Bosch-Common Rail System – Vehicle speed signal
1 Wheel speed sensors
2 ABS module
The vehicle speed signal is determined by the Bosch common rail system via the wheel speed sensors of the ABS.
The signal from the wheel speed sensors is transmitted via the CAN communication bus. The PCM calculates the vehicle speed from this.
For the calculation of the vehicle speed, the wheel speeds of both front wheels are detected and an average value is calculated.
If one or both front wheel speed sensors are faulty, the signals of both rear wheel speed sensors are used and their average is used as the vehicle speed value. If a fault occurs to the wheel speed sensors (one or both), a reliable vehicle speed signal can no longer be transmitted via the CAN data bus.
The signal is used by the PCM to calculate the gear selected and as information for the speed control which is integrated in the PCM.
Effects of faults
increased idling speed
uncomfortable judder during gearshifts.
The VSS has only minor effects on exhaust gas emissions and does not exceed the EOBD limits. The vehicle speed sensor signal is, however, part of the freeze frame data and is therefore classified as MIL active.
Possible diagnostic trouble codes: P0500, P1934.