A vehicle that will not shift into four-wheel drive may have a mechanical or electronic problem somewhere in the engagement system. Depending on the vehicle, possible areas of concern include the transfer case, hubs, switches, actuators, sensors, wiring or computer controls.
Repeatedly trying to force the system into 4WD does not identify or correct the cause. Certified Transmission in Bellevue can diagnose the complete system and determine why four-wheel drive is not engaging.