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Rear fog light, detailed description

Rear fog light, detailed description

The rear fog light is located in the light cluster (418) housed in the boot lid, on the left-hand side on cars intended for right-hand traffic and on the right-hand side on cars intended for left-hand traffic.


The fog light is activated with the rear fog light switch (161/684). The instantaneous-type switch is connected to BCM pin A7(K78). The input has diagnostics.

The switch grounds BCM pin A7(K78) when the switch is pressed. BCM sends a bus message used by the Rear Electrical Centre (REC). REC (701) pin 2(T-C) supplies voltage to the rear fog light bulb, which lights.


If the ignition is on and the button on the switch (161) is pressed, the BCM input (707) is grounded and BCM sends the bus message "Rear fog light, button active ON". REC (701) reads the bus message and activates output pin 2 (T-C) to the rear fog light (33HL/33HR) if the front fog lights or main/dipped beam are lit. The light cluster (418HL/HR) pin 2 is grounded in grounding point G3, the lead goes via REC to ground.

Conditions for rear fog light activation:


• Ignition in ON position

• Rear fog light, button active

• Front fog lights or main/dipped beam on


If one of the above conditions is no longer fulfilled, the rear fog light goes out. When the rear fog light is lit, REC (701) sends the bus message "Rear fog light, indicator active ON", which is used by MIU to light the rear fog light symbol.

So as not to load the battery any more than necessary, UEC switches off the rear fog light when the starter motor is activated.

Filament monitor

In the event of a break in the rear fog light circuit, REC (701) sends the bus message "Rear fog light not working ON". This bus message is used by SID, which displays an error message to the driver.


Important

When changing a bulb, use a replacement bulb of the correct wattage, since there could otherwise be damage to components.