DTC P1815: Manual Mode Switch: Description
WARNING: This page is about a different car, the 2003 Infiniti G35. However, it is still accessible from the selected car via links, so may be relevant.
Manual mode switch is installed in A/T device. It sends manual mode switch, shift up and shift down switch signals to TCM.
TCM sends the switch signals to combination meter. by CAN communication line. Then manual mode switch position is indicated on the A/T indicator. For inspection, Refer to "POSITION INDICATOR LAMP ".