Terraza FWD V6-3.5L VIN 8 (2005)
Daytime Running Lamp Control Unit: Description and Operation
AUTOMATIC LAMP CONTROL (ALC)
The normal headlamp switch operating position is AUTO, which enables the automatic lamp control (ALC). For ALC operation, the body control
module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient (outside) light level. The ambient light sensor is a light
sensitive transistor that varies its voltage signal to the BCM in response to changes to the ambient light level. The BCM uses multiple inputs to determine
daytime running lamp (DRL) or headlamp low/high beam operation. When the ignition key is turned to the RUN position the BCM determines the
light/dark ambient light condition and activates the headlamps or DRL mode immediately. When a transition to the light/dark ambient light condition
occurs after the ignition is in the RUN position there is an approximate 30-second delay in the headlamp/DRL transition.
The ALC System also has a defeat feature and a wiper activated headlamps feature. To operate the ALC defeat, turn the headlamp switch counter
clockwise one position past the AUTO position after starting the vehicle. This is a momentary switch position, and will return to the AUTO position.
This action sends a temporary ground signal to the BCM requesting a change of states for the ALC. If the ALC is currently ON it will switch to OFF, and
if the ALC is currently OFF it will reset the ALC to ON.
The wiper activated headlamps feature is enabled anytime the ALC is enabled. When the front windshield wipers have been activated for approximately
30 seconds, and the ALC is in the DRL mode, the BCM will switch to headlamps ON.
