Toyota 2012 Highlander Owner's Manual page 208

2-4. Using other driving systems
Downhill assist control system (4WD models)
With the downhill assist control system, the vehicle is able to
descend a steep hill, maintaining a constant low speed of about 3
mph (5 km/h) without brake pedal operation.
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Activating the downhill assist control system
While the downhill assist control system is operating
230
Press the "DAC" switch.
The downhill assist control sys-
tem indicator will come on to
indicate that the downhill assist
control system is activated.
Pressing the switch again turns
the system off.
The slip indicator will flash to
indicate that the downhill assist
control system is operating, and
the stop lights and high mounted
stoplight will turn on.