Automatic dimming of exterior and interior rearview mirrors, function - GF88.79-P-2010T

MODEL 211.0/2 with CODE (249b) Automatic dimming of interior and exterior rearview mirrors (driver's side) 

Fig 1: Automatic Dimming Of Exterior And Interior Rearview Mirrors Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function prerequisites 

• Circuit 15R ON or
• Circuit 15 ON
• No overvoltage or undervoltage
• Reverse gear not engaged
• Vehicle interior lighting off

Function 

The mirror lens in the exterior rearview mirror on the driver's side and the interior rearview mirror are dimmed electrochromatically. For this purpose, a layer of electrolytic gel is located in the mirror lens between the reflector and glass cover. When a voltage is applied to this electrolytic gel, it changes its translucency. The light hitting the surface of the mirror is more or less reflected due to the variable of the actuation voltage.

The actuating voltage is controlled by the interior rearview mirror unit (A67) and overhead control panel control module (N70). Control is accomplished depending on the relationship between the ambient light and the light hitting the mirror lens.

These two factors are measured by the automatic dimming mirror sensor toward front (A67h1) and toward rear (A67h2) in the interior rearview mirror unit (A67) and sent discreetly to the overhead control panel control module (N70) which relays the dimming information to the CAN, class B bus.

The left front door control module (N69/1) evaluates the dimming information and supplies the appropriate actuating voltage to the mirror dimming control (M21/1h1).