The Ducati ABS brake system manages the front and rear brakes separately. A pulse generator (phonic wheel), with a ring of slots, is fixed onto each wheel. On the left calliper mounting bracket of the front fork and on the rear brake calliper holder plate are HALL effect sensors which detect the full sections and voids on the phonic wheel as the vehicle moves, providing and instantaneous wheel speed reading. These sensors transmit the data to the ABS control unit, which contains software implementing a specific control algorithm developed by Ducati. The software compares the average speed of the vehicle against the instantaneous wheel speed values to determine the degree of skidding. If the pressure applied to the calliper by the rider causes the control limits to be exceeded, the control unit intervenes in the braking circuit relative to the wheel for which incipient lock-up is detected. The ABS modulates the calliper pressure with a system of solenoid valves that initially prevents any further increase in hydraulic pressure (EV valve closed), and then reduces pressure (AV valve opened). The AV valve is opened in a series of pulses (with less than 10 milliseconds between successive pulses), to reduce pressure in steps. When the wheel begins to rotate again in response to the diminished braking force applied and the wheel speed reaches the reference value, the AV release valve is closed.
While ATT indicates that the error has been diagnosed during the current test session, it does not necessarily indicate that the error is actually active at the time of indication. For example: disconnecting the front wheel speed sensor causes the code ATT to be displayed after the error description, but the code continues to be displayed even once the cause of its activation has been eliminated by reconnecting the sensor, as the ABS will only check sensor operation again after the next key-off/key-on cycle. As a result, always perform a key-on/key-off cycle after any work on the ABS system, interrupting and reopening communication between the diagnostic instrument and the ABS control unit before checking the updated ABS error list again.