Seems that my expedition doesn't want to automatically engage the AWD anymore. It will shift into 4H or 4L but say on a wet road, rear will start to spin and front will not engage as before. I am figuring it must be a sensor, but not sure which one or location.

 

Please clarify - does the front engage in 4H and 4L?

 

can rotate the dial to 4H and 4L and can hear/feel it engage. Also the dash lights come on and do not blink as if there is a malfunction.