DTC P0731: A/T 1ST Gear Function: Description: Notes

This is an OBD-II self-diagnostic item and not available in TCM self-diagnosis.
This malfunction will not be detected while the O/D OFF indicator lamp is indicating another self-diagnosis malfunction.
This malfunction is detected when the A/T does not shift into first gear position as instructed by the TCM. This is not caused by electrical malfunction (circuits open or shorted) but by mechanical malfunction such as control valve sticking, improper solenoid valve operation, etc.

Fig 1: Malfunction Detection Chart
Courtesy of NISSAN MOTOR CO., U.S.A.