Automatic dimming outside mirror and inside rearview mirror, function - GF88.79-P-2010CE

WARNING: This page is about a different car, the 2011 Mercedes-Benz C350, 2010 Mercedes-Benz C350, 2009 Mercedes-Benz C350, and 2008 Mercedes-Benz C350. However, it is still accessible from the selected car via links, so may be relevant.

MODEL 204.0/2

with CODE (249) Automatically dimming inside rearview mirror and outside mirror (driver) as of model year 2009

/YoM 08

MODEL 204.3 with CODE (249) Automatically dimming inside rearview mirror and outside mirror (driver) MODEL 204.9

Function requirements general

Circuit 15R ON
Reverse gear not engaged
Interior illumination not switched on

The electronic ignition switch control unit (N73) transmits the status of circuit 15 via the interior CAN (CAN B).

Automatically dimming outside mirror and inside rearview mirror function sequence

The mirror glass on the inside rearview mirror (A67) and left outside mirror (M21/1) dims electrochromatically. This is realized by a layer of electrolyte gel in the mirror which controls the light permeability in increments depending on the voltage applied.

The inside rearview mirror senses the ambient light via the mirror dimming light sensor, forward (A67h1) and the light hitting the mirror glass via the mirror dimming light sensor, rearward (A67h2).

The inside rearview mirror evaluates these input variables and supplies dimming information via the wiper/inside rearview mirror LIN (LIN 2) to the front SAM control unit with fuse and relay module (N10/1), which sends the message for mirror dimming via the interior CAN.

The left door control unit (N69/1) receives the dimming information and supplies the corresponding actuation voltage to the mirror dimming (M21/1h1) of the left outside mirror. The inside rearview mirror is dimmed by actuation of the mirror dimming (A67h3).

If an interior lamp is switched on during mirror dimming or the reverse gear is engaged, the dimming is interrupted.

The status "Reverse gear engaged" is defined as follows depending on the transmission version:

Transmission 711 or 716:

The status of the backup (S16/2) lamp switch is read in directly by the front SAM control unit.

Transmission 722:

The request to "Engage gear range R" is defined by the corresponding selector lever position. The electronic selector lever control unit (N15/5) transmits the status of the current selector lever position to the front SAM control unit via the drive CAN (CAN C), CDI control unit (N3/9) (on diesel engine) or ME-SFI control unit (N3/10) (on gasoline engine) and chassis CAN.

Located in the front SAM control unit are two microprocessors, one for control of basic functions e.g. the exterior lights, and the second for control of the central gateway functions. Both processors communicate with one another internally via interior CAN.

The microprocessor for control of the central gateway functions uses the incoming information to generate the "reverse gear engaged" signal, which is independent of the transmission version, and sends this via wiper/interior LIN to the inside rearview mirror and via interior CAN to the left front door control unit.. Dimming of the inside rearview mirror and left outside mirror is canceled accordingly.

	Electrical function schematic for automatic mirror dimming	PE88.79-P-2052-97FAB
	Overview of system components for electric mirror	GF88.79-P-9996CE