Backup Lamp: Description and Operation

GF82.10-P-3011CA Backup Lamp Actuation, Function

Function requirements, backup 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).

Backup light actuation, general
The backup light actuation enables the traffic lane to the rear of the vehicle to be illuminated when backing up.

Backup lamp actuation function sequence
Vehicles with transmission 711, 716 (manual transmission): Engagement of the reverse gear is defined using the status of the backup lamp switch (S16/2), which is read in directly by the front SAM control unit.

Vehicles with transmission 722 (automatic transmission):
The request to "Engage gear range R" is defined by the corresponding selector lever position.
The electronic selector lever module control unit (N15/5) transmits the selector lever position via drive train CAN (CAN C), CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine) and chassis CAN (CAN E) to the front SAM control unit.

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 each other internally via interior CAN. The microprocessor for control of the central gateway functions uses all incoming information to generate the "Reverse gear engaged" signal that is independent of the type of transmission and sends this via interior CAN to the rear SAM control unit with fuse and relay module (N10/2) and, in vehicles with code (550) Trailer hitch, to the trailer recognition control unit (N28/1).

The rear SAM control unit receives this signal and actuates the left backup lamp (E3/1e3) and the right backup lamp (E4/1e3). The trailer recognition control unit receives this signal and actuates the backup lamp on the trailer via the trailer socket (X58).

To prevent any brief illumination of the backup lamps in vehicles with transmission 722 when changing from gear range "P" to "D" via "R", the request from the front SAM control unit is sent with a delay of t = 500 ms.