Brief description of components

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The following components and control units provide input signals for the adaptive headlights system:

Light switches on the light switch cluster
The rotary switch for the side lights and dipped beam headlights differs depending on the vehicle equipment level (adaptive headlights, automatic driving lights control, automatic or manual headlight-range adjustment). For the adaptive headlights function to operate, the light switch must be set to position "A" ("A" = "automatic driving lights control" or "adaptive headlights"). For more information, refer to E46 LIGHT SWITCH ON THE LIGHT SWITCH CLUSTER .
Direction indicator/main beam switch
The main beam headlights are switched on and off with the direction indicator/main beam switch (by pressing or pulling the switch). The adaptive headlights function operates with both dipped and main beam headlights. For more information, refer to E46 - DIRECTION INDICATOR/MAIN BEAM SWITCH .
Ride-height sensors
The ride-height sensors supply the input signals for the headlight-range adjustment. There is one ride-height sensor located on the right-hand side of the front axle. There is one ride-height sensor located on the right-hand side of the rear axle.

Automatic headlight-range adjustment adjusts the vertical aim of the headlights to compensate for variations in the vehicle tilt angle (e.g. when the vehicle is laden, and under braking and acceleration when the vehicle is in motion).

If the vehicle is equipped with the "adaptive headlights" option, the control unit analyses the signals from the ride-height sensors for the adaptive headlights (AHL control unit).

This is because: The AHL control unit also controls automatic headlight-range adjustment. For more information, refer to E46 RIDE-HEIGHT SENSORS .
Brake light switch
If the vehicle is equipped with the "adaptive headlights" option, the signals from the brake light switch are read by the control unit for the adaptive headlights.

The signal sent by the brake light switch is an input signal for the automatic headlight range adjustment; see RIDE-HEIGHT SENSORS.
Zero-position sensor (E46, E63, E83)
The zero-position sensor in the AHL headlight sends a signal for calculating the zero position of the AHL headlight. This regulates the horizontal movement of the AHL headlight. For more information, refer to E46, E63, E64, E83, E90 - ZERO-POSITION SENSOR .
Basic module
The basic module supplies input signals with regard to the terminal management (terminal 15 ON).

The adaptive headlights control unit is activated when terminal 15 is switched ON.
EGS control unit or reversing light switch
When reverse gear is engaged, the headlights are moved to the straight-ahead position.

For automatic transmissions, the EGS (electronic transmission control) sends the appropriate signal to the light module; for manual transmissions, the reversing light switch sends the signal.
KOMBI (control unit in the instrument cluster):
The instrument cluster control unit is the gateway (i.e. data interface) between the PT CAN data bus and the K bus. The signals from the EGS control unit and the DSC control unit (see below: DSC sensor) are sent via the KOMBI control unit to the control unit for the adaptive headlights.
Rain-light sensor for automatic driving lights control (option)
The rain-light sensor measures the ambient light conditions outside the vehicle.
- In twilight, the rain-light sensor sends the request "Twilight" to the light switch cluster. The light switch cluster sends the relevant information to the adaptive headlights control unit which enables the automatic headlight-range adjustment of the dipped beam headlights to be activated. The headlights are tilted up and down as required, but they are not swivelled towards the bend in the road.
- In darkness, the rain-light sensor sends the message "Darkness" to the light switch cluster. The light switch cluster sends the relevant information to the adaptive headlights control unit. The headlights are swivelled towards the bends in the road as required. For more information, refer to E46 - RAIN-LIGHT SENSOR .
Steering angle sensor and DSC sensor
The steering angle sensor and DSC sensor (DSC = Dynamic Stability Control) supply signals for the adaptive headlights to the adaptive headlights control unit. These signals are evaluated as follows, depending on the vehicle's speed:
- Vehicle speeds up to 30 km/h:
  The adaptive headlights function is controlled on the basis of the information from the steering angle sensor (in the steering column switch cluster).
- Vehicle speeds between 30 km/h and 50 km/h:
  In the 30 to 50 km/h speed range, there is a continuous transition in signal evaluation: from the evaluation of signals sent by the steering angle sensor to evaluation of the signals sent by the yaw rate sensor (in the DSC sensor).
- Signals from the yaw rate sensor are evaluated in extreme dynamic driving situations , e.g. if the vehicle starts to skid or fishtail, even at speeds of less than 50 km/h.
  If the vehicle starts to skid or fishtail, the headlights will move to the straight-ahead position. The headlights are not swivelled until the vehicle has stabilized.
- Vehicle speeds over 50 km/h:
  At speeds upwards of 50 km/h, the signals from the yaw rate sensor (in the DSC sensor) form the primary basis for control of the adaptive headlights function.
  
