Diagnostic code P0725 indicates that the PCM (Powertrain Control Module) has detected a fault in the VSS (Vehicle Speed Sensor) input signal circuit, this may be due to an electrical or mechanical problem.
The Vehicle Speed Sensor (VSS) is usually located in the gearbox, it is close to the front of the input shaft. Its position makes it work as a seal with the transmission box because this sensor has an electromagnetic hall effect, it is positioned to allow a toothed ring to pass close to its magnetic tip, which is attached to the input shaft of the transmission so that when the shaft is rotated, the two are rotated together. The raised areas of the teeth function as an electromagnetic complement to the motor speed input circuit, while the lowered areas between the teeth suspend the circuit.
These fast suspensions create an electromagnetic waveform pattern that represents a particular frequency and degree of voltage, this is defined by the Powertrain Control Module (PCM) as the input speed of the motor. If the PCM does not recognize the appropriate motor speed input signal for a certain period and under certain circumstances, the DTC code P0725 is established.