If your vehicle is showing vehicle unexpectedly pops out of 4wd or awd while driving, here are the most likely causes and the parts you'll need to fix each one.
The electric motor responsible for engaging and holding the transfer case in 4WD becomes weak or its internal position sensor fails, causing it to slip back into 2WD under load.
AWD and 4WD systems require all tires to be nearly identical in diameter. Replacing only one or two tires causes driveline bind, forcing the system to disengage to protect itself from catastrophic damage.
Old or low fluid causes excessive heat and friction. In systems utilizing hydraulic clutch packs for AWD engagement, low fluid prevents the system from maintaining the pressure needed to stay engaged.
Particularly common on vehicles with a manual 4WD floor shifter. Broken mounts allow the drivetrain to twist excessively under acceleration, physically pulling the mechanical linkage out of gear.
The AWD control module relies on wheel speed data to distribute power. If a sensor drops out or sends erratic signals, the computer will often disable the AWD system as a failsafe.
Severe internal wear to the shift forks, mode hub, or transfer case chain prevents the gears from fully locking into place, causing them to physically pop apart under torque.