2003 LEXUS LS430 brake sensor

When there is a malfunction in the contact point of the terminals or installation problems with parts,
removal and installation of the suspected problem parts may return the system to the normal condition
either completely or temporarily.
In order to determine the malfunctioning area, be sure to check the conditions at the time the malfunction
occurred, such as by DTC output and the freeze frame data output, and record it before disconnecting
each connector or removing and installing parts.
Since the ABS with EBD & BA & TRAC & VSC systems may be influenced by a malfunction in the
other systems, be sure to check for DTCs in the other systems.
Be sure to remove and install the skid control ECU, ABS & TRAC actuator and each sensor with the IG
switch OFF unless specified in the inspection procedure.
When removing and installing the skid control ECU, ABS & TRAC actuator and each sensor, be sure to
check that the normal display is output in test mode inspection and in DTC output inspection after
installing all the parts.
After replacing the yaw rate sensor and/or the brake actuator assembly, make sure to perform yaw rate
sensor and deceleration sensor zero point calibration.
(see CALIBRATION
)
CAN communication system is used for the data communication between the skid control ECU (included
in the actuator), the steering angle sensor, and the yaw rate sensor (the deceleration sensor is included). If
there is trouble in the CAN communication line, the DTC in the communication line is output.
If the DTC in the CAN communication line is output, repair the malfunction in the communication line
and troubleshoot the ABS with EBD & BA & TRAC & VSC systems under the condition that data
communication is normal.
Since the CAN communication line has its own length and route, it can not be repaired temporarily with
the bypass wire, etc.
SYSTEM NAME REFERENCE
System NameSee Procedure
Front Power Seat Control SystemINITIALIZATION

1.SYSTEM DESCRIPTION
HINT:
The skid control ECU is a single unit with ABS & TRACTION ACTUATOR.
The skid control ECU also works as a TPMS (Tire Pressure Monitor System) ECU.
The yaw rate sensor and deceleration sensor are combined and in a single unit. This unit
communicates with the skid control ECU through CAN communication.
a. ABS (Anti-lock Brake System)
The ABS helps prevent the wheels from locking when the brakes are applied firmly or when
braking on a slippery surface.
ECUSystem
ECMSkid Control ECUShift Position SignalCAN Communication
System
ECMSkid Control ECUThrottle Position SignalCAN Communication
System
ECMSkid Control ECUEngine Revolution SignalCAN Communication
System
ECMSkid Control ECUWater Temperature Sensor
SignalCAN Communication
System
ECMSkid Control ECUIntake Air Temperature Sensor
SignalCAN Communication
System
Skid Control ECUECMYaw Rate (Deceleration) SignalCAN Communication
System
Skid Control ECUECMVSC Data SignalCAN Communication
System
Skid Control ECUGate Way ECUBrake Warning Lamp ON
SignalBEAN System
Skid Control ECUGate Way ECUABS Warning Lamp ON SignalBEAN System
Skid Control ECUGate Way ECUTRAC OFF Indicator ON
SignalBEAN System
Skid Control ECUGate Way ECUSlip Indicator ON SignalBEAN System
Skid Control ECUGate Way ECUMulti Information display
SignalBEAN System

Fig. 5: ABS & TRACTION Actuator - Electronic Brake Force Distribution
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
Operation description
The skid control ECU receives the speed signal from each speed sensor to detect the slip condition
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The solenoid valve controls the oil pressure of each wheel cylinder and splits the control power
properly between the front and rear wheels and the right and rear wheels.
Both of the ABS warning lamp and the brake warning lamp come on to indicate a malfunction in
the EBD system.
c. BA (Brake Assist)
The primary purpose of the brake assist system is to provide an auxiliary brake force to assist the
driver who cannot generate a large enough brake force during emergency braking, thus helping to
maximize the vehicle's brake performance.

Fig. 6: ABS & TRACTION Actuator - Brake Assist
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
Operation description
The skid control ECU receives the signal from the stop lamp switch and the oil pressure signal
from the master cylinder pressure sensor to determine whether brake assist is necessary or not. If
brake assist is deemed necessary, the 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 lamp comes on to indicate a malfunction in the brake assist system.
d. TRAC (Traction Control)
The TRAC system helps prevent the drive wheels from slipping if the driver presses down on the
accelerator pedal excessivel
y when starting off or accelerating on a slippery surface.

