When 4WD is engaged, the engine sends power to the transmission, which is then split into the front and wheel axles. The torque gets transferred to the wheels, but the wheels must have traction on the road in order for the vehicle to move anywhere.
Do all 4 wheels turn in 4 wheel drive?
A 4WD vehicle that has two locking differentials provides true 4WD — all four wheels turn with the same amount of power no matter the situation. Even if the wheels on one side of your vehicle are completely off the ground, the wheels that are still on the ground will still continue to get a steady amount of torque.
Does 4 wheel drive hurt your car?
There is low to no risk of mechanical damage by parking your vehicle in 4 wheel drive mode overnight. Leaving your truck in 4WD mode when surface traction is limited, such as snow, sand, or ice, could be advantageous as it decreases the potential of the vehicle losing traction.