On Board Diagnosis Logic

WARNING: This page is about a different car, the 2013 Nissan Armada. However, it is still accessible from the selected car via links, so may be relevant.

This is not an OBD-II self-diagnostic item.
Diagnostic trouble code "P1721" with CONSULT is detected when TCM does not receive the proper vehicle speed signal (input by CAN communication) from combination meter.