From Page 177-178 of my owner's manual.
Hill- start assist control system
The hill- start assist control system assists you in starting to move up a steep or slippery hill. When you start to move up the hill slope, the system helps to prevent the vehicle from rolling backward in the interval while you move your foot from the brake pedal to the accelerator pedal.

CAUTION
• Do not rely excessively on the hill- start assist control system. The vehicle may not be able to start smoothly on road surfaces or off- road surfaces such as extremely steep slopes or icy roads, on which sliding can occur very easily.
• Do not use the hill- start assist control system to stop the vehicle. This system is not designed as a function for stopping the vehicle on a uphill slope.
The hill- start assist control system will operate for 5 seconds maximally when all of the following conditions apply.
• 5- speed automatic transmission— When the transmission is in any of positions “D”, “4”, “3”, “2” or “L”
• 4- speed automatic transmission— When the transmission is in any of positions “D”, “3”, “2” or “L”
• When the brake pedal is not de- pressed
The system is designed to operate when the vehicle is starting on an uphill slope; therefore, if the transmission is in “P” or “N” it will not operate. It will not operate either if the vehicle starts to move in reverse on a slope with the transmission in the “R”.
When the hill-start assist control is operating, the slip indicator light flashes and an alarm sounds intermittently. At the same time, the stop lamps and high mounted stoplight are lit.
The slip indicator light comes on for a few seconds when the ignition key is turned to “ON”. If the indicator light does not come on when the ignition is turned on, contact your Toyota dealer.
Keep in mind the following when driving.
• The hill- start assist control system operates for 5 seconds maximally. If both the brake and accelerator pedals remain undepressed for longer than 5 seconds, the buzzer will sound at more frequent intervals and the system will gradually stop operating.
• The hill- start assist control system is not designed as a function for stopping the vehicle on a uphill slope. When stopping the vehicle, be sure to depress the brake pedal.
If the system is used frequently, the brake actuator temperature may become too high and a buzzer will sound intermittently.
In this case, a buzzer will sound intermittently. When the temperature of the brake actuator goes down, the system will begin to operate again. Until it restarts, the traction control system (two- wheel drive models), active traction control system (four- wheel drive models) and downhill assist control system will not operate; however, the conventional brake can be operated.
