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 signal continuously. This code is set if an abnormal speed change ratio is detected while the vehicle speed is more than 2Km/h . 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 | ● Signal monitoring | ● Improper installation of wheel speed sensor ● Abnormal Rotor and wheel bearing ● Faulty Wheel speed sensor(RL) ● Faulty HECU |
Detect Mode | ● Outside the ABS control cycle ● Inside the ABS control cycle ● Diagnosis mode ● Failure mode | |
Enable Conditions | Case1(Wrong Exciter) | ● Max. wheel velocity exceeds 20km/h and the wheel velocity is 40% of max. wheel velocity. if this condition is lasted for 2 minutes. ● Max. wheel velocity exceeds 40km/h and the wheel velocity is 60% of max. wheel velocity. if this condition is lasted for 2 minutes. |
Case2 (Speed Jump) | ● Controller counts the number of the wheel acceleration of 100g[(25km/h) for 7ms]. When the numbers at one wheel exceed 56 times, or When the numbers at more two wheels exceed 5 times, controller recognize the failure. ● Controller counts the number of the wheel acceleration of 70g[(17.5km/h) for 7ms]. When the numbers at one wheel exceed 126 times, or When the numbers at more two wheels exceed 20 times, controller recognize the failure. ● Controller counts the number of the wheel deceleration of -100g[(-25km/h) for 7ms]. When the numbers at each wheel exceed 56 times, controller recognize the failure. ● The wheel deceleration of ?100g[(-25km/h) for 7ms] causes the controller to start monitoring this failure and to compare the wheel velocity with the vehicle velocity from next cycle. When its difference of -100g is continued for more than 140msec, controller recognize the failure. ● In case that any sensor failure at other wheel was already detected, When the numbers of 100g at each wheel exceed 5 times, or When the numbers of 70g at each wheel exceed 20 times, controller recognize the failure. - The counter of speed jump is cleared every 30min. - This monitoring is performed for the period that the velocity of each wheel exceeds 2km/h. | |
Fail Safe | ● Sensor failure outside of the ABS control cycle 1. Only one wheel failure : Only the ABS/TCS/ESP functions are inhibited. The ABS/TCS/ESP warning lamps are activated and the EBD warning lamp is not activated 2. More than two wheels failure : System down. The ABS/EBD/TCS/ESP functions are inhibited. The valve relay and all solenoids are prevented from being switched on. The ABS/EBD/TCS/ESP warning lamps are activated. ● Sensor failure inside the ABS control cycle 1. One front wheel failure : Inhibit the ABS/TCS/ESP control of the failed-wheel and maintain the ABS/TCS/ESP control of normal wheel. After the ABS/TCS/ESP control, the ABS/TCS/ESP functions are inhibited. The ABS/TCS/ESP warning lamps are activated and the EBD warning lamp is not activated. 2. Failure at one rear wheel : ABS/TCS/ESP control of both front wheels are inhibited and the pressure of both rear wheels are decreased. After the controller completes the ABS/TCS/ESP control, the ABS/TCS/ESP functions are inhibited. The ABS/TCS/ESP warning lamps are activated and the EBD warning lamp is not activated. 3. More than 2 wheels failure : System down. The ABS/EBD/TCS/ESP functions are inhibited. The valve relay and all solenoids are prevented from being switched on. The ABS/EBD/TCS/ESP warning lamps are activated. |
