a closed system: They will check the headlamps for external damage and ensure the Gore-diaphragm and cover caps are correctly seated and latched. If external damage is found, the headlamp should be replaced.
• For headlamps with an open system: The vent must be sealed, and cover caps latched correctly. If external damage is present, the headlamp requires replacement.

Overpressure Leak Test

If no external damage is apparent, an overpressure leak test is performed to definitively determine if the headlamp is leaky or if the fogging is natural. This test involves:

1. Connecting a specialized test adapter (part number W000589059100) to a pressure tester.
2. Checking the test adapter itself for leak tightness by applying a maximum overpressure of 30 mbar. The pressure must remain constant, indicating a sealed system.
3. Sealing all headlamp vents with sealing compound and the existing diaphragm with a stamp.
4. If necessary, the headlamp may need to be removed to access the diagnostic socket on its housing.
5. Plugging the adapter onto the headlamp's diagnostic socket.
6. Applying a maximum of 30 mbar overpressure to the headlamp housing.
7. Observing the pressure drop over 30 seconds. A pressure drop of less than 10 mbar indicates the headlamp is tight, and any fogging is natural physical condensation. A pressure drop greater than 10 mbar within 30 seconds signifies a leaky headlamp. Soap suds can be used to pinpoint the exact leak location.

Repair Procedure Summary

The repair procedure depends on the diagnosis.

Clearing Fogged or Condensed Headlamps

If the headlamps are fogged due to natural condensation, the following steps are performed to clear them:

1. The vehicle is driven into a workshop where the temperature is higher than +18 °C (+64.4°F).
2. The engine is switched off, and battery support is connected via a charger.
3. The hood or trunk is opened.
4. The lights are switched on.
5. The vehicle is left in this state for 60 minutes.
6. Technicians will check for a significant reduction in condensation. If the condensation has disappeared, no further action is needed.

Addressing Leaky Headlamps

If the overpressure test confirms the headlamp is leaky and the cause cannot be rectified, the headlamp must be replaced. Mercedes-Benz reference manual AR82.10-P-5455WT provides further guidance for the pressure test and is used for all closed headlamps. For open headlamp systems, vent ducts must be sealed before testing.

Required Tools or Parts

To perform the overpressure leak test, a specific tool is required:

• Test adapter: Part number W000589059100.

Important Warnings

Owners and technicians should be aware of the following:

• External damage to the headlamp does not qualify for warranty or goodwill coverage.
• During the overpressure leak test, exceeding a maximum overpressure of 50 mbar can damage the headlamp seal.
• If a headlamp is replaced, no dry packs should be installed on the new replacement headlamp.

What Owners Should Do

If you experience headlamp fogging or suspect a leak on your 2021 Mercedes-Benz AMG GT, it is recommended to visit an authorized Mercedes-Benz service center. They have the specialized tools and training to accurately diagnose whether the fogging is natural condensation or a true leak requiring repair, following the procedures outlined in TSB LI82.10-P-078896. This will address any Mercedes-Benz AMG GT headlamp fogging concerns effectively.

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Source: NHTSA ID 11017500