  Reason: for a constant cornering radius, the steering angle required increases over proportionally with increasing speed. In addition, the steering angle required also depends on the friction coefficient of the carriage way.
  
  The yaw rate is directly proportional to speed. For this reason, the yaw rate is always the most suitable measure for controlling the adaptive headlights at high speeds.
  
  Even at high speeds, however, the steering angle sensor signal is used to detect in advance (predict) the driver's commands. This is because: The yaw rate signal is not supplied until the vehicle has responded to the steering wheel movement.
  
  There is no signal output by steering angle sensor in the event of sudden, rapid steering wheel movements (surging) to prevent these from influencing the function of the adaptive headlights.
A number of control units are involved in the adaptive headlights system (see GM, EGS, KOMBI).

In a narrower sense, the following control units are involved in the adaptive headlights function:
AHL control unit
For safety reasons, the AHL control unit is also responsible for the automatic headlight range adjustment.

The following fault is conceivable: after swivelling, one headlight remains in a position that is dazzling to oncoming traffic. As a result, the AHL control unit attempts to tilt this headlight downwards (using the stepper motors for the automatic headlight-range adjustment).

If the headlight cannot be tilted downwards, the bi-xenon bulb in this headlight is disabled.

Conditions for disablement: The vehicle must have been parked (vehicle stationary and terminal R OFF for several minutes).

The AHL control unit is connected to the K bus. For more information, refer to E46 - AHL CONTROL UNIT FOR ADAPTIVE HEADLIGHTS .
Stepper motor controllers
The stepper motor controllers (SMC) control the stepper motors in the headlights (for the automatic headlight-range adjustment and for the adaptive headlights)., For more information, refer to E46 STEPPER MOTOR CONTROLLERS .
LSZ control unit
The LSZ control unit (light switch cluster) forwards requests from the light switch and the direction indicator/main beam switch to the AHL control unit (on the K bus). For more information, refer to E46 LSZ CONTROL UNIT .
Xenon-headlight control unit
The xenon-headlight control unit monitors the D2-S bulbs for the bi-xenon headlights. For more information, refer to E46 - BI-XENON HEADLIGHTS .

The following components are controlled:
Stepper motors for the adaptive headlights
Are located in the headlight units. For more information, refer to E46 - HEADLIGHTS .

The stepper motors turn the swivel modules in the bi-xenon headlights.

The stepper motors swivel the headlights along the vertical and horizontal axes. (vertical = up and down for the automatic headlight-range adjustment;

horizontal = to the left and right for the adaptive headlights).
Green indicator light on the light switch cluster
The green indicator lamp next to the "A" ("A" stands for "Automatic driving lights control" or for "Adaptive headlights") has two display functions:
- The LED lights up permanently when the automatic driving lights control/adaptive headlights function is switched on (= light switch in position "A").
- The LED flashes if a fault develops in the adaptive headlight system. For more information, refer to E46 - ADAPTIVE HEADLIGHTS (AHL), DIAGNOSTICS .
The green indicator lamp (LED) is actuated by the light switch cluster.

NOTE: Components for the AHL on the E53

Similarities with the E46: The E53 has the same vehicle electrical system as the E46. The E53 uses the LSZ (light switch cluster) control unit for controlling the exterior lights (as does the E46).
Similarities with the E60: The E53 has a position sensor (as does the E60) instead of a zero-position sensor (= E46).

NOTE: Components for the AHL on the E63

Similarities with the E60: The E63 has the same vehicle electrical system as the E60. The E63 uses the LM (light module) control unit for controlling the exterior lights (as does the E60).
Similarities with the E46: The E63 has a zero-position sensor (as does the E46).