Headlamp control, function

Function requirements, general

 No overvoltage or undervoltage (operating voltage range from 11.0 to 15.5 V)

Driving lights actuation, general

Driving lights actuation includes all functions which serve the optimum illumination of the road while driving.

The driving lights actuation encompasses the following subfunctions:

 Function sequence for low beam actuation

 Function sequence for high beam actuation

 Function sequence for daytime running lights actuation

 Function sequence for auto on/off driving lights

 Function sequence for headlamp range adjustment (HRA [LWR])

 The electronic ignition lock (EZS) control unit (N73) sends the status of circuit 15 via interior CAN (CAN B) to the signal acquisition and actuation module (SAM) control unit (N10/1).

 The driving lights are actuated corresponding to the position of the illumination switch (S1/2). The signal acquisition and actuation module (SAM) control unit directly reads in the status of the illumination switch.

Additional function requirements for low beams actuation

 Circuit 15 ON

 During low beams actuation, the standing light actuation is active, this is described in the "Standing/parking lights actuation function" document.

Function sequence for low beam actuation

Turning the illumination switch into the "low beams" position requests actuation of the low beams.

The signal acquisition and actuation module (SAM) control unit directly reads in the status of the illumination switch and sends a request for switching on the low beams via interior CAN, electronic ignition lock (EZS) control unit and front end CAN (CAN G) to the left headlamp control unit (E1/1n9). Via the left headlamp LIN (LIN G1) and left front actuation module, LED exterior lighting (E1/1n7), it then actuates the left low beam (short range) (E1/1e15) and the left low beam (long range) (E1/1e16).

The signal acquisition and actuation module (SAM) control unit also sends a request for switching on the low beams via interior CAN, electronic ignition lock (EZS) control unit and front end CAN to the right headlamp control unit (E2/1n9). Via the right headlamp LIN (LIN G2) and right front actuation module, LED exterior lighting (E2/1n7), it then actuates the right low beam (short range) (E2/1e15) and the right low beam (long range) (E2/1e16).

The signal acquisition and actuation module (SAM) control unit also sends the "Low beams indicator lamp" request via interior CAN, gateway for user interface CAN (N93/4) and user interface CAN (CAN HMI) to the instrument cluster (IC) control unit (A1/1), which then actuates the low beams indicator lamp (A1/1e67).

Additional function requirements for high beam actuation

 For high beams function: circuit 15 ON and low beams ON

 For headlamp flasher function: Circuit 15R On

Function sequence for high beam actuation

The high beams actuation is comprised of the following subfunctions:

 Function sequence for high beams

 Function sequence for headlamp flasher

Function sequence for high beams

High beam actuation is requested by pushing the combination switch (S4) forward.

The steering column tube module (MRM) control unit (N80) directly reads in the switch position of the combination switch and sends this via the chassis CAN (CAN E), electronic ignition lock (EZS) control unit, and interior CAN to the signal acquisition and actuation module (SAM) control unit.

The signal acquisition and actuation module (SAM) control unit sends the "High beams On" request via interior CAN, electronic ignition lock (EZS) control unit and front end CAN to the left headlamp control unit and to the right headlamp control unit. The left headlamp control unit then actuates the left low beam (long range) via left headlamp LIN and left front actuation module, LED exterior lighting. At the same time, the right headlamp control unit actuates the right low beam (long range) via right headlamp LIN and right front actuation module, LED exterior lighting. The low beams (long range) then generate the high beams. The left high beam (E1/1e1) and the right high beam (E2/1e1) are also switched on if necessary.

The signal acquisition and actuation module (SAM) control unit also transmits a "High beams indicator lamp" request via the interior CAN, the user interface CAN gateway and the CAN user interface to the instrument cluster (IC) control unit, which then actuates the high beams indicator lamp (A1/1e3).

Function sequence for headlamp flasher

The function sequence and signal path for the headlamp flasher function correspond to that of the high beam function. However, to request the headlamp flasher function, the combination switch must be pulled backward. If the combination switch is pulled back and held, the high beam actuation is active for maximum 30 s. Then the pending request is interpreted as a "stuck combination switch" and the actuation of the high beams is terminated.

Additional function requirements for daytime running lights actuation

 "Daytime running lights" function activated in instrument cluster (IC) control unit

 "Engine running" signal set and vehicle speed > 3 km/h

 Illumination switch in "AUTO" position

Function sequence for daytime running lights actuation

The instrument cluster (IC) control unit transmits the request for switching on the daytime running lights via the user interface CAN, the gateway for user interface CAN and the interior CAN to the signal acquisition and actuation module (SAM) control unit.

The CDI control unit (N3/33) or the ME-SFI [ME] control unit (N3/34) (with engine 274) sends the "engine running" signal via chassis CAN, electronic ignition lock (EZS) control unit and interior CAN to the signal acquisition and actuation (SAM) control unit.

