Hill-descent control gives off-roaders a new tool for tackling steep, slippery hills. The system combines the low gearing traditionally used in such situations with automatic braking by the computer to keep the vehicle moving slowly while making sure it's pointed straight down the hill. Getting sideways while sliding down a steep grade is often a one-way ticket to a rollover, so keeping the wheels going the right way is critical. It's even easier to get crossed up when backing down a hill after an unsuccessful hill climb, and the same system works in reverse.
Once only available on high-dollar Land Rovers, hill-descent control now is available on more affordable models. The only problem with such a system is that its use takes an act of faith: Driving down a hill without your foot on the brake (after pressing the button to activate the system) can be unnerving. Touching the brake typically deactivates it, once again giving the driver direct control. Using the system properly means laying off the brakes in situations that appear to demand their use. But first you have to trust the truck won't start racing downhill.
The LR3 Terrain Response 4WD system uses a series of sensors to change ride height, locking differential settings (front, rear, center), transmission gearing, throttle response, and more, depending on the type of terrain you need to navigate. This is probably the most advanced electronic traction system available on any 4x4.
Calibrations vary from one manufacturer to another, but they typically limit downhill speed to 2-4 mph. Nissan's system works in high and low range, with a higher descent speed of 6.7 mph in high range, according to Jeff Ceccacci, Xterra and Pathfinder product planner.
Another trail-ride circumstance electronics can help with is the dreaded uphill stall. Getting started again without too much backward roll is important (and especially difficult when driving a manual transmission), because there might be something behind you that you could hit, or you may be on a slick surface with less traction. Restarting while rolling backward is a good way to spin wheels and break traction. Of course, the parking brake is always available in such situations, but the Frontier and Tacoma's hillstart systems automatically apply brake pressure when the truck's on a hill to prevent backward rolling. The computer monitors throttle position, vehicle speed, and brakeline pressure to produce smooth starts in troubling situations. The system gives the driver two seconds to get moving, then releases total pressure to avoid overheating the brake-control valves.
It might seem that truckmakers are conspiring to deprive skilled enthusiast drivers of direct control of their machines through the increased use of electronics, but, in fact, electronics can help give the driver even more control. Nissan and Hummer, among others, include a different throttle map when in low range.