TOYOTA RAV4 2006 Service Repair Manual

BC–8BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEM
BC
(c) BA (Brake Assist):
The primary purpose of the brake assist system is to
provide auxiliary brake force to assist drivers who
cannot generate a large enough brake force during
emergency braking, thus helping to maximize the
vehicle's braking performance.
(1) Operation description:
The skid control ECU receives speed signals
from each speed sensor and the fluid pressure
signal from the master cylinder pressure sensor
to determine whether brake assist is necessary.
If brake assist is deemed necessary, the skid
control ECU sends control signals to the pump
motor and solenoid. The pump and the solenoid
valve then control the pressure applied to each
wheel cylinder. The ABS warning light comes on
to indicate malfunctions in the BA (brake assist)
system.
w/ 16-inch disc: The brake warning light and
ABS warning light come on to indicate
malfunctions in the BA system.
C135908E01

BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEMBC–9
BC
(d) TRC (Traction Control):
The TRC system helps prevent the drive wheels
from slipping if the driver presses down on the
accelerator pedal excessively when starting off or
accelerating on a slippery surface.
C115102E02

BC–10BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEM
BC
(1) Operation description:
The skid control ECU detects the vehicle's slip
condition by receiving signals from each speed
sensor and the ECM via CAN communication.
The skid control ECU controls engine torque
with the ECM via CAN communication and
brake fluid pressure through the pump and
solenoid valve. The slip indicator light blinks
when the system is operating.
for 4WD: The VSC warning light comes on when
the TRC system malfunctions.
for 2WD: The VSC warning light and SLIP
indicator light comes on when the TRC system
malfunctions.

BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEMBC–11
BC
(e) VSC (Vehicle Stability Control):
The VSC system helps prevent the vehicle from
slipping sideways when front or rear wheel skidding
occurs while cornering.
C115103E02

BC–12BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEM
BC
(1) Operation description:
The skid control ECU determines the vehicle
condition by receiving signals from the speed
sensor, the yaw rate and deceleration sensor
and the steering sensor. The skid control ECU
controls engine torque with the ECM via CAN
communication and brake fluid pressure through
the pump and solenoid valve. The slip indicator
light blinks and the skid control buzzer sounds
when the system is operating.
for 4WD: The VSC warning light comes on when
the TRC system malfunctions.
for 2WD: The VSC warning light and slip
indicator light come on when the TRC system
malfunctions.
(f) Downhill Assist Control:
When the downhill assist control switch is pressed
with the shift lever on L or R range and the
accelerator and brake pedals not depressed,
downhill assist control is activated. When activated,
4-wheel hydraulic pressure control occurs in order
to maintain a constant low vehicle speed without
causing the wheels to become locked. Thus, the
vehicle can descend a steep hill in a stable manner.
HINT:
• Depressing the accelerator and brake pedal
cancels control of the downhill assist control.
• Downhill assist control begins operating when
driving down on a slope at a speed of 25 km/h
(16 mph) or less with the engine brake applied.

BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEMBC–13
BC
(1) Operation description:
The slip indicator light blinks and the downhill
assist control indicator light and brake light come
on when the system is in operation.
The VSC warning light comes on and the
downhill assist control indicator light blinks to
indicate a malfunction in the downhill assist
control.
C136089E01

BC–14BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEM
BC
(g) Hill-start assist control:
When the vehicle starts off on a steep hill, hill-start
assist control effects 4-wheel hydraulic pressure
control to prevent the vehicle from rolling
backwards.
After a maximum of 2 seconds after the control has
started, fluid pressure is gradually released and
control will be complete.
HINT:
• Depressing the brake pedal cancels control of
the hill-start assist control.
• Hill-start assist control does not operate when
the shift lever is in the P position, or when the
vehicle is running, the parking brake lever is set,
or the accelerator pedal is depressed.
C132095E01

BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEMBC–15
BC
(1) Operation description:
When the system is in operation, the following
occurs: 1) the slip indicator light blinks; 2) the
VSC light comes on; and 3) when hill-start assist
control operation starts, the skid control buzzer
sounds once; when hill-start assist control
operation ends, the skid control buzzer sounds
twice.
The VSC warning light comes on when the hill-
start assist control is malfunctioning.
(h) AUTO LSD (Auto Limited Slip Differential) for 2WD:
The AUTO LSD achieves the equivalent functions of
an LSD (Limited Slip Differential) through the use of
a traction control system. When the driver presses
the AUTO LSD switch, this system achieves the
LSD effect by regulating the hydraulic pressure that
acts on the drive wheels and controlling the engine
output in accordance with the amount of pedal effort
applied on the accelerator. The AUTO LSD
operates with the AUTO LSD switch on and the
accelerator pedal depressed.
Auto LSD restrains brake pressure and reduces
differential movement, thus transmitting the drive
torque to the other drive wheel to ensure stability
under the following conditions:
• Wheels run off the road.
• Drive wheels spin in place when starting on a
slope with one wheel on snow/ice.
HINT:
Releasing the accelerator pedal cancels control of
the AUTO LSD system.

BC–16BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEM
BC
C136090E01

BRAKE CONTROL – VEHICLE STABILITY CONTROL SYSTEMBC–17
BC
(1) Operation description:
The skid control ECU determines that the
vehicle is in a state in which the AUTO LSD can
operate by using various sensors and switches
to detect the operating conditions of the AUTO
LSD switch, shift position, accelerator pedal, and
brake pedal. When the vehicle is in a state in
which the AUTO LSD can operate, the skid
control ECU effects hydraulic pressure control of
the wheel cylinder at the wheel with the faster
wheel speed so that the wheel speeds of the
right and left drive wheels will become equal.
The slip indicator light blinks and the AUTO LSD
indicator light comes on when the system is
operating. Both the VSC warning light and SLIP
indicator light come on when the AUTO LSD
system malfunctions.
2. COOPERATIVE CONTROL FUNCTION
(a) Description
(1) Braking when Surface Resistance Differs
Between Left and Right Wheels
If the driver suddenly applies the brakes on a
road surface with a considerable difference in
friction coefficient between the right and left
wheels, the difference in the brake force
between the right and left wheels will cause the
vehicle posture to become unstable and create a
yaw movement. In this state, the skid control
ECU controls the VSC to stabilize the vehicle
posture. At the same time, it effects cooperative
control with the EPS to provide steering torque
assist, which facilitates the driver's steering
maneuvers to stabilize the vehicle posture.
(2) Accelerating when Surface Resistance Differs
Between Left and Right Wheels
If the driver suddenly starts off or accelerates on
a road surface with a considerable difference in
friction coefficient between the right and left
wheels, the slippage of a drive wheel will cause
the vehicle posture to become unstable and
negatively affect its acceleration performance. In
this state, the skid control ECU causes the TRC
to control the hydraulic brake of the slipping
drive wheel, and requests the engine ECU to
effect engine output control. At the same time, it
effects cooperative control with the EPS to
provide steering torque assist, which facilitates
the driver's steering maneuvers to stabilize the
vehicle posture.