Circuit/System Description

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The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a 5 V reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL resistor via the DRL resistor control circuit. When the BCM applies ground to the DRL resistor control circuit, the DRL signal circuits to the right and left headlamp assemblies are pulled low. The DRL signal circuits are direct inputs to the right and left headlamp control modules. When the DRL signal circuits are provided with ground, the right and left headlamp control modules respond by turning OFF the low beam headlamps and activating the DRLs. Any function or condition that turns the headlamps ON will cancel DRL operation.