Sometimes a light bulb is your go-to test equipment. jbrickey had a Ford F250 pickup in their shop that would immediately set a transfer case code of P1839 that would set any time you would change the 4WD selector switch. They posed the question to the community, and with the help of fellow community member powerstroketech and others, they were able to resolve the issue.
The following Real Fix summarizes the interaction between them in the community that led to the solution.
Vehicle
2011 Ford Pickup F250 Super Duty 6.2L
Title
P1839, Replaced Transfer Case Shift Motor
Complaint
P1839 will set as soon as you change the 4wd selector.
Diagnostic Steps Performed/Parts Replaced
Tested wires from transfer case control module (TCCM) connector to transfer case motor. Both have less than 1 ohm. Replaced TCCM and no change.
Best Answer from Community Member powerstroketech
Use a headlight in place of the shift motor. Clear the dtc and switch from 2wd to 4wd and see if the light will illuminate. If so, you have a faulty shift motor!
Cause
The headlight trick worked. Cause is bad transfer case shift motor.
Correction
Replaced transfer case shift motor and vehicle operates as desired.
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