4WD high range vs low range: when do I use each?
Use 4H when the surface is loose but you still need normal road-like speeds. Use 4L when the job requires slow control and more torque.
4H: grip without crawling
On a suitable part-time system, 4H supplies drive to both axles without low-range reduction. Whether to use it on a particular surface depends on the vehicle instructions and conditions. Extra driven wheels do not create extra braking grip or permission to travel at road speed on a rough track.
4L: control before momentum
Low range uses reduction gearing. The vehicle travels more slowly for a given engine speed and multiplies torque at the wheels. Use it for steep climbs and descents, rocks, deep sand, mud, ruts or controlled recovery—situations where you want fine throttle control and engine braking.
Source example: Ford Ranger Australian manual EB3B-19G219-CKB, June 2015, pp. 128–129. This historical edition illustrates mode restrictions; use the manual for your exact vehicle rather than its shift speeds.
One important warning
Most part-time 4WD systems should not be driven in 4H or 4L on dry, high-grip sealed roads. With no centre differential to absorb front-to-rear speed differences, the driveline can bind. Full-time 4WD and automatic 4A systems behave differently.
Shift procedures also differ. Some vehicles allow 2H-to-4H shifts while moving; selecting 4L commonly requires stopping and selecting neutral. Your owner’s manual wins every argument.
Use the transfer modes and shifting procedure specified in your vehicle owner's manual.