Daytime Running Lamp: Description and Operation

Twilight sentinel is a driver convenience that controls the exterior lamps in response to changes to the outside (ambient) light level. The twilight sentinel will also keep the exterior lamps on for a pre-selected period of time after the ignition is turned to the OFF position with nighttime conditions sensed. The exterior lamps will be turned off automatically after the relay period elapses. The delay period ranges 0 seconds to 3 minutes in approximately 12 second increments. The twilight delay switch in the headlamp switch is supplied a reference voltage from the HVAC control module W/C67 or Instrument Panel Module (IPM) W/CJ2. It is supplied a reference ground from the HVAC control module or IPM. The switch is a potentiometer that resistance varies as the switch is moved. The HVAC control module or IPM receives an input voltage proportional to the resistance of the potentiometer. The HVAC control module or IPM sends a class 2 message to the Dash Integration Module (DIM) indicating the on/off status and delay length for the twilight sentinel. With the twilight sentinel in an ON position, the DIM will automatically control the headlamps on/off status depending on the night time/daytime status of the sunload sensor. The DIM will use the twilight sentinel delay length to know how long to keep the headlamps and park lamps on after the ignition switch transitions from ON to OFF during night time conditions. The sunload sensor is a light sensitive transistor that varies its voltage signal to the HVAC control module or IPM in response to changes to the outside (ambient) light level. When the HVAC control module or IPM receives this signal, the HVAC control module or IPM sends a class 2 message to the DIM and to the Rear Integration Module (RIM). When the twilight switch is in ON, the DIM either turns on the DRL or turns on the low beam headlights, after a 20 second delay depending on whether daylight or low light conditions are sensed. Any function or condition that turns on the headlights will cancel the DRL operation. The FOG/DRL fuse in the underhood fuse block supplies battery positive voltage to the switch circuit of the Daytime Running Lamp (DRL) relay. Battery positive voltage is also supplied to the DRL relay control circuit from the underhood fuse block which is energized by the DIM. When the DIM energizes the DRL relay control circuit, the current flows from the switch contacts of the DRL relay to the left high beam. After the left high beam, the current flows through the left high beam fuse and through the right high beam fuse. The current continues through the right high beam to ground G401. The high beam headlamps are now in series, and split the voltage. The headlamps illuminate at half intensity. The DRL operate when the ignition switch is in the RUN position, and the parking brake is not set or the transmission is not in park. When these conditions have been met and the sunload sensor indicates daytime conditions, the DRL will illuminate.

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