das hab ich gerade gefunden, scheint also tatsächlich da zu sitzen:
AUTOMATIC HEADLAMPS
The optional automatic headlamp (auto low) system includes the Steering Control Module (SCM), the Front Control Module (FCM), the left (lighting) multi-function switch and, depending upon vehicle equipment either the sun load sensor on the top of the instrument panel or the Rain Sensor Module (RSM) on the inside of the windshield below the electrochromic inside rear view mirror mounting button. First, the Auto Low option must be enabled using the customer programmable features function of the Electronic Vehicle Information Center (EVIC). Then the A (Automatic) position must be selected using the left multi-function switch.
Once these prerequisites have been met, the SCM responds by sending the appropriate electronic lighting request messages to the FCM over the Controller Area Network (CAN) data bus and, either the sun load sensor provides an ambient light level input to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) which is relayed to the FCM over the CAN data bus, or the RSM provides electronic ambient light level messages to the FCM over the CAN data bus. With the engine running, the FCM responds to these messages by automatically controlling a pulse width modulated voltage output to the selected headlamp bulbs through the right and left low beam feed circuits to illuminate the headlamps. The FCM also sends the appropriate electronic messages back to the EMIC to control the illumination of the high beam indicator.
