DTC P0731 A/T 1ST Gear Function: Description
WARNING: This page is about a different car, the 2008 Infiniti M45 and 2008 Infiniti M35. However, it is still accessible from the selected car via links, so may be relevant.
This malfunction is detected when the A/T does not shift into 1st gear position as instructed by TCM. This is not only caused by electrical malfunction (circuits open or shorted) but by mechanical malfunction such as control valve sticking, improper solenoid valve operation, etc.