DTC P1574: ASCD Vehicle Speed Sensor: Description
WARNING: This page is about a different car, the 2012 Infiniti QX56. However, it is still accessible from the selected car via links, so may be relevant.
The ECM receives two vehicle speed signals by the CAN communication line. One is sent from "combination meter", and the other is from TCM (Transmission control module). The ECM uses these signals for ASCD control. Refer to "AUTOMATIC SPEED CONTROL DEVICE (ASCD): SYSTEM DESCRIPTION " for ASCD functions.