The headlamp input signal wire is broken or disconnected, so the body control module can't detect whether the headlamps are on or off. Think of it like a light switch with a severed wire—the switch works, but nothing receives the signal.

The body control module (BCM) monitors the headlamp input circuit for a valid voltage signal (typically 12V when headlamps are on, 0V when off). When the circuit is open, the module detects an abnormal high-impedance state and cannot distinguish headlamp status. The BCM uses this signal for automatic light control, daytime running lights, and light-off reminder functions.

Voltage & Parameter Thresholds