DTC P1815: Manual Mode Switch: Description
WARNING: This page is about a different car, the 2005 Nissan 350Z. 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 unified meter and A/C amp. By CAN communication line. Then manual mode switch position is indicated on the A/T position indicator. For inspection, Refer to "A/T INDICATOR CIRCUIT ".