Fig. 8: ABS & TRACTION Actuator - Vehicle Stability Control
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
Operation description
The skid control ECU determines vehicle condition by receiving signals from the speed sensor, yaw rate
and deceleration sensor and steering angle sensor. The skid control ECU controls engine torque with the
ECM, vehicle position with suspension control ECU via CAN communication, and oil pressure with the
pump and solenoid valve. The warning light comes on and the buzzer sounds when the system is
operating.
2.ABS with EBD & BA & TRAC & VSC OPERATION
a. Skid control ECU calculates vehicle stability tendency based on the signal of sensors, speed sensor,
yaw rate and deceleration sensor and steering angle sensor. And it judges whether the control of
engine output torque by electronic control throttle and of wheel brake pressure by brake actuator
will operate or not by the calculation results.
b. The SLIP indicator blinks and the VSC buzzer sounds to inform the driver that the VSC system is
operating. The SLIP indicator also blinks when TRAC is operating, and the operation being
performed is displayed.
3.FAIL SAFE FUNCTION
a. When a failure occurs in the ABS with BA & TRAC & VSC systems, the ABS warning light and
the VSC warning light turns on and the ABS with BA & TRAC & VSC operations are prohibited.
In addition to this, when there is a failure that disables the EBD operation, the brake warning light
also comes on and the EBD operation is prohibited (see FAIL
-SAFE CHART ).
b. If some control is prohibited due to a malfunction during it's operation, that control will be cut off
gradually not to change stability of vehicle suddenly.
4.PRE-COLLISION BRAKE ASSIST SYSTEM (w/ PRE-COLLISION BRAKE ASSIST SYSTEM)

Fig. 19: Identifying VSC Location
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
If the indicator remains on, proceed to troubleshooting for the light circuit below.
TROUBLE AREA REFERENCE
2.SENSOR SIGNAL CHECK BY TEST MODE
HINT:
If the ignition switch is turned from ON to the ACC or LOCK position during test mode, DTC of
Trouble areaSee Procedure
ABS warning light circuitABS WARNING LIGHT CIRCUIT (REMAINS ON)
BRAKE warning light circuitBRAKE WARNING LIGHT CIRCUIT
TRAC OFF indicator light
circuitTRAC OFF INDICATOR LIGHT, TRAC OFF SWITCH
CIRCUIT
SLIP indicator light circuitSLIP INDICATOR LIGHT CIRCUIT

HINT:
The blinking pattern of the ABS warning lamp and the "VSC Test" display on the multi-
information do not change. When the sensor is normal and in the test mode, if the above conditions
are met, the check is completed.
Fig. 22: Identifying VSC Test Location

Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
c. CHECK THE MASTER CYLINDER PRESSURE SENSOR
1. Leaving the vehicle in a stationary condition engine is off and the brake pedal in a free
condition for 1 second. or more, continue to quickly depress the brake pedal with a force of
98 N (10 kgf, 22 lbf) or more for 1 second, or more.
HINT:
At this time, the ABS warnin
g light stays on for 3 seconds.

Fig. 24: Identifying VSC Test Location
Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
e. BRAKE PEDAL LOAD SENSING SWITCH CHECK
1. Keep depressing the brake pedal for one second or more with a brake pedal load of
approximately 59 N (6kgf) with the ignition switch in the ON position (engine is off).
2. Check if the brake warning lamp comes on and the ABS motor operating sound can be heard.
HINT:
If rechecking the brake pedal load sensing switch after the engine starts, exit the test mode
and enter the test mode to release the negative pressure in the booster by pumping the brake
pedal.
3. Start the engine and depress the brake pedal with a brake pedal load of approximately 59 N
(6 kgf) or more to check if the brake warning lamp goes off.
f. SPEED SENSOR CHECK
1. Check the ABS warnin
g lamp is blinking in TEST MODE.