Antilock Brakes / Traction Control Systems: Description and Operation

Purpose
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:
1. Ensures proper tracking performance through steering wheel operation.
2. Enables obstacles to be avoided through steering wheel operation.
3. 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.





ABS HYDRAULIC CIRCUIT

TCS (Traction Control System) Operation
- This system is designed to limit wheel slip during acceleration by cutting fuel to selected cylinders and changing transmission shift schedule.
The ABS/TCS control unit monitors wheel speed slips through the ABS wheel sensors and determines the desired torque reduction needed to minimize wheel spin.
The torque reduction by the ABS/TCS control unit may result in a combination of fuel cutoff and change shift timing of the transmission.
The torque reduction is sent from the ABS/TCS control unit through the data link to the ECM and TCM. The ECM will cut off fuel and/or TCM change 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 normal operating range.
- This system has a self-diagnostic function. When the ignition switch is initially turned "ON", the SLIP indicator lamp and TCS OFF indicator lamp light. If there is no problem with the ABS and TCS, 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 lights to indicate that the TCS 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 operations, the catalyst may melt and deteriorate. During continued TCS operations, the system will sometimes suspend the drive torque control function, preventing catalyst melting and deterioration.



CONTROL UNIT
ABS Function





The control unit computes the wheel rotating speed by the signal current 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. And, 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 the TCS.