This is from a service gram from cat on this system, the same rules should apply to this nissan system so use your own interpretation here on how to proceed with the diagnosis.

They are using the diagnozer program to do the monitoring so you will have to find another way to monitor these signals.

DTC P22 or P-22; Shift Lever Error Signal.

This DTC can mean that no shift lever input signal was detected for 2 seconds of time after the shift was made. This code can also set if duplicated shift lever inputs are detected by rapid shifting of the lever (creates a phantom code through hysteresis).

This code can also be generated when the Presence Detection System (PDS) is activated with the seat switch open.

Operate the truck while switching directions ( normal switching ). If the code returns then inspect for actual 'on' and 'off' activation of the transmission (T/M) shift solenoids. View them from the VCM input monitor page. View the operation of the directional lever while switching directions. Now view the transmission directional solenoid current (mA) during directional switching. There should be12 VDC applied and then removed from the solenoids.
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Now, switch to the output monitor page. View the transmission (T/M) signal (neutral position) and then T/M solenoid "F" and then "R" while switching. If these are receiving input and output signals, then the system is working.
If one direction does not receive an input signal, check the wiring between the directional switch and the appropriate transmission shift solenoid. If there is a issue on the reverse side, you must also check the wiring from the reverse shift solenoid to the directional control and also to the backup alarm relay, fuse, wiring, etc.

good luck :o)