DTC P1815: M-Mode Switch: Description
WARNING: This page is about a different car, the 2012 Nissan Pathfinder. However, it is still accessible from the selected car via links, so may be relevant.
Manual mode switch is installed in A/T shift selector. It sends manual mode switch, shift up and shift down switch signals to TCM.
TCM sends the switch signals to combination meter and A/C amp. by CAN communication line. Then manual mode switch position is indicated on the A/T position indicator.