I have a 98 f150 auto trans with the electronic 4WD selector. After using it a few times this weekend to pull my boat out of an unimproved ramp it started acting funny the next time I selected it. It would not engage in hi or low although the 4WD light did come on, and would not go off regardless of switch position. The switch is not making the relay or solenoid noise it used to make either.
I checked the fuse in the eng compartment, found it still good and replaced it, and this turned off the 4WD light. Next I tried to engage 4WD hi at about 30mph. Heard a mild grinding noise like gears trying to mesh but out of sync. I slowed down and swithed it off. Got the 4WD light again even with switch off. Pulled and replaced fuse to make the light go out. Does this light have a fault reporting function?

Now the system will do nothing and the fuse is still good. I suspect some sort of relay or solenoid is malfunctioning but I am unfamiliar with this system. Are there any troubleshooting guides available, it has been a long time since I looked at a Chilton's manual but that is my next option.

 

Not sure how much help I can give ya but I have seen posts of this problem before. Most said they had to take their electric motor off the transfer case and clean it up, they said the brushes needed cleaning in most cases. Maybe try to search for this topic. As far as I know the transfer case does not have a diag light, the O/D light on the gear selector will flash if there is a tranny problem.

 

FYI,

thank you for replies, I used my buddies service manual to troubleshoot the problem. When I got to the test using a scanner I had to skip over them.

The solution to the malfunction must have been some corroded contacts on the harness that connect to the shift motor. All I did was remove it (it looked clean) and reconnect it. It all works like new now.

I am going to put some electrical grease in the connector before winter hits.