My 03 F250 6.0 diesel is stuck in 4 low and I can't get it out. I have cleaned
switch on dash, cleaned relays, did all the tricks I read about online like
going in reverse and stomping the brake then switch to neutral and none of
It works, my air while on Max AC will go to defrost on its own
is this related to the 4 low being stuck

 

Yes, it is. Its a vaccum leak more than likely. One of these other guys will chime in that can help you diagnose it better. Best of luck to you.

 

the air switching from a/c vents to defrost vents indicates vacuum leak. 4x4 is also vacuum actuated hubs. check hoses on front hubs 1st. best and fastest way to find a vacuum leak is by injecting smoke and watching where it leaks from. i'm not talking that kinda smoke either....but make sure you do the scented type or the vehicle will smell like a dirty ashtray.

Is this manual or auto shift on the fly?

make sure your hubs are unlocked and 4x4 disengaged

next jack it up with both wheels off the ground, use jack stands and try to rotate the drive shaft where it comes from the transfer case.

if it spins then the transfer case is disengaged and the problem is in the front hubs

if it is a shift on the fly type hub you could add a vacuum at the hub and bypass all the lines internally so to speak.

connect vacuum pump with a t fitting and plug ones coming from vehicle pump to see if that way works to get hubs to unlock

if manual hubs rotate the tires one at a time frontwards and backwards to see if the axle turns when you are turning the wheel. if it turns when you are rotating the wheel then the hub is still engaged even if you set it to the unlock position. try switching it back and forth from lock to free a few times.

i had a similiar issue with my 07 f250 and it turned out to be a bad hub but hope that yours is not....

i would also check your vacuum pump to see if it is working

 

The service manual discusses electronics under the hood that control the engagement of the transfer case (motor on the side of the transfer case). Check the two relays by the drivers side battery . They are in a small box 1.5"x3". They are for the shift motor. You can spray some contact cleaner in the plugs to get any gunk or oxidation out.

Verify power to the 4x4 switch and or check for a blown fuse or unplugged connector. If all that checks, out go to the tcase motor and verify power to it and that it is infact switching the tcase. I have heard that these motors on the tcase are fairly reliable so it may very well be either a pulled wire or loose connection .

 

A friend of mine had a new electric motor for transfer case
and I put it on all connections are good have voltage to it and
still not working. Took it out of 4 low and left motor off untilled
I figure this thing out. I am told there is a electronic box
under the glove box that could be my problem. Anyone heard of it

 

I have heard that box it could be the GEM Module

There are some 4X4 shift relays what engauge that moter to make it shift

IMO if its stuck in 4Low that has NOTHING to do with Vacum or Hubs you can have hubs locked in that has no affect on 4hi or 4low gearing

The Problem is in the Tranfer case or Moter or Electronics that control the Moter ie relays ect...

I have some stuff on diagnosing it IIRC hang on I will try to post

 

The electronic shift on the fly (ESOF) system is an electronic shift system that allows the operator to choose between 2 different 4x4
modes as well as 2-wheel drive. The operator can

switch between 2H and 4H mode at speeds up to 88 km/h (55 mph). To engage
or disengage 4L, the 4x4 generic electronic module (GEM) requires that the vehicle speed be less than 5 km/h (3 mph), the brake
pedal pressed and the transmission in NEUTRAL (or clutch pedal applied on manual transmission vehicles). This system contains
pulse vacuum hublocks (PVH). The selector on the hublock, when turned fully counterclockwise to the AUTO position,
engages/disengages the hub depending on the driver-selected 4x4 mode of operation. The hublocks also contain a manual
override. When the selector is rotated fully clockwise to the LOCK position, the 4x4 vacuum and electronic system used for coupling
the front axle to the wheels is bypassed.
The transfer case is equipped with a dual-cone synchronous clutch. This clutch is used to synchronize the front driveline to the rear.
All other internals operate in the same manner as the manual shift system. When the mode select switch (MSS) on the instrument
panel is turned, the 4x4 module powers the transfer case shift motor, which activates a shift fork and engages the clutch. When the
shift motor reaches the desired position, as determined by the encoder position inputs to the 4x4 module, power to the shift motor is
removed. When the transfer case front and rear output shafts are synchronized, the lockup collar mechanically engages the

mainshaft

hub to the drive sprocket. At this point, the front axle PVHs are engaged. Instrument cluster "4x4" and "Low Range"

indicator operation is controlled via hardwired outputs from the 4x4 module.

