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.
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, in that case a fault is detected by detecting abnormal input current. HECU cut off the voltage supply to wheel sensor channel which had a fault and prevent vehicle’s damage due to super heated harness.
If one or more defects has detected, DTC code of defected wheel will be stored. Mutual short between sensors is detected by executing self diagnosis successively at corresponding wheel when ignition ON.
Warning lamp is turned OFF unless fault is detected any more when the IG KEY is turned ON again.
Item | Detecting Condition | Possible cause | |
DTC Strategy | ● Voltage monitoring | ● Open or short of Wheel speed sensor circuit(RR) ● Faulty Wheel speed sensor(RR) | |
Case1 | Monitoring Period | ● Once after power up. | |
Enable Conditions | ● Shorts between WSS lines and shorts to UZ can be detected by switching single WSS channels in sequence. If there is an error after end of test, a failure is recognized. Remark: In case of a WSS power line short to V_batt, this FSA test will detect an under voltage failure. (ABS only) ※ FSA test : fail save circuit test ※ UZ : Ignition Voltage | ||
Case2 | Monitoring Period | ● Continuous | |
Enable Conditions | ● When the sensor current levels are out of permissible range(LOW : 7mA, HIGH : 14mA) for 200ms. | ||
Fail Safe | ● Sensor failure outside of the ABS control cycle 1. 1~2 wheel failure - Only the ABS/ESP functions are inhibited. . - The ABS/ESP warning lamps are activated and the EBD warning lamp is not activated. 2. More than 3 wheels failure - The ABS/EBD/ESP functions are inhibited. - The ABS/EBD/ESP warning lamps are activated. ● Sensor failure inside the ABS control cycle 1. 1~2 wheel failure - Inhibit the ABS/ESP control. - The ABS/ESP warning lamps are activated and the EBD warning lamp is not activated. 2. More than 3 wheels failure - The ABS/EBD/ESP functions are inhibited. - The ABS/EBD/ESP warning lamps are activated. ※ Control of the corresponding wheel is no longer possible. If a sensor fault occurs on a front wheel, pressure is increased; on a rear wheel, pressure is decreased. | ||
Sensor Type | Output Voltage | Airgab | |
HIGH | LOW | ||
Active Type | 1.05V | 0.525V | 0.5mm |
