hi guys ! my friend has a 2001 Chevy Blazer 4x4 and the 4 wheel drive won't work at all ! he changed the switch on the dash, I cleaned the module inside the kick panel and he change the piece with hoses going to it on top of the transfer case and still no 4 wheel drive ! what's next, the part under the battery ? if it's not that than maybe the transfer case is shot I told him ! any of you guys know what might be wrong ? I appreciate your thought on this ! thanks guys !