Four-wheel drive not working

2002 FORD F-150
205,000 MILES • 5.4L • V6 • 4WD • AUTOMATIC
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JMAC75
  • MEMBER
  • 1 POST
When I turn knob to 4hi the 4hi light comes on and the vacuum changes to the passenger side solenoid at the firewall, but I hear nothing from the transfer case, and I have no 4wd. If I switch to 4lo only the 4hi light comes on and the transfer case does not go into low range and still no 4wd. When I return the switch to the 2hi position the 4hi light stays on and the vacuum solenoids on the firewall do not switch back. Only if I disconnect the battery will the 4hi light go off and the vacuum solenoids return to driver side vacuum.
Feb 28, 2022 at 10:45 PM
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KASEKENNY
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 18,907 POSTS
We need to start by checking the voltage coming from the switch going to the GEM.

Then we need to check fuse 104 in the battery junction block. This is what feeds the relays for system.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Lastly, we need to find out if the GEM is grounding the relay. This is the orange and light blue wire that is highlighted below.

The way we do this is put your red meter on battery positive and then the other on this wire. Engage the 4x4 and see if the meter reads battery voltage. If it does, then the GEM is working.

However, I suspect the GEM is going to be the issue so let's run through this and let me know what questions you have.

Thanks.
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Mar 2, 2022 at 11:41 AM