4x4 not working P1820

sagebel

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While looking for my miss I got a P1820 code yesterday. Truck will not shift into 4H or 4L. Checked a 30a fuse under the hood and two relays under the hood. If I ground the relays the motor will shift so I think it is in the GEM or the dash switch. How do I narrow it down?
 

JLDickmon

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ha ha ha..
you're in luck..
shoot me an email and I'll send you a PDF of the circuit.

that setup is a lot more involved than you'd think.

to start with, you need good fuses at positions 19, 13, 28 and the 30 amp'er in 17..
 
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sagebel

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All fuses are good. Disconnected the switch and all switch position resistance matches the figure. Does this mean I'm looking for a GEM?
 

sagebel

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Started ringing out each wire to the GEM module today. The brown/white wire (low to high control) has no continuity between the relay and GEM module connection.

I have a questin about the 4x4 module. The diagram has a transfer case shift module. I thought the 2000 trucks just have two relays under the hood. If I do only have the two relays, I think I found the problem.
 

JLDickmon

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Started ringing out each wire to the GEM module today. The brown/white wire (low to high control) has no continuity between the relay and GEM module connection.

I have a questin about the 4x4 module. The diagram has a transfer case shift module. I thought the 2000 trucks just have two relays under the hood. If I do only have the two relays, I think I found the problem.

yes, I'd say the open wire is the problem..
that wiring diagram is actually for a late 99 (my truck), so component locations might not quite be the same, but I knew we could get you going in the right direction by showing you how the circuit works..

check this thread as well
http://www.superdutydiesel.com/foru...-4x4-light-does-not-come-all-help-please.html
 
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sagebel

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Fixed it. Brown/white wire is broken somewhere in the harness. Ran a new wire and 4x4 now works. Now back to the miss. Thanks JL for the diagram.
 

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