My 1996 F250 with E04 trans will not upshift when transfer case is in low range. Once in a while it works fine, most of the time the trans will stay in low gear. In high range or 2WD, the transmission shifts fine. I don't understand the relationship, the transmission does not know what range the transfer case is in, does it?

 

Does the low range light on the dash light up?

If not the low range switch is probably the problem, if the light does light check the circuit low range switch to pin 12 PCM (Lt blu-blk wire).

Changes shift schedule for low range, computer doesn't know low range has been selected it doesn't shift soon enough.

 

The transmission does not, but the computer sure does AND the E4OD transmission is 100% computer controlled. Pin 12 on the PCM connector is the signal from the transfer case low range switch to the PCM.

As Dan asked, does the 4x4 Low Range light on the dash light up?

 

The low range light will illuminate in low range and will sometimes stay on even when back in 2WD. The transfer case is in 2WD, light still says 4 low.
Thanks in advance for the expertise.