The wheel speed sensor is the essential component the ABS ECU uses to calculate vehicle speed and to determine whether wheel lock occurs. For example, rear wheel speed signal is used as a referecnce value, for vehicle speed, in front wheel drive vehicles, and if a difference between front and rear wheel speed occurs, then ABS control is performed. Wheel speed sensor is active hall-sensor type and good at temperature and noise chariteristic. Digital wave is produced as tone wheel rotate according as hall sensor principle. Frequency of duty wave is changed in proportion to rotation of tone wheel and HECU calculate vehicle speed by this frequency.
The ABS ECU monitors the wheel speed sensor circuit continuously. A direct current is supplied in the wheel-speed sensor by a power source in the input amplifier of the control unit. If the WSS circuit is broken, the input of the amplifier recognizes a potential shift caused by the supplied current and a fault is detected. HECU cut off the supply voltage for wheel sensor channel which had a fault and prevent vehicle’s damage due to super heated harness. Warning lamp is turned OFF if the detected fault is not more than when the IG KEY is turned to ON again
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Resistance monitoring | ● Open or short Wheel speed sensor(RR) ● Faulty Wheel speed sensor(RR) ● Faulty HECU |
Monitoring Period | ● Continuously | |
Enable Conditions | ● A direct current is injected in the wheel-speed sensor by a power source in the input amplifier of the control unit. If the WSS circuit is broken, the input of the amplifier recognizes a potential shift caused by the injected current and a fault is detected. HECU cut off the supply voltage for wheel sensor channel which had a fault and prevent vehicle’s damage due to super heated harness. Starts with a filter time of 200ms after initialization. | |
Fail Safe | ● Sensor failure outside the ABS control cycle ABS is switched off immediately. ● Sensor failure inside the ABS control cycle 1. If only one wheel is in ABS control and a sensor fault is detected at this wheel,then : ABS is switched off immediately. 2. If several wheels are in ABS control, then :ABS is switched off at the end of ABS control. ● If a sensor fault occurs on a front wheel, pressure is increased; on a rear wheel, pressure is decreased. (until switch off). ● ABS control of the corresponding wheel is no longer possible ● The ABS warning lamp is activated and the EBD warning lamp is not activated. |
