What is the issue when both 4H and 4L lights illuminate together?

[LeonardoFitz]

When both the 4H and 4L lights illuminate together, it indicates a fault in the four-wheel drive system that requires inspection and repair. Introduction to Four-Wheel Drive Systems: It enables all four wheels of the vehicle to receive driving force. The engine's power is distributed to all four wheels, significantly reducing wheel slippage on poor road conditions and greatly improving the vehicle's off-road capability. Classification of Four-Wheel Drive Systems: Part-Time 4WD and Full-Time 4WD. Part-Time 4WD can operate in two modes: one is two-wheel drive, where only two wheels receive power, similar to a conventional vehicle; the other is four-wheel drive, where the front and rear axles distribute power equally in a 50:50 ratio. Full-Time 4WD is a system where all four wheels continuously maintain driving force.