Wheel Speed Sensor: Description and Operation

4511 ABS Sensor (active speed sensor DF11s)







The ABS wheel speeds are now determined using so-called multipole seals directly at the wheel bearings instead of conventional impulse rotors. The speed sensors installed in the 911 Carrera/S are designated as "active speed sensors". Active speed sensors require an external power supply. The connection with the control module is established via a two-cable wiring. The active speed sensor is provided with power and ground by the PSM control module. The functioning of the sensor element integrated within the active speed sensor is primarily based on the Hall principle depending on the strength and direction of a magnetic field. In contrast to a Hall barrier, a magnetically active rotor is scanned. The sensor is controlled by the rotor with alternating polarity near the magnetic zero point. The current change is transformed into a speed signal and sent to the PSM control module by an electronic circuit in the sensor element.

SAFETY: Resistance measurement can result in destruction of the active speed sensor. Observe the installation position of the wheel bearing.

Do not subject the wheel bearing to strong magnetic fields.