Mercedes-Benz bulletin LI82.10-P-078069

Complaint Rear lamps fogged up/not leaktight. Cause Fogging of the rear lamps is a natural phenomenon, which can occur under certain climatic conditions. This does not lead to any technical impairment of the rear lamps. Remedy Rear lamp: Remedy 1: Clearing fogged/condensed rear lamps: 1. Drive the vehicle into the workshop (temperature higher than +18 °C/+64.4 °F) Note: Do not wash the vehicle or subject it to high-pressure cleaning before the defogging test. 2. Switch off the engine and connect battery support via a charger. 3. Open the trunk. 4. Switch on the exterior lighting. 5. Leave the vehicle in this state for 60 minutes. 6. Check for formation of condensation -> a significant reduction in the formation of condensation must be clearly recognizable (defogging progress). Note: -If no reduction in the degree of fogging is visible, the rear lamp is defective and must be replaced. -It is not physically possible to defog the headlamps completely – some residual fogging may remain. 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. Remedy 2: You can recognize a defective rear lamp as follows: 1. Check the rear lamps to ensure that no external damage is present, and that the differential aeration cells and the diaphragm are present and correctly seated. -> If there are signs of external damage on the rear lamp, the component parts must be replaced as per WIS instructions. 2. Check the electrical connectors of the plugs and pins. -> If moisture/corrosion/etc. is present, the component part must be replaced as per WIS instructions. 3. Check for leak tightness -> Close all openings with Terostat IX or similar and establish and stabilize via an overpressure (40–50 mbar) via the plug. -> In the event of a sudden pressure drop, the component part must be replaced as per WIS instructions. Note: External damage to the rear lamps does not constitute a warranty or goodwill case.

Owners of the 142 model years this bulletin names have filed 4,433 complaints with NHTSA since 2015. 138 of them name Visibility/Wiper, Exterior Lighting — the same broad component group this bulletin is filed under. NHTSA groups complaints coarsely, so that means the same area of the vehicle, not necessarily the same fault.

On the 2016 Mercedes-Benz C-Class, the 15 owners who gave an odometer reading for Visibility/Wiper reported it at a median of 40,000 miles. That figure is one model year’s, not the whole range this bulletin covers — medians from different model years are not averaged.