Envoy 2WD V6-4.3L VIN W (1998)
Data
Range: 0-5.0 volts
The displayed voltage value refers to the amount of ambient light level as measured by the light sensor. This information is used by the BCM in order to
operate the automatic headlamp feature and the Daytime Running Lamps (DRL) feature. The BCM supplies 5 volts to the ambient light photocell sensor
and receives a return signal voltage from the ambient light photocell on the return signal circuit. The ambient light sensor internal resistance changes
with different levels of ambient light. In LIGHT ambient conditions, the resistance is low. In DARK ambient conditions, the resistance is high.
The BCM interprets the following conditions as LIGHT:
^
The ambient light sensor is exposed to bright ambient light (low resistance).
^
High voltage (2.2-4.7 volts) is present on the return circuit.
The BCM interprets the following conditions as DARK:
^
The ambient light sensor is exposed to dark ambient light.
^
Internal resistance increases.
^
The return signal voltage decreases (0.2-1.3 volts).
If there is an open or a short to ground in the ambient light sensor circuit, the sensor will read about 0.0 volts. The BCM will default into a DARK state
and turn ON the headlamps.
If the headlamps are set to the AUTO position while in the LIGHT state and the ambient light level conditions change to DARK for 15 seconds, the
BCM will turn ON the headlamps.
If the headlamps are set to the AUTO position while the DARK state and the ambient light level conditions change to LIGHT for 20 seconds, the BCM
will turn the headlamps OFF.
Ambient Light
