2021 Mercedes-Benz AMG GT Rear Lamps Fogged Up TSB

Symptoms

Owners of the 2021 Mercedes-Benz AMG GT may observe that their vehicle's rear lamps are fogged up or appear not to be leaktight. This condition is categorized under "Lighting > Exterior lights > Driving lights > Taillamp > Fogged" in service documentation.

Diagnosis and Trigger Conditions

Fogging of the rear lamps is frequently a natural phenomenon, especially under certain climatic conditions. Mercedes-Benz states that this does not necessarily indicate a technical impairment of the rear lamps or their functionality. Simultaneous fogging of multiple lamp components also suggests extreme environmental conditions rather than a defect.

However, if the fogging persists or is severe, it could indicate a defective lamp. Technicians are instructed to differentiate between natural condensation and actual defects.

Repair Procedure Summary

Mercedes-Benz TSB LI82.10-P-078069 outlines two main remedies for addressing fogged rear lamps on the 2021 Mercedes-Benz AMG GT.

Remedy 1: Clearing Fogged/Condensed Rear Lamps

This procedure aims to clear condensation from the rear lamps without replacement:

1. Vehicle Preparation: Drive the vehicle into a workshop where the ambient temperature is higher than +18 °C (64.4 °F).
2. Power Management: Switch off the engine and connect battery support via a charger.
3. Access: Open the trunk.
4. Activation: Switch on the exterior lighting.
5. Defogging Period: Leave the vehicle in this state for 60 minutes.
6. Inspection: After 60 minutes, check for a significant reduction in condensation, indicating successful defogging progress.

If, after this procedure, no reduction in the degree of fogging is visible, the rear lamp is considered defective and must be replaced.

Remedy 2: Identifying a Defective Rear Lamp

If the fogging persists or if there are other signs of a defect, technicians should perform the following checks to identify a truly defective rear lamp:

1. External Damage Check: Inspect the rear lamps for any external damage, and ensure that the differential aeration cells and the diaphragm are correctly seated. If external damage is found, the component parts must be replaced according to Mercedes-Benz Workshop Information System (WIS) instructions.
2. Electrical Connector Check: Examine the electrical connectors, plugs, and pins for any moisture or corrosion. If moisture or corrosion is present, the component part must be replaced as per WIS instructions.
3. Leak Tightness Check: Seal all openings on the lamp with a product like Terostat IX and stabilize an overpressure of 40-50 mbar via the plug. If a sudden pressure drop occurs, indicating a leak, the component part must be replaced as per WIS instructions.

Important Warnings

• Do not wash the vehicle or subject it to high-pressure cleaning before the defogging test. This could interfere with the diagnostic process.
• It is not physically possible to defog the rear lamps completely; some residual fogging may remain. This residual fogging does not impair the functionality or service life of the rear lamps.
• External damage to the rear lamps does not constitute a warranty or goodwill case.

Owner Action

If you observe that the Mercedes-Benz AMG GT rear lamps fogged up, it's important to understand that minor condensation is often normal. However, if the fogging is excessive, persistent, or accompanied by other issues like visible damage or flickering lights, it is recommended to have your vehicle inspected by an authorized Mercedes-Benz service center. They can perform the diagnostic and repair procedures outlined in TSB LI82.10-P-078069 to determine if the lamp is defective or simply needs to be cleared of condensation.

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Source: NHTSA ID: 11010494