The New Venture

Gear NV 273 electronic shift transfer case is a 3-piece aluminium design. The unit transfers engine power from
the transmission to the front and rear axles. Under normal driving conditions the unit is in 2-wheel drive high (2H), but when desired,
the operator may shift into 4-wheel drive high (4H) or 4-wheel drive low (4L). The transfer case is shifted electronically. The unit is
lubricated by a positive displacement fluid pump that channels fluid flow through holes in the mainshaft.
The encoder assembly used for mode indication is of a Hall-effect type. The system uses a total of 4 independent transistors for
mode recognition. Each transistor is associated with a specific range of motor movement. When the circuit to each transistor is
closed, a ground path to any of the A, B, C or D encoder pins is accomplished. When the circuit to each transistor is open, the
connection to any of the A, B, C or D encoder pins is pulled to voltage. Mode indication is "decoded" by the 4x4 module based on

the varying combinations of signals coming from the transistors

 

4HI is more forgiving to shift in and Out

The conditions for shifting in and out of 4X4 LOW is very precise ALL Conditions must be Met Exact as in truck STOPPED in NUETRAL with the BRAKE APPLIED and then you may Switch in or out 4LOW all steps must be done in this order for 4Low engauge/disengauge

For a Shift Attempt From 2H to 4H or 4L, the Following Sequence Occurs:

MSS is switched from 2H to 4H or 4L
For shift attempts into 4L:
the brake must be applied.
transmission must be in NEUTRAL (or clutch pedal applied).
vehicle speed must be below 8 km/h (5 mph).
Shift motor moves range fork in transfer case, which engages dual-cone synchronizers
If a blocked shift condition occurs, the shift motor will perform 10 shift attempts (2H to 4H or 4H to 4L) totaling 5 clockwise
movements and 5 counterclockwise movements with an approximate 1-second delay between each motor movement attempt
If, after 10 attempts, a shift is not completed, then the module will command a shift motor rest time of 40 seconds, before it
attempts any further shifts
After the 40 seconds have expired, the motor will make 10 more attempts to complete the shift. The motor will continue to
repeat this sequence a total of 6 times (60 shift attempts) before ceasing operation. No further shift attempts will be made,
nor will any further MSS commands be recognized. The vehicle must be restarted for 4x4 function to be restored. If this
occurs, DTC C1728 (for 2H to 4H attempts) or DTC C1729 (for 4H to 4L shift attempts) will be stored in memory
If the vehicle is driven above 5 km/h (3 mph) during a 40-second rest period, the module will reattempt the shift strategy
outlined previously. Generally, the transfer case will engage as the probability of

gear teeth blockage is greatly reduced
while rolling
If no gear teeth blockage is present, the transfer case synchronizers bring the front driveshaft to same speed as rear
driveshaft

Shift fork

completes movement and the "4x4" and (if 4L) "Low Range" lamp will illuminate. This ONLY occurs when the
driveshafts are synchronized. If they are not, then the "4x4" lamp will not illuminate
Once the 4x4 lamp is illuminated, the PVH lock and lock/unlock solenoids are energized for 45 seconds, with approximately
62 kPa (9 psi) of vacuum or more at the hubs. The PVH lock sequence cannot be overridden at any time (a mode shift
change back to 2H)
After 45 seconds have elapsed, the solenoids undergo a 6-second vent period, whereby no commands to either the lock or
lock/unlock solenoids are allowed, regardless of MSS position
If the vehicle is driven above 8 km/h (5 mph) the PVH lock and lock/unlock solenoids are re-energized in the same manner,

regardless of whether the hubs are engaged or the original 45-second engagement timer has expired

For a Shift Attempt from 4L to 4H to 2H, the Following Sequence Occurs:

4x4 mode select switch is placed from 4H or 4L to 2H
For shift attempts out of 4L:
the brake must be applied.
transmission must be in NEUTRAL (or clutch pedal applied).
vehicle speed must be below 8 km/h (5 mph).
Shift motor moves range fork in transfer case, which disengages dual-cone synchronizers
If a blocked shift condition occurs, the shift motor will perform 10 shift attempts from 4H or 4L to 2H to 4H or 4L to 2H totaling
5 clockwise movements and 5 counterclockwise movements with an approximate 1-second delay between each motor
movement attempt
If, after 10 attempts, a shift is not completed, then the module will command a shift motor rest time of 40 seconds, before it
attempts any further shifts
After the 40 seconds have expired, the motor will make 10 more attempts to complete the shift. The motor will continue to
repeat this sequence a total of 6 times (60 shift attempts) before ceasing operation. No further shift attempts will be made,
nor will any further MSS commands be recognized. The vehicle must be restarted for 4x4 function to be restored. If this
occurs, DTC C1728 (for attempts between 2H and 4H) or DTC C1729 (for attempts between 4H and 4L) will be stored in
memory.

