Antilock Brakes / Traction Control Systems: Description and Operation

SYSTEM DESCRIPTION

System Diagram:

Function
ABS
^ Anti-Lock Brake System is a function that detects wheel revolution while braking, electronically controls braking force, and prevents wheel locking during sudden braking. It improves handling stability and maneuverability for avoiding obstacles.
^ Electrical system diagnosis by CONSULT-II is available.

EBD
^ Electronic Brake force Distribution is a following function. ABS actuator and electric unit (control unit) detects subtle slippages between the front and rear wheels during braking. Then it electronically controls the rear braking force (brake fluid pressure) to reducing and reduces rear wheel slippage. Accordingly it improves vehicle stability.
^ Electrical system diagnosis by CONSULT-II is available.

TCS
^ Traction Control System is a function that electronically controls engine torque, brake fluid pressure and A/T gear position to ensure the optimum slippage ratio at drive wheels by computing wheel speed signals from 4 wheel sensors. When ABS actuator and electric unit (control unit) detects a spin at drive wheels (rear wheels), it compares wheel speed signals from all 4 wheels. At this time, LH and RH rear brake fluid pressure are controlled, while fuel being cut to engine and throttle valve being closed to reduce engine torque by the control unit. Further more, throttle position is continuously controlled to ensure the optimum engine torque at all times.
^ During TCS operation, it informs driver of system operation by flashing SLIP indicator lamp.
^ Electrical system diagnosis by CONSULT-II is available.

VDC
^ Vehicle Dynamics Control system detects driver's steering operation amount and brake pedal travel from steering angle sensor and pressure sensor. Using information from yaw rate/side G sensor and wheel sensor, VDC judges driving condition (conditions of under steer and over steer) to improve vehicle driving stability by controlling brake application to 4 wheels and engine output.
^ During VDC operation, it informs driver of system operation by flashing SLIP indicator lamp.
^ Electrical system diagnosis by CONSULT-II is available.

ECD
Receives deceleration degree commandment value signal from ICC sensor integrated unit, and controls brake fluid pressure with the motor (built-in ABS actuator and electric unit (control unit)).

Operation That Is Not System Error
ABS
^ When starting engine or just after starting vehicle, brake pedal may vibrate or the motor operating sound may be heard from engine room. This is a normal states of the operation check.
^ During ABS operation, brake pedal lightly vibrates and a mechanical sound may be heard. This is normal.
^ Stopping distance may be longer than that of vehicles without ABS when vehicle drives on rough, gravel, or snow-covered (fresh, deep snow) roads.

TCS
^ Depending on road circumstances, driver may have a sluggish feel. This is normal, because optimum traction has highest priority under TCS operation.
^ When vehicle is passing through a road where surface friction varies, downshifting or depressing accelerator pedal fully may activate TCS temporarily.

VDC
^ During VDC operation, body and brake pedal lightly vibrate and mechanical sounds may be heard. This is normal.
^ If vehicle is rotated on turn table, or rolled and rocked on ship, ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp may turn on. In this case, start engine on normal road again. If ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp turn off after restart, it is normal.
^ When starting TCS or VDC under rapid acceleration or hard turn, operating sound by brake pedal is generated. However, this is not malfunction. This is because TCS and VDC are functioning normally.
^ VDC may not operate normally or ABS warning lamp, VDC OFF indicator lamp and SLIP indicator lamp may turn on when driving special roads with extremely steep slant (banks on circuit road and so on.) However, it is not malfunction when returning to a normal state after restarting the engine. In that case, be sure to erase the memory of self-diagnosis.
^ Yaw rate /side G sensor malfunction may occur under hard turn like spin turn, rapid acceleration turn, drift run, etc., when VDC function is OFF (VDC OFF switch is turned on). It is not malfunction if it is possible to return to a normal position after restarting engine. Then erase the memory of self-diagnosis.
^ VDC OFF indicator lamp and SLIP indicator lamp may simultaneously turn on when low tire pressure warning lamp turns on. This is not a VDC system error but results from characteristic change of tires.

Fail-Safe Function
ABS, EBD SYSTEM
In the event there is a malfunction with the electrical system, the ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp will turn on when it is the ABS that is malfunctioning, and the brake warning lamp, ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp will turn on when it is the EBD that is malfunctioning. At the same time, the VDC/TCS/ABS will be put in one of the following states by the fail-safe function.
^ When the ABS malfunctions, only the EBD operates. The condition is the same as that of models without VDC/TCS/ABS.

NOTE: In step 1 shown above, self-diagnosis is performed when ignition switch is turned ON and when vehicle initially starts. ABS self-diagnosis sound may be heard as usual.

^ When the EBD malfunctions, the EBD and ABS will not operate. The condition is the same as that of models without VDC/TCS/ABS and EBD

VDC/TCS
In case of VDC/TCS system malfunction, the VDC OFF indicator lamp and SLIP indicator lamp or only VDC OFF indicator lamp are turned on, and the condition of the vehicle is the same as the condition of vehicles without VDC/TCS equipment. In case of electrical malfunction with the VDC/TCS system, the ABS control continues to operate normally even though VDC/TCS does not operate.

CAUTION: If the Fall-Safe function is activated, then perform self-diagnosis for VDC/TCS/ABS control system.

Hydraulic Circuit Diagram:

CAN COMMUNICATION
System Description
CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only. Refer to LAN-34, CAN Communication Unit. Description and Operation