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. The wheel speed sensor generates sinewave signals, based on magnetic field made by a permanent magnet in the speed sensor, when the tone wheel rotates. The frequency and AC voltage changes in proportion to the wheel speed, and the HECU determines the speed by calculating the frequeny of the signal.
The ABS ECU monitors the wheel speed sensor circuit continuously. The monitoring method for this sensor is to check the (-) side signal of the sensor circuit when a reference voltage is applied to (+) side of the sensor circuit. If the (-) side voltage is out of normal range ( 2.15 ~ 3.5 V ) for more than 140 ms when the vehicle is operating below 7 Km/h, then the HECU determines that the circuit is open/short, and sets this code. Warning lamp is turned OFF if the detected fault is not more than when the IG KEY is turned to ON again, and wheel speeds are more than 10 Km/h.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Voltage monitoring | ● Open or short Wheel speed sensor circuit(FR) ● Faulty Wheel speed sensor(FR) ● Faulty HECU |
Detect Mode | ● Initial Check ● Outside the ABS control cycle ● Inside the ABS control cycle ● Diagnosis mode ● Failure mode | |
Enable Conditions | ● When the offset voltage of the sensor is outside the 2V±10% ~ 4V±10% for 140msec, the failure is detected. | |
Fail Safe | ● Sensor failure outside of the ABS control cycle 1. Only one wheel failure : Only the ABS/TCS functions are inhibited. The ABS/TCS warning lamps are activated and the EBD warning lamp is not activated. 2. More than two wheels failure : System down. The ABS/EBD/TCS functions are inhibited. The valve relay and all solenoids are prevented from being switched on. The ABS/EBD/TCS warning lamps are activated. ● Sensor failure inside the ABS control cycle 1. One front wheel failure : Inhibit the ABS/TCS control of the failed-wheel and maintain the ABS/TCS control of normal wheel. After the ABS/TCS control, the ABS/TCS functions are inhibited. The ABS/TCS warning lamps are activated and the EBD warning lamp is not activated. 2. Failure at one rear wheel : ABS/TCS control of both front wheels are inhibited and the pressure of both rear wheels are decreased. After the controller completes the ABS/TCS control, the ABS/TCS functions are inhibited. The ABS/TCS warning lamps are activated and the EBD warning lamp is not activated. 3. More than 2 wheels failure : System down. The ABS/EBD/TCS functions are inhibited. The valve relay and all solenoids are prevented from being switched on. The ABS/EBD/TCS warning lamps are activated. |
