Im currently working on a customers 2002 Ford Escape V6 4x4. It has 237,000mi on the odo. I work on it all day and fixed everything that was wrong with it and I have only one problem left. The 4x4 system is not engaging. I currently have it on a lift and tested it. I put it in neutral and switched it to 4x4 and then put it in drive and only the front wheels move. The only DTC this ca had was an evap leak which was caused by a broken gas cap. For the life of me I cannot figure this out. Just so you know I'm only 17 and am a student at LCTI. Any help would be much appreciated.