Hill Descent Control (HDC) (page 3 of 3)

BRAKES

70-30

DESCRIPTION AND OPERATION

Hill Descent Control Enable Criteria

 The target speed used by the HDC varies in response to driver inputs. Current target speed will lie in the range 
between Maximum Target Speed and Minimum Target Speed.

Hill Descent Control Target Speeds

When HDC is first activated, if the driver does not press the brake or accelerator pedals, then current target speed is 
set to default target speed. If HDC is activated and the driver presses the brake pedal, the vehicle brakes operate as 
normal. While the brake pedal is pressed:

l

If vehicle speed is equal to or more than current target speed, current target speed is unchanged

l

If vehicle speed is less than current target speed, current target speed is set to vehicle speed

When the brake pedal is released:

l

If vehicle speed is equal to or more than minimum target speed, then current target speed is unchanged

l

If vehicle speed is less than minimum target speed, then Current Target Speed is set to minimum target speed.

If HDC is activated and the driver presses the accelerator pedal, current target speed is defined by a characteristic as 
follows:

l

If current target speed is less then default target speed, then the target speed is set to current speed.

When the accelerator pedal is released:

l

If current target speed is greater than default target speed and vehicle speed is equal to or more than default 
target speed, then current target speed is set to default target speed

l

 If current target speed is more than default target speed and vehicle speed is less than default target speed, 
then current target speed is set to vehicle speed

l

 If current target speed is less than or equal to default target speed, and vehicle speed is less than current target 
speed , then current target speed is set to vehicle speed

l

 If current target speed is less than or equal to default target speed , and vehicle speed is equal to or more than 
current target speed , then current target speed is unchanged.

To ensure that the vehicle is in an appropriate gear during HDC activity the ABS ECU communicates with the EAT 
ECU. A unique gearbox map is activated when HDC braking activity begins. The characteristics of the map are that 
lower gears are selected sooner than normal, and higher gears are selected later than normal. This reduces the work 
done by the foundation brakes, and improves the response time of HDC.

 Gear Detected

 Neutral

 Auto Transmission D, 1-5, R 

Throttle less than 5%

 Enabled

 Enabled

 5% to 20%

Stand by

 Enabled

Throttle more than 
20%

Stand by

Stand by

 Low

High

Gear 
selector  
position

D

1

2

3

4

5

R

N

 

D,1,2,3,

4,5

R

N

Maximum 
target 
speed

35 km/h

(22 mph)

35 km/h

(22 mph)

35 km/h

(22 mph)

35 km/h

(22 mph)

35 km/h

(22 mph)

35 km/h

(22 mph)

35 km/h

(22 mph)

—

35 km/h

(22 mph)

35 km/h

(22 mph)

—

Standard 
target 
speed

6 km/h

(4 mph)

3.5 km/h

(2 mph)

6 km/h

(4 mph)

6 km/h

(4 mph)

6 km/h

(4 mph)

6 km/h

(4 mph)

3.5 km/h

(2 mph)

6 km/h

(4 mph)

10 km/h

(6 mph)

6 km/h

(4 mph)

10 km/h 

(6 mph)

Minimum 
target 
speed

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

3.5 km/h

(2 mph)

 6 

km/h

(4 mph)

6 km/h

(4 mph)

6 km/h 

(4 mph)