ESP_a139 — Steering Angle Wrong Sign
Full alert identifier: ESP_a139_steeringAngleWrongSign
Alert description
Steering Wheel Position Sensor: Plausibility fault
Potential impact
May fault VDC/TC, ABS performance degradation
Set condition
This monitoring detects a wrong sign of steering angle signal. The yaw rate calculated from steering angle and the yaw rate calculated from the wheel speed sensors are compared. If the measured yaw rate fits to the model yaw rate positive integrals (IVzLwVA and IVzLwHA) are calculated but if the negative values fits the integrals will become negative. A fault is determined if the integral value is negative and forward driving is recognized. This fault will cause a release test in the following ignition cycle to assure that the sensor is build in correctly. This fault can also be caused by swapped WSS lines at one axle. It requires a release check in the following ignition cycle to prevent system release when the fault is still present. The conditions for release is positive integrals (IVzLwVA and IVzLwHA) > +180 deg.
Clear condition
Verify EPAS is awake, in good state, and there is traffic present on the bus. Review EPAS/DI alerts for other indicators of failure
Check other alerts
With Service Mode Plus enabled, open Service Alerts → All. Review the other alerts for clues to the cause of ESP_a139.