I know a lot has been posted on this subject, but I was wondering, is there is an established sequence for checking the electrical components in the electronic 4 wheel drive system for a 1997 F150 Lariat? Here is the reason I ask. My truck had been sitting for a while and we had a significant snow fall. Hooked up the plow, shifted into 4H and cleared our drive. Since the roads were pretty crappy, left it in 4H and drove about 2 miles to my son's house and cleared his drive. Returning home I attempted to shift it back into 2W. I noticed the 4x4 light on the dash remained on and when turning at the corner realized even though the **** said 2W it was still in 4H. Checked the fuses under hood and the dash. All seemed good. Since the weather has been pretty nasty took the truck to the local garage. They said they would check it out and give me a call.
Here is what they told me. First they changed the transfer shift case motor. No change. They found no power to the motor and checked the continuity of the wires from the switch to the motor and it checked good. Next they replaced the selector switch on the dash. No change. Now they tell me it's problem the Gem module. I have been down this road before. About 3 years ago had some weird things happening on the dash and power windows and 4x4 would not engage. Bought a rebuilt Gem module and every things been good to now. (No windshield leaks or water damage). So I have some questions whether the Gem module would be bad again.
I asked them at the garage, before they replace the Gem module, if they could pull it, clean the contacts, check the fuse block for corrosion and try it again. I mentioned that there are relay modules in the system but they dismissed them.
I'm sure this is going to cost me a pretty penny in labor alone. If this last attempt to clean the Gem module contacts and check the fuse block don't doesn't work, I plan to bring it home and when we get some warmer weather work on it myself. Any help or suggestions would be appreciated. Looks like I'll be using the snow blower this winter.

 

I believe there's a vacuum component to the 4WD system, and, if my failing memory hasen't totally deserted me, a vacuum leak will "lock" the system in 4WD. With a truck that old, I'd check for this leak. Sadly, I don't know how you go about that, but I'm sure someone here does.I think it should be an inexpensive fix.

- Jack

 

Question is..is the front actually still locked?
If no, the problem is back at the Gem.
If yes, the front Actuator is still operated. Get under, remove the cover and take a look. The operation is a sliding splined sleeve coupling inside the housing.
.
If just the 4H light is on and not in 4H, the Gem lights the Lamp. Just turning the dash switch on to 4H does (not) light the lamp by that simple action.
None of this is blown fuses or open circuits.
Since the case motor was replaced, (and still in 2wd position) " an important clue" with 4H still lighted, the Gem is keeping it lighted. for some reason.
The above two functions has to be checked to see what section is at fault.
You got here because your shop did not know but just guessed.by not knowing the complete operation of 4wd..
It's not simple with a module involved.
Good luck.

 

Thank you for your response. Something to consider.

 

Thank you Bluegrass. You present some good questions and options to try when i get my truck back!

 

This video may help.

 

Thanks Roadie, very helpful video.

 

Picked up the truck today. Still locked in 4H. Disconnected the positive post then hooked it back up. Hopped back in the cab, started it up then switched to 2WD, Low and behold I heard the clicking. Took her for a ride. As far as I can tell it went into 2WD based on steering when turning. When I stopped at the corner and switched back to 4H. Immediately noticed a difference in steering. Pulled onto a large patch of ice and tested traction in 2WD and 4H. Appears to be working so far. Hopefully it will last to better weather when I can do a proper diagnosis. Thanks again to all for your suggestions.

 

While driving today encounter a new issue with the 4x4 system. As road conditions today are nasty, I attempted to switch from 2WD to 4H. The 4x4 light immediately came on, clicking under the dash when turning switch, but high whining sound came from underneath the cab. I switched it back to 2WD and pulled off the road. While sitting still I again attempted to switch into 4H. Again light on dash, clicking under dash but this time no noise under the cab. Drove back home with 4x4 engaged. Pulling into our drive switched back into 2WD no problem. Obviously, somethings going on. Could it be related to my previous problem? Any thoughts?

 

when it isn't working properly, test it like the video shows.

 

Will do. Just wonder if anyone else had this occur.