For Toyota 4runner, may also apply to tacoma and FJ cruiser with electronic shifting mechanism. The 4wd indicator lights blink constantly after selecting 4wd. It engages but center differential remains locked due to a sensor error or failure to engage fully. Mine was fixed by replacing the front 4wd actuator. The old part had the motor breather nipple broken off allowing water and dirt inside the motor case. Dorman p/n 600488. https://www.amazon.com/gp/aw/d/B077KB...