my front left hub would occasionally partially engage while I was driving. if I stopped it would release. this would only happen once in awhile. I figured it was a leak in the hub seal. took it to ford because I thought I still had some extended warranty left. $120 later they told me it was a faulty iwb solenoid. rock auto and $21 later so far so good. figure I share this info for others who may have a similar issue.