Brake Lamp: Description and Operation

GF82.10-P-3010CA Brake Light Actuation, Function

Function requirements, brake light actuation, general
^ No overvoltage or undervoltage
(operating voltage range U ≥ 7 ≤17.5 V)
^ Circuit 15 ON

The electronic ignition switch control unit (N73) transmits circuit 15 status to the front SAM control unit with fuse and relay module (N10/1) via the interior CAN (CAN B).

Brake light actuation, general
Corresponding to the request the brake light actuation realizes a static or flashing actuation of the brake lights on the vehicle.

Brake light actuation is comprised of the following subfunctions:
^ Function sequence, static brake lights
^ Function sequence, adaptive brake lights

Function sequence, static brake lights
The brake light switch (S9/1) is supplied with circuit 15 by the front SAM control unit. When the service brake is actuated, the voltage present is transmitted to the Electronic Stability Program control unit (N30/4) (without code (233) DISTRONIC PLUS) or to the Electronic Stability Program Premium control unit (N30/7) (with code (233) DISTRONIC PLUS). The Electronic Stability Program control unit generates the brake light actuation request from this, and makes it available on the chassis CAN (CAN E).

The front SAM control unit receives the request and relays it via the interior CAN to the rear SAM control unit with fuse and relay module (N10/2) and with vehicles with code (550) Trailer hitch additionally to the trailer recognition control unit (N28/1).

The Electronic Stability Program control unit also actuates the rear SAM control unit and the trailer recognition control unit via a direct line (circuit 54), to counteract any delay in the forwarding of the request via the two data buses.

The rear SAM control unit receives the request and actuates the following components:
- Outer left brake light and taillight (E3e11)
- Inner left brake light and taillight (E3/1e4)
- Outer right brake light and taillight (E4e11)
- Inner right brake light and taillight (E4/1e4)
- Center brake lamp (E21)

The trailer recognition control unit receives the request and actuates the brake lights of the trailer via the trailer socket (X58).

Additional function requirements, adaptive brake lights
^ Vehicle speed v > 25 km/h
^ Brake Assist system active or vehicle deceleration a > 7.5 m/s2

Function sequence, adaptive brake lights
The instrument cluster (A1) transmits the vehicle speed via interior CAN to the front SAM control unit.
In the event of emergency braking, the Electronic Stability Program control unit transmits an appropriate signal to the front SAM control unit via the chassis CAN.
The front SAM control unit forwards this signal via interior CAN to the rear SAM control unit and in vehicles with code (550) Trailer hitch to the trailer recognition control unit.

The rear SAM control unit actuates the brake lights and center brake light for the duration of the signal (t ≥1 s) at a frequency of f = 3 to 5 Hz and also sends a corresponding signal via the interior CAN to the trailer recognition control unit, which defines the time duration for the dark phase set.

The following frequencies are output, depending on the light sources used on the trailer:
- for incandescent bulbs, f = 3 Hz
- for light emitting diodes (LEDs), f = 5 Hz

If the vehicle comes to a standstill following emergency braking, the hazard warning flasher function is always automatically activated if braking occurred from a speed of v > 70 km/h.

The danger braking signal is reset if one of the following preconditions is met:
- Vehicle speed v < 10 km/h
- Vehicle deceleration a < 6.5 m/s2