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I'm read thru every thread on virtually every forum and cannot find anything that dulplicates exactly what I have. I have looked over multiple schematics, but I'll admit I'm not the best about reading them.
2002 7.3, about 6 months ago, I needed 4wd, and no go, no indicators or anything, put it on the back burner, but here I am.
Symptoms-no dash light when on, no light on switch. I replaced switch thinking maybe bulb was burned out and not completing the circuit. Same issue. When you first start truck the 4wd and 4-lo lights come on in self test mode, so obviously they are ok. Both plugs at T-case were pulled loose and cleaned just in case. Replaced relays under the hood just in case they were corroded from lack of use. I get no click from the relays when switching between modes. All fuses test ok.Front shaft spins freely regardless of dash switch position.
Is it safe to say the path is from the dash switch to the GEM, from the gem to the dash indicator and the underhood fuses, then in turn to the t-case motor?
If that is the case I of course suspect GEM unfortunately, any other modules or anything else that can be tested? I have Forscan, but cannot find any way to test or trigger the system.
1. The Generic Electronic Module (GEM) provides the PCM with an indication of 4x4L. This input is used to adjust the shift schedule. A 5.0 volt module pull-up indicates 4x4H or 2WD
2. The Four-Wheel Drive (4WD) Control Module is located behind the glove box, maybe you could do some voltage testing there.
Make sure voltage is coming into the relays. Where it should be hot at all times.
I put in an F250 manual shifter with a modified linkage to connect to the electronic transfer case after chasing same problem for a while with no answers. I still have to manually lock the hubs, but if they are locked, it shifts on the fly just fine.
1. The Generic Electronic Module (GEM) provides the PCM with an indication of 4x4L. This input is used to adjust the shift schedule. A 5.0 volt module pull-up indicates 4x4H or 2WD
2. The Four-Wheel Drive (4WD) Control Module is located behind the glove box, maybe you could do some voltage testing there.
Make sure voltage is coming into the relays. Where it should be hot at all times.
Whelp, pulled the module from behind the glove box, just for grins, doesn't look like I'm gonna need to look much farther, gonna try to clean up and do some board repair if needed, worst case, I'll get a new one on order.
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