Hi guys have a 2014 Silverado 1500 5.3 recently I had my service 4wd light come on and I can not go into any 4wd only 2wd works when it first came on the light came on for a few start ups than my 4wd worked than the next day it went out and the service 4wd light came back on what are the common issues I should check for it to fix it?