DTC P1574: ASCD Vehicle Speed Sensor: Description
WARNING: This page is about a different car, the 2010 Infiniti G37. However, it is still accessible from the selected car via links, so may be relevant.
The ECM receives two vehicle speed signals via the CAN communication line. One is sent from "unified meter and A/C amp.", and the other is from TCM (Transmission control module). The ECM uses these signals for ASCD control. Refer to "SYSTEM DESCRIPTION " for ASCD functions.