Anti-Lock - Traction Control: Description
Anti-Lock Brake System (ABS) consists of a hydraulic unit with 4 solenoid switching valves, 4 pulse (speed) sensors, an Electronic Control Unit (ECU), relays and wiring harness. See Fig 1 .
An ANTI-LOCK indicator light, located on instrument panel, lights up when ignition is turned on. This indicator light goes out once engine is started, indicating ABS is ready for operation.
ABS activates at speeds greater than 8 MPH. When vehicle speed is greater than 3 MPH, the built-in electronic test monitor will start checking ABS. If fault is found, warning light will come on. When ABS light is on, ABS is switched off. Vehicle will then convert to conventional braking.
If battery voltage is less than 10.5 volts with ignition on and test speed is exceeded, ABS will remain off until alternator increases voltage output to more than 10.5 volts. ABS warning light will then go out.
Traction control system, called Automatic Stability Control (ASC), controls slip of drive wheels regardless of road surface conditions. During a control phase, engine torque is reduced by Digital Motor Electronics (DME) system and throttle control system (EML). Additionally, the EGS control unit modifies gear shift points in response to a signal from the ASC+T control unit. If this is not sufficient, drive wheel which is spinning too fast is braked using wheel brake in conjunction with a hydraulic actuator. When wheel spin is detected, the control circuits can intervene. If at least one wheel exhibits a speed difference of 1.8 mph, the ASC+T system intervenes.
For this reason, the condition of all four tires must be uniform. Deviating pressures or tire diameters may activate the system unnecessarily. The system must be switched off if snow chains or snow tires are installed. It should also be switched off when crossing a surface of loose gravel , etc.
ASC light in instrument cluster comes on constantly when ignition is switched on as a bulb check. System is switched on after engine start and can be switched off as necessary. ASC light is off when system is switched on. If ASC light is flashing, ASC control is active. If ASC light remains on, system has switched off automatically because of a fault or was switched off manually.