People who love exploring back woods trails that require the engagement of a low-range four-wheel-drive system probably know what it feels like to be stuck or stopped on a steep hillside, unsure how to ascend or descend safely and securely. Toyota’s Hill-start Assist Control (HAC) and Downhill Assist Control (DAC) aim to give drivers a safety net in these conditions. Offered on the Lexus GX 470 and Toyota 4Runner SUVs since 2003, HAC and DAC are also available on the redesigned 2005 Toyota Tacoma pickup.
Using active wheel speed sensors and the braking system, HAC helps to prevent a vehicle from rolling backward or sliding sideways during the brief period when the driver releases the brake pedal and depresses the accelerator pedal. However, HAC is not a “hill-holder” mechanism – Toyota says it works for about three seconds, enough time to take your foot off the brake, place it onto the gas, and get the vehicle moving up the hillside. Only vehicles equipped with an automatic transmission can be equipped with HAC.
Using a brand-new 4Runner, we tried the system out on a 20-percent grade with the four-wheel-drive system in 4Lo. We sat, and sat, and sat – for at least half a minute – without a foot on the brake or on the gas. The 4Runner didn’t budge. So we had to take Toyota’s word for HAC’s three-second timeout limit, because all we learned is that a 4Runner’s V6 produces enough torque to hold the truck still on a paved 20-percent grade when the transfer case is in 4Lo.
DAC, on the other hand, is a handy piece of technology. Using a combination of engine braking and 4Lo gearing to hold a vehicle between two and four miles per hour for steep descents, DAC ensures steady, careful progress in dicey conditions. DAC will work with both manual and automatic transmissions, but requires 4WD and use of the transfer case’s 4Lo setting. Just don’t tap the brakes or the accelerator, because DAC demands your trust to work properly. If you get nervous and override the system with the pedals, you’re on your own.
