P0840 - nissan maxima2008 16800 miles

Question

po 840 transmission fluid pressure sensor switch a.after show dtc 1778

Answer 1

The P0840 code is for the Transmission fluid pressure sensor A  and the P1778 for the Step Motor, I'm not sure what the codes have in common, but since your Maxima is 2008 and with only 16,800 miles you should have the dealer check it for you under warranty.