Sorry for replying late, i faced this problem and i fixed it by doing the correct diagnostic. So firstly, i switched on my truck and start riding with the lane departure warning system is activated. Then i turn right i felt the vibration, next, i turned left and suddenly the vibrate alert turned into sound alert. then i removed the seat cover and checked the vibrate motor i found that the harness was cut i pick it out, reconnect and elongated the wore and reinstall it. so its working fine.
Mechanic Eng. interested in automobiles especially GM trucks since 2000