Why Is My Semi Truck ABS Light On?

Why Is My Semi Truck ABS Light On?
An illuminated ABS light on a semi truck means the anti-lock braking system has detected a fault and temporarily disabled itself. While your service brakes still work, ABS assistance is lost—reducing control during hard braking or low-traction conditions and potentially leading to DOT citations. The most common causes include dirty or misaligned wheel speed sensors, damaged wiring or connectors, blown ABS fuses, and trailer electrical issues at the 7-way plug or pigtail. Intermittent ABS lights usually point to wiring or connection problems that worsen over time. The correct fix starts with basic inspections and diagnostics to identify the root cause and safely restore full braking performance.