Check the wiring to the rear speed sensor.
You may find that it has broken or is shorting.
DTC P1715 Rear Wheel Sensor Circuit Malfunction (Rear Speed Sensor)
The rear speed sensor detects the rear wheel speed based on revolution of the transfer drive gear.
Its construction is the same as that of the front speed sensor .
The center differential clutch is controlled by the ECM based on the signals from the front speed sensor and rear speed sensor.
Rear speed sensor fault
Open or short in rear speed sensor
Check resistance between terminals RR+ & RR- of ECM. Resistance should be between 560-680 ohms.
If not, ECM may be bad.
Measure resistance between terminals 1 & 2 of revolution sensor. Resistance should be 560-680 ohms.
Measure voltage between terminals 1&2 of speed sensor when magnet is put close to the front end of the rear speed sensor then taken away quickly. the voltage should be around 0.5 to 3 volts.
If not, rear wheel speed sensor may be bad.