My brother owns a 2002 F-150 4X4. It has a standard transmission and a manual shift lever on the floor for the 4X4. A few days ago, the 4X4 light came on in the dash. The lever was in the 2 wheel drive position. He shifted it into and out of 4x4 a few times and the light went out, only to come on again on its own. He noted that when the light was on, he could feel in the steering wheel when going around a sharp corner at a very low speed on dry pavement that the front end was engaged. When the light was out, there is no binding felt in the steering wheel. He crawled under the truck and sprayed what he thinks was the 4X4 linkage with a copious amount of WD-40. It made the lever shift smooth but did nothing towards putting the light out. The light comes on and goes out on its own accord. He is temporarily living on the other end of the State, a long ways from his trusted mechanic. He took the truck to a local repair shop and had the front drive shaft removed to prevent any damage from being done as he needs the truck to travel to work. Does anyone have any ideas as to what might be wrong. Thanks in advance.

 

Removing the drive shaft was over kill but they did what he requested.
The system is getting the signal falsely to engage.
If it should go into 4L he will have another issue because the transmission shifting will be away from normal shift points/rpm.
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It could be a case of windshield leakage onto the GEM module under the dash or some other cause that results the same action.
Knowing how the system works is the key to trouble shooting.
All that would be needed to stop the 4wd action was to remove the plug from the transfer case motor or even remove the plug from the firewall relay once the system was back to 2wd.. This is the point that signals the dash light to come on.
The firewall relay transfers engine vacuum to the front axle actuator locking the axles together.
Or removing the vacuum lines off the actuator and being sure the axles are unlocked would do the same.
Apparently the total systems is ok but getting a false signal to operate.
Info to work with, good luck.

 

I don't believe that his truck was actually in four wheel drive when the light was on. I believe that it was only the front differential that was engaged because even with the drive shaft removed, he can still feel the binding in the steering wheel when the light is on. Where he has a manual shift lever for the transfer case and an electric/vacuum shift for the front differential, might it be something as simple as the switch that screws into the transfer case?

 

Ok I failed to get that.
If that is the case the Actuator is stuck, engaging the locking collar.
He has to get under and release the actuator to unlock the axles for whatever it takes to do it..
Put the drive shaft back in place since it does not help to have it off.
Good luck.