The twilight sentinel performs 2 major functions. The twilight sentinel determines the automatic turn on/off control of the exterior lamps. It also holds the exterior lamps on for a period of time after the ignition switch is removed from the RUN position.

When the twilight sentinel is enabled, the instrument cluster twilight enable input is grounded via CKT 1784 (YEL/BLK) through the headlamp switch. When the ignition switch is in the RUN position, the ambient light indicates darkness, and the twilight sentinel is enabled, the instrument cluster sends a request via the Class 2 serial data line to the body control module (PZM) to activate the low beam headlamps. The PZM then applies battery positive voltage (B+) to the coil of the headlamp relay. The PZM also provides ground for the coil via CKT 10 (YEL). The low beam headlights are then activated as previously described when activated with the headlamp switch. The park lamps are also illuminated.

The instrument cluster will display a HEADLAMPS SUGGESTED message when all of the following conditions are present:

If the exterior lamps are illuminated due to an automatic turn on by the twilight sentinel, the twilight sentinel will keep the headlamps and park lamps on for a driver defined delay period when the ignition switch is removed from the RUN position. Activation of the headlamp switch will override all twilight sentinel operations.

The setting of the twilight delay control in the headlamp switch determines the twilight delay (lamps time-out) after the ignition switch is removed from the RUN position. The instrument cluster monitors the twilight delay input through CKT 1783 (PPL). The value of the input voltage will be between 0 and 5 volts. When the twilight delay control is moved from the MIN to the MAX position, the voltage input increases. The instrument cluster adjusts the twilight delay in 10 second intervals from 3 to 180 seconds in response to the voltage level at the twilight delay input. If the twilight sentinel is turned off during the delay period, the headlamps and the park lamps will turn off immediately.