When your dashboard displays "Service 4-Wheel Drive" or "SVC 4WD," it means your vehicle's onboard computer has detected a fault in the four-wheel drive system. Unlike a routine maintenance reminder, this is a system warning indicating an actual problem requiring diagnosis. The issue could be as simple as a brief sensor signal drop, or it could indicate a failing component such as a shift motor, actuator, or transfer case switch. The message may appear even while you're driving in regular two-wheel drive mode, because modern 4WD systems constantly monitor all components in the background. Either way, it's a warning that deserves prompt attention from a qualified auto repair technician.