2021 Mercedes-Benz AMG GT Rear Lamp Fogging TSB

Symptoms

Owners of the 2021 Mercedes-Benz AMG GT may observe that their rear lamps appear fogged up or not leaktight. The official symptom description for this issue is "Lighting > Exterior lights > Driving lights > Taillamp > Fogged". While it might look concerning, Mercedes-Benz states that this condition, in many cases, does not impair the functionality or service life of the rear lamps.

Diagnosis and Trigger Conditions

Fogging in the rear lamps is often a natural occurrence, especially under certain climatic conditions. This TSB clarifies that some level of fogging is expected and does not necessarily mean the lamp is faulty. However, if the fogging is severe or persistent, technicians will perform specific diagnostic steps.

For the Mercedes-Benz AMG GT rear lamps fogged issue, the diagnosis involves:

• Visual Inspection: Checking for any external damage to the rear lamps.
• Aeration Cell Check: Ensuring that the differential aeration cells and diaphragm are present and correctly seated.
• Electrical Connector Inspection: Examining the electrical connectors of the plugs and pins for moisture or corrosion.
• Leak Tightness Test: Performing an overpressure test (40-50 mbar) by closing all openings with a sealant like Terostat IX to check for leaks.

Repair Procedure Summary

Mercedes-Benz outlines two main remedies for the Mercedes-Benz AMG GT rear lamps fogged issue, depending on the severity and cause of the condensation.

Remedy 1: Clearing Fogged/Condensed Rear Lamps

This procedure aims to clear existing condensation from the rear lamps without replacement. It involves several steps performed at the workshop:

1. Vehicle Preparation: The vehicle must be driven into a workshop where the temperature is higher than +18 °C (+64.4 °F). It is crucial not to wash the vehicle or subject it to high-pressure cleaning before this defogging test.
2. Power Management: The engine is switched off, and battery support is connected via a charger to maintain power during the process.
3. Access: The trunk is opened to allow air circulation.
4. Activation: The exterior lighting is switched on.
5. Drying Period: The vehicle is left in this state for 60 minutes.
6. Evaluation: After 60 minutes, the technician checks for a significant reduction in condensation, indicating successful defogging. It's important to note that some residual fogging may remain, as complete defogging is not always possible, and this does not impair functionality.

Remedy 2: Identifying Rear Lamps for Replacement

If the fogging persists after Remedy 1, or if other issues are found, the rear lamps may need replacement. This involves:

1. External Damage Check: Technicians inspect the rear lamps for any external damage. If damage is present, component parts must be replaced according to Mercedes-Benz Workshop Information System (WIS) instructions.
2. Electrical Connector Check: The electrical connectors are checked for moisture or corrosion. If found, the affected component parts must be replaced as per WIS instructions.
3. Leak Tightness Check: An overpressure test is performed. If there is a sudden pressure drop during this test, indicating a leak, the component part must be replaced as per WIS instructions.

Important Warnings

Owners should be aware of specific conditions related to this issue:

• Do not wash the vehicle or subject it to high-pressure cleaning before the defogging test. This can interfere with the diagnostic process.
• It is not physically possible to defog the taillamps completely – some residual fogging may remain. This residual fogging does not impair the functionality or the service life of the rear lamps.
• Simultaneous fogging of multiple component parts indicates extreme climatic conditions and also does not impair the functionality or the service life of the rear lamps.
• External damage to the rear lamps does not constitute a warranty or goodwill case. This means damage caused by external factors will likely not be covered under warranty.

Owner Action

If you observe your Mercedes-Benz AMG GT rear lamps fogged, it is recommended to visit an authorized Mercedes-Benz service center. They can perform the diagnostic and repair procedures outlined in TSB LI82.10-P-078069. Since this is a manufacturer communication, the repair may be covered under warranty if the condition is not due to external damage.

NHTSA ID: 11005294