ABS/TCS

Description

PURPOSE
The Anti-lock Brake System (ABS) consists of electronic and hydraulic components. It allows for control of braking force so that locking of the wheels can be avoided.
The ABS:
- Ensures proper tracking performance through steering wheel operation.
- Enables obstacles to be avoided through steering wheel operation.
- Ensures vehicle stability by preventing flat spins.

ABS (ANTILOCK BRAKE SYSTEM) OPERATION
- When the vehicle speed is less than 10 km/h (6 MPH) this system does not work.
- The ABS has self-test capabilities. The system turns on the ABS warning lamp for 1 second after turning the ignition switch ON. The system performs another test the first time the vehicle reaches 6 km/h (4 MPH). A mechanical noise may be heard as the ABS performs a self-test. This is a normal part of the self-test feature. If a malfunction is found during this check, the ABS warning lamp will come on.
- During ABS operation, a mechanical noise may be heard. This is a normal condition.

TCS (TRACTION CONTROL SYSTEM) OPERATION
- This system is designed to limit wheel slip during acceleration by changing the transmission shift schedule (with A/T) and cutting fuel to selected engine cylinders.
The ABS actuator and electric unit (control unit) detects drive wheel slip by comparing wheel speed signals from all 4 wheels. The ABS actuator and electric unit (control unit) will then determine the desired torque reduction needed to minimize wheel spin.
The torque reduction by the ABS actuator and electric unit (control unit) may result in a combination of transmission shift timing adjustments (with A/T) and fuel cutoff.
The torque reduction is sent from the ABS actuator and electric unit (control unit) through the CAN (Controller Area Network) lines to the TCM (with A/T) and the ECM. The ECM will cut fuel and/or the TCM will change transmission shift schedule to achieve torque reduction.
The TCS will be enabled when the TCS ON/OFF switch is in the ON position (TCS OFF indicator not illuminated), and if the catalytic converter temperature is within the normal operating range.
- During TCS operation, the system informs the driver of system operation by flashing the SLIP indicator lamp.
- This system has a self-diagnostic function. When the ignition switch is initially turned ON, the SLIP indicator lamp and TCS OFF indicator lamp will illuminate. If the ABS/TCS system is operating correctly, both indicator lamps will go out as soon as the engine starts.
- The TCS ON/OFF switch cancels the TCS function. The TCS OFF indicator lamp then illuminates to indicate that the TCS system is not operating.
This system utilizes a fuel-cut function to control drive torque. If fuel-cut continues for an extended period of time during high-speed operation, the catalyst may melt and deteriorate. During continued TCS operation, the system will sometimes suspend the drive torque control function, preventing catalyst damage.

Fail Safe
If trouble occurs in the ABS, the ABS warning lamp in the combination meter will turn on. At the same time, the ABS actuator and electric unit (control unit) will disable ABS control, and braking becomes the same as that of a vehicle without ABS.





Hydraulic Circuit





System Components

Control Unit
ABS FUNCTION





The control unit computes the wheel rotating speed by the signal sent from the sensor. Then it supplies a DC current to the actuator solenoid valve. It also controls ON-OFF operation of the valve relay and motor relay. If any electrical malfunction should be detected in the system, the warning lamp is turned on. In this condition, the ABS will be disabled, and the vehicle's brake system reverts to normal operation.

TCS FUNCTION





Drive wheel slippage is determined by comparing speed signals from all 4 wheels. When the wheel slip becomes excessive, the TCS operates, causing the SLIP indicator lamp to flash. At the same time, a signal requesting a change in the shift schedule will be sent to the TCM (with A/T) and a fuel-cut signal is sent to the ECM. When the TCS ON/OFF switch is used to cancel TCS function, the TCS OFF indicator lamp will light. (TCS does not activate.) In case of a malfunction in the TCS, both the SLIP indicator lamp and the TCS OFF indicator lamp will light, while shutting down the TCS system operation. The vehicle will operate in the same way as a vehicle not equipped with TCS.

ABS Actuator and Electric Unit
The ABS actuator and electric unit (control unit) contains:
- An electric motor and pump
- Two relays
- Eight solenoid valves, each inlet and outlet for
LH front
RH front
LH rear
RH rear
- ABS control unit
These components control the hydraulic circuit. The ABS actuator and electric unit (control unit) directs the actuator to increase, hold or decrease hydraulic pressure to all or individual wheels. The ABS actuator and electric unit (control unit) cannot be disassembled and must be replaced as an assembly.





ABS ACTUATOR OPERATION

Wheel Sensors





The front wheel sensor units consist of a gear-shaped sensor rotor and a sensor element. The element contains a magnet around which a coil is wound. The front wheel sensors are installed on the front of the wheel knuckles. As the wheel rotates, the sensor generates a square-wave signal. The frequency increases as the wheel speed Increases.





The rear wheel sensor units consist of wheel hubs with a series of internal magnets and a sensor element. The rear wheel sensors are installed on the inner side of the wheel knuckles. As the wheel rotates, the sensor generates a square-wave signal. The frequency increases as the wheel speed increases.

CAN Communication System Description
Refer to "CAN COMMUNICATION".