First off this is a great site, I've used it alot before posting this. I'll describe problem and list some testing I've done.

I have a 2002 4.6L Lariat ESOF.
The 4x4 light is on but it is not engaged. Moving the selector switch has no effect.
With the key in on position there is no sound of relays or TC engagement under the truck. perfectly quiet.
Tested selector switch and showed proper OHM levels on pins 2 and 3. 3.8k 2wd 1.06k 4hi
Both Solenoids on firewall have suction on lower hoses with engine running

Key on:
Both solenoids show aprox 70 ohms accross pins.
using test light both solenoids have 12V.
BOTH solenoids FAIL ground switch test with dash selector switch in all positions.

so something is preventing GEM from sending ground switch signal to open solenoid and nothing from transfer case
hoping its a fuse or relay? I get no other dash alarms and everything else on truck works properly.

what fuses and relays should I check?

hopefully don't need to replace GEM or dig out Shift relay module under dash.

Thanks in advance for any help!

also this video was helpful in running most of these tests.

 

I would check the following:

Fuse #23 by hood lever inside of truck.
Range sensor switch.

 

Thanks Manual-
Thats the only fuse I checked and it was ok. sorry forgot to list!

 

Also I haven't checked anything under the truck yet since I'm not getting anything at all. Is that a correct assumption? can a faulty iwe or tc effect the relays at the beggining of the process?

 

No IWEs on the 2002.

 

cool thanks. One less thing!

 

Also tested fuses 111, 104, 23,20 and 6. all good
Since its 16 years old I'm thinking about wiring around the GEM to engage TC motor. As little as I use 4x4 doesn't make sense to spend alot or tear out dash.

 

Thanks for the video link!

 

You're welcome-

I tapped in the ground wires on the vac solenoids and forced them to ground. 1 clicked as expected and 1 didn't. I'm assuming that one is defective.

as soon as temp outside gets above single digits Im gonna jack up front end and spin wheels and check actuator.

Still think electrical/GEM issue since bad solenoid shouldn't kill all relays and tc movement.

 

You need to better understand the system operation.
Going forward, the dash switch 'requests' the GEM to run the transfer case motor to its first position.
This engages the transfer case, puts a ground on the firewall solenoid, transfers vacuum to operate the Actuator to engage the front axle.
At this time it is a signal to the GEM to operate the dash lamp.
If the transfer case is not engaged nor the front axle, the Gem has the light turned on.
There may be a windshield leak that has corroded the GEM module. It can't do any other operation in this condition.
Good luck.

 

Thanks Bluegrass-

Understanding that flow if very helpful. So I guess your saying its probably a bad GEM or something in the TC that is causing the GEM to be suspended in this state?

When it warms up some I'll do more. looks like snow is over for now and I'm too old to freeze!

 

I have a 97 that I'm having same issue with, so what is IWE???

 

Integrated wheel ends - vacuum operated hubs. They are only on 2004 and newer. 2003 and earlier have a differential lock.

 

Thank you! (Sorry for cutting in on someone else's post...)