2005 Nissan Nismo Frontier 4wd not working

There may be a scan tool for the tranny only , it's better to diagnose than to replace parts nilly willy , you can buy test equipment for the price of a sensor you don't need ., perhaps take it to a good shop

The 4WD Warning light turns ON when ignition switch is turned to ON position and will stay ON if a malfunction has been detected by the system. differences between the diameters of front and rear wheels will make the warning light to come steady ON. Check: Clutch fluid and transfer case Oil level and conditions. with the Frontier stopped, shift the shift lever to the N position with the clutch pedal depressed and shift the 4WD shift switch to 2WD. If the warning light is still ON after this operation check, have your vehicle inspected as soon as possible by a Transmission Technician. thanks