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Scottdagoalie, Senior Master Tech.
Category: Ford
Satisfied Customers: 1940
Experience:  30 years with Ford dealers
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2002 f250: four wheel drive low and it will not switch

Customer Question

2002 f250 switched to four wheel drive low and it will not switch back toXXXXX stuck in low. help!
Submitted: 8 years ago.
Category: Ford
Expert:  Scottdagoalie replied 8 years ago.
HiCustomer Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way,
Is this a manual shift or electronic shift transfer case?
Customer: replied 8 years ago.
manual shift. i changed the selector switch nothing! still stuck in 4 x 4 low
Expert:  Scottdagoalie replied 8 years ago.

The problem is in the shift fork in the transfer case. Just had a similar problem two days ago with the same symptom.The Shift fork wears out and binds when trying to move gear slide. Transfer case will need rebuild.

You say you've changed the selector switch>? The manual shift transfer case has a shift lever on the floor to engage 4X4.The electronic shift has a 'selector switch'.

If you have electronic shift, then you probably have a actuator motor on the transfer case that may be binding.Let me know if this helps and if you need more answers.

Customer: replied 8 years ago.
okay it has too be electronic then. on what side is it how big should it be
Expert:  Scottdagoalie replied 8 years ago.
The actuator is located on the left side of the transfer case(drivers side).Below is a picture to help.With this system,it could still be a shift fork problem.After you remove the actuator,attempt to move the shift cam on the transfer case.If it doesn't shift smoothly,then the fork in the transfer case is the problem.If it does shift ok,then there is a problem in the control portion. Let me know if this has helped.graphic
Customer: replied 8 years ago.
Expert:  Scottdagoalie replied 8 years ago.
Keep me posted.Please check the accept tab if this information has been of any help.Thank you!
Customer: replied 8 years ago.
i took the actuator off and moved the small cam on it, when i did that the matching piece on the transfer case moved as well
Expert:  Scottdagoalie replied 8 years ago.
Did that take it out of 4 low? If it did,the control unit is not operating properly.
Customer: replied 8 years ago.
okay thanks where is the control unit, and is there any way to check
Expert:  Scottdagoalie replied 8 years ago.
The actuator motor you removed is part of the control system ,which is commanded to move by the 4x4 module.You will need a scan tool that is able to check this module for trouble codes. This would be the ideal place to continue your 4x4 diagnosis. You can also change your selector and visually monitor the actuator motor to see if it's moving the transfer case shift cam. But you were able to get truck out of 4 low?
Customer: replied 8 years ago.
no, when i moved the actuator the transfer case shift cam moved. i may have moved it back to the low setting. the only thing is that the 4x4 light is off on the dash board. and it is still in 4x4 low
Expert:  Scottdagoalie replied 8 years ago.
Ok,I misunderstood your previous coment. If you moved the cam and it's still stuck in 4 low,the problem is in the shift fork inside the transfer case. The transfer case will need rebuild.
Scottdagoalie and other Ford Specialists are ready to help you
Customer: replied 8 years ago.
no had to step away from it this weekend, will get back on it tuesday. but i will click aeccprt anyway
Expert:  Scottdagoalie replied 8 years ago.
ok, let me know if you still need help on this question. Thanks for the accept.
Customer: replied 8 years ago.
okay i a back have been sick. when i move the actuator on the side on the transmission i can c the cam move as well. what controls the actuator that is mounted to the tranny
Expert:  Scottdagoalie replied 8 years ago.
Glad that you're feeling better!
The transfer case motor is controlled by the 4wd module.

2002 F-Super Duty 250-550/Excursion Workshop Manual

Principles of Operation

Transfer Case — Electronic Shift

The four-wheel drive, electronic shift-on-the-fly feature electrically shifts the vehicle transfer case between 2WD, 4X4, and 4X4 LOW. The system mode is selected by the operator through the mode select switch (MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument cluster indicators, one for 4X4, and one for 4X4 LOW in 4X4 LOW both the lamps are on). Shifts into 4X4 can be made at any speed. When shifting into 4X4 with the vehicle stationary, tooth blockage may occur, preventing shift completion. When the vehicle is driven above 8 km/h (5mph) the shift will complete. When shifting in or out of 4X4 LOW, the four-wheel drive (4WD) control module requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and the transmission in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual transmission). (The digital transmission range TR sensor informs the 4WD control module when the automatic transmission is in the NEUTRAL range position.)

The gearmotor encoder assembly is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and the range fork within the transfer case between the 4X4, 4X4 LOW, and 2WD range positions.

The 4WD control module uses two relays to control the gearmotor encoder assembly shift between 4X4, 4X4 LOW, and 2WD modes. The 4WD control module controls the pulse vacuum hublock (PVH) solenoid which supplies engagement and disengagement vacuum to control the hublocks.

The 4WD control module accomplishes shifts by interpreting inputs from:

  • MSS
  • vehicle speed signal (transmitted from the ABS system)
  • gearmotor encoder plate position
  • brake pedal switch
  • digital TR sensor (automatic transmission)
  • clutch pedal position (CPP) switch (manual transmission)
  • ignition switch

Based on these inputs, the 4WD control module controls the shifts into 2WD, 4X4, or 4X4 LOW with the following outputs:

  • low to high relay (clockwise)
  • high to low relay (counterclockwise)
  • pulse vacuum hublock (PVH) solenoid
  • gearmotor encoder assembly

The electronic shift-on-the-fly (ESOF) system has a feature which allows the driver to override the vacuum-operated hublocks. When the front hublocks are manually turned to the LOCK position, the hublocks are locked at all times, overriding the vacuum operated system. If the front hublocks are manually turned to the AUTO position, the hublocks can only be locked by turning the MSS to 4X4 or 4X4 LOW position.

Electronic Shift Vacuum Schematic