While driving, I heard a click behind the dash similar to the click that occurs when switching into 4WD. At the same time, I heard a rumbling from the front end and a binding on tight turns consistent with the front differential being locked. I do not know if the transfer case was locked or not.

When the problem first occurred, I had the dash switch in the AWD (i.e. 2WD) position. I tried changing it to 4HI, but the 4x4 light would not come on. I tried shifting into neutral and reverse and it did not change the symptoms.

The problem persisted until I got home. However, I turned the engine off, and immediately restarted it, and the problem was gone and the 4x4 light operated normally.

I just completed a search of old posts and I think I understand how the 4WD system works on these vehicles, but I cannot explain these symptoms:

1) I'm not certain, but I'm guessing that the clicks I heard behind the dash were the vacuum solenoids for the front differential. If so, what could cause them to switch spontaneously?

2) Why would the 4x4 light not come on when I put the switch into 4HI? Does the dash switch directly control the transfer case motor, or is there some other series of conditions that must be met before it is commanded to shift?

3) Why would shutting the engine off and starting it again reset the problem?

This problem has occurred twice in the past week, so I assume it will happen again until I find out what causes it.

Thanks.