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Dipped beam, detailed description

Dipped beam, detailed description

Dipped beam is lit when the light switch (10) is in position 2 and the ignition is on. The power supply to the dipped beam lamps is governed by the Underhood Electrical Centre (342). Dipped beam is used as daytime running lights in certain markets (light switch in position 0 or 1).


BCM (707) uses pins A29 and A30 to determine which position is set. BCM (707) pin A29 is connected to light switch pin 4, which corresponds to position 0. BCM (707) pin A30 is connected to light switch pin 2, which corresponds to position 2.

BCM (707) sends the bus messages "Dipped beam, button active ON", which is used by the fuse box in the engine bay (342). B+ voltage is supplied from fuse box pins 25 and 16 to headlamp pin 3.

Overvoltage protector

The fuse box outputs are protected from overvoltage. The maximum output voltage is 13.5 V. So average voltage does not exceed 13.5 V, the supply voltage to the lamps is PWM-regulated so that an average of 13.5 V is maintained. This protects the lamps from overload that would result in filament breakage. It also reduces heat build-up in the headlamps and light variation due to high voltage.


Filament monitor

In the event of filament breakage in a bulb, the electrical centre (UEC) detects the drop in current, regards it as a fault and sends a bus message which is used to display a message in SID. UEC supplies B+ to the lamps from a semiconductor output. If bulb output exceeds 100 W, a DTC is generated in UEC and an error message is displayed in SID.


Important

When changing a bulb, use one with the right output otherwise the components could be damaged.


Daytime Running Lights (DRL)

On certain markets, dipped beam is used as daytime running lights, which light automatically when the ignition is switched on.

DRL can be adjusted (ON / OFF) using the diagnostic tool. If the value is set to ON, dipped beam will come on when the light switch (10) is in position 0. If the value is set to OFF, neither parking lights nor dipped beam will come on when the light switch (10) is in position 0.

Limp-home

Dipped beam is lit if the following faults occur:



• UEC has no bus communication and ignition is on, lead from ISM (Ignition Switch Module) to UEC.

• Fault in UEC microprocessor.


Dipped beam is lit in the following cases:


• UEC receives bus message "Dipped beam, button active ON".

• BCM detects that the light switch is faulty.


Follow-me-home

When "Follow-me-home" is activated, dipped beam is lit in the front and the reversing lights or parking lights are lit in the back (which lights are lit is set using the diagnostic tool). This function is activated by removing the key from the ignition switch, opening the driver's door and pulling the main beam/dipped beam dipswitch back. The lights are lit for 30 seconds.


“Follow-me-home” means that the car lights are used when there are no other light sources.

A number of conditions must be fulfilled for BCM to activate this function:


- Key removed from ignition switch: BCM receives information via a bus message "Key position, ignition switch" from CIM (Column Integration Module) if the key is removed from the ignition switch. CIM receives information on pins 17, 18 and 23 from the ignition switch if the key is removed.

- Driver's door open: Voltage is supplied from the door switch to BCM pin 12 (LHD) or 11 (RHD) when the driver's door is open.

- Dipswitch activated: When the dipswitch (215) is activated, the bus message "Main beam, stalk active" is sent from CIM to BCM.