ABS/TCS
DescriptionPURPOSE
The 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 (ANTI-LOCK BRAKE SYSTEM) OPERATION
- When the vehicle speed is less than 10 km/h (6 MPH) this system does not work.
- The Anti-Lock Brake System (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 cutting fuel to selected engine cylinders and changing the transmission shift schedule.
The ABS actuator and electric unit (control unit) monitors wheel speed slips through the ABS wheel speed sensors and determines 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 fuel cutoff and transmission shift timing adjustments.
The torque reduction is sent from the ABS actuator and electric unit (control unit) through the CAN (Controller Area Network) to the ECM and the TCM. 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 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 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 meter comes on. At the same time, the vehicle stops the 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 deactivated, and the vehicle's brake system reverts to normal operation.
TCS FUNCTION
Drive wheel slippage is detected by the 4-wheel rotating speed signal. When the wheel slip becomes excessive, the TCS operates, causing the SLIP indicator lamp to flash. At the same time, a fuel-cut signal to be sent to the ECM and a signal requiring a change in the shift schedule is sent to the TCM. When the TCS 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 control unit (control unit) cannot be disassembled and must be replaced as an assembly.
ABS ACTUATOR OPERATION
Wheel Sensors
The front 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 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.
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.
FOR TCS MODELS
System diagram
Input/output signal chart
FOR A/T MODELS
System diagram
Input/output signal chart
FOR M/T MODELS
System diagram
Input/output signal chart