The Electronic Stability Program (ESP) control unit (N30/4) sends the vehicle speed via the chassis CAN, electronic ignition lock (EZS) control unit and interior CAN to the signal acquisition and actuation module (SAM) control unit.

The signal acquisition and actuation module (SAM) control unit evaluates all relevant information and sends a request for switching on the daytime running lights via interior CAN, electronic ignition lock (EZS) control unit and front end CAN to the left headlamp control unit and to the right headlamp control unit.

The left headlamp control unit then actuates the daytime running lights in the left parking/standing/daytime running light (E1/1e13) via left headlamp LIN and left front actuation module, LED exterior lighting.

At the same time, the right headlamp control unit actuates the daytime running lights in the right parking/standing/daytime running light (E2/1e13) via right headlamp LIN and right front actuation module, LED exterior lighting.

The daytime running lights actuation is deactivated as soon as the illumination switch is turned to the standing light, manual driving lights, left parking light or right parking light position.

Additional function requirements for auto on/off driving lights

 "Engine running" signal set and vehicle speed > 3 km/h

 Illumination switch in "AUTO" position

The CDI control unit or ME-SFI [ME] control unit transmits the "Engine running" signal via the chassis CAN, the electronic ignition lock (EZS) control unit and the interior CAN to the signal acquisition and actuation module (SAM) control unit.

The Electronic Stability Program (ESP) control unit transmits the vehicle speed via the chassis CAN, the electronic ignition lock (EZS) control unit and the interior CAN to the signal acquisition and actuation module (SAM) control unit.

Function sequence for auto on/off driving lights

In the auto on/off driving lights, the low beams are automatically switched on or off.

The auto on/off driving lights are purely a comfort function and do not relieve the driver of the need to follow the operating instructions as prescribed by the road traffic regulations.

The low beams are switched on or off depending on the ambient brightness or depending on the activities of the windshield wiper system:

 Function sequence for auto on/off driving lights via humidity sensor/light sensor/rain sensor (B38/2) (with code HH9 (Semi-automatically controlled air conditioning, TEMPMATIC)) or via humidity sensor/light sensor/rain sensor/sun sensor (B38/3) (with code HH4 (THERMOTRONIC automatic air conditioning))

 Function sequence for auto on/off driving lights over wiper activities

Function sequence for auto on/off driving lights via humidity sensor/light sensor/rain sensor (B38/2) (with code HH9 (Semi-automatically controlled air conditioning, TEMPMATIC)) or via humidity sensor/light sensor/rain sensor/sun sensor (B38/3) (with code HH4 (THERMOTRONIC automatic air conditioning))

The ambient brightness is detected by the humidity sensor/light sensor/rain sensor or humidity sensor/light sensor/rain sensor/sun sensor. This transmits a signal to the signal acquisition and actuation module (SAM) control unit via the roof LIN (LIN B13). The signal acquisition and actuation module (SAM) control unit evaluates this signal and activates the low beams actuation.

 If the humidity sensor/light sensor/rain sensor or the humidity sensor/light sensor/rain sensor/sun sensor fails, the auto on/off driving lights are not deactivated until the engine is switched off.

 When the vehicle is being driven through a tunnel and if the wiper start suppression function is active, the auto on/off driving lights function remains switched on.

Function sequence for auto on/off driving lights over wiper activities

If the low beams are switched on or off due to the activities of the windshield wiper system, one refers to adverse weather light. The signal acquisition and actuation module (SAM) control unit controls the windshield wiper system.

If the windshield wiper system is activated for more than 20 s with a wipe cycle time of less than 6 s, the signal acquisition and actuation module (SAM) control unit activates the low beams actuation. If there are no wipe cycles for 60 s, low beams actuation is deactivated.

 If the wiper startup suppression function is canceled, the auto on/off driving lights remain active for an additional 60 s. Detailed information on the wiper startup suppression function can be found in the document "Windshield wipe, function".

Additional function requirement for headlamp range adjustment (HRA)

 Driving lights ON (low beam or high beam)

Function sequence for headlamp range adjustment (HRA [LWR])

The automatic HRA [LWR] corrects the headlamp range of the vehicle headlamps in accordance with the load and the vehicle pitch motions caused by the vehicle dynamics.

The left headlamp control unit directly reads in the signals from the front axle level sensor (B22/2) and the rear axle level sensor (B22/3) and evaluates them. The left headlamp control unit then directly actuates the left headlamp range adjustment actuator motor (E1/1m1) and the right headlamp range adjustment actuator motor (E2/1m1).

If the vehicle is moving at a constant speed, the automatic headlamp range adjustment system operates in "static mode" at a low adjustment speed. When the vehicle is accelerated, the "dynamic mode" is activated and the reaction time of the automatic headlamp range adjustment is significantly reduced. The "dynamic mode" is activated depending on the speed change and additional signals from the brake and accelerator pedal positions.

 When the vehicle is standing automatic headlamp range adjustment is accomplished in the "dynamic mode".