If the vehicle is driven above 3 mph (5 km/h) during a 40-second rest period, the module will reattempt a shift (4H to 2H

only). Generally, the transfer case will disengage as the probability of torque trapping is lower while rolling
If no torque trapping is present, the transfer case synchronizers decouple the front driveshaft

Shift fork

completes movement and de-energizes "4x4", and if 4L, "Low Range" lamps. Once the 4x4 lamp is de-energized,
the PVH lock/unlock solenoid is energized for 15 seconds, pulling approximately 41 kPa (6 psi) of vacuum at the hubs
The PVH unlock sequence can be overridden at any time such as a mode shift change back to 4H or 4L, relocking the hubs
After 15 seconds, the solenoids undergo a 6-second vent period; the vent period can be overridden at any time by a shift

attempt to 4H or 4L.

 

No my question what did you do to get it out of 4LOW???

 

I pulled electronic motor off the transfer case and used a wrench to manually shift it out

 

you can also pull the electric connector off the motor which controls the tranfer case and use a battery charger capable of 10 amps to drive the motor back to the 2 WD position. There are only two wires and connecting the polarity one way drives the motor to 4 WD and reversing the polarity drives the motor back to 2 WD. Note you can check the function of the electric motor this way and also watch the indicator in the cab change as the gearing changes.

When I had a problem in this area it was the relays in the black plastic box between the left fender and the driver side battery which houses the two relays for controlling the tranfer case motor. The box was mounted upside down (yes if you really try you can mount it upside down) from the factory so the drain hole was at the top which allowed road splash and condensation to collect inside the box causing one relay to corrode and quite functioning. Note that the first two replacement relays I got from the dealer were also defective right out of the box!

If only one relay is bad you can reverse them to drive the motor back to the 2 WD position (you will not be able to put into 4 WD until the defective relay is replaced though).

 

Thanks for all the help

 

BASIC INFO BELOW Keep in mind FORD Relays can be Numbered diff than this Info Im posting but they operate the Same

TROUBLESHOOTING INFO RELAYS
-a standard bosch-style relay will have 4 or 5 numbered leads (30, 85, 86, 87, and sometimes 87a). why they picked those numbers, I have no clue; but I can tell what they hook up to.
-30 = constant [positive (+)] power (usually wired directly to car battery)
-85 = coil ground (wired to the negative (-) battery terminal or any grounded metal panel in the car)
-86 = coil power (wired to the control source. could be a switch, or it could be the car's IGN or ACC circuit.)
-87 = switched [positive (+)] power output. (when the relay coil is powered, lead/pin 87 is connected to lead/pin 30)
-87a = [on 5 lead/pin relays only] this lead/pin is connected to lead/pin 30 when the coil is NOT powered.
here is the bottom view of a standard 4-lead Bosch-style automotive SPST relay

here is what happens inside the 4-lead/pin SPST relay. on the left, the coil is NOT powered. on the right, the coil IS powered. notice the switch changes positions when the coil is powered. when the coil is powered, pins 30 and 87 are connected. when the coil is NOT powered, then pin 30 is not connected to anything, therefore it is in the 'off' position.
Click this bar to view the full image.




TROUBLESHOOTING VIDEOS
---------------------------------------------------------------------------------------
1.HOW TO TEST A RELAY
http://www.youtube.com/embed/3JB63ebFfgU

 

Thanks for the information about the four wheel drive. Think I have it narrowed
Down to a couple things. But I have bigger problems now. On my way to work this
morning my truck quit on me. Will turn over but will not crank. Put my runner on it
to check the codes and the one that stood out was low injector pressure. So I am wandering if that is going to be my high pressure oil pump or a fuel pump

 

Was it P2285 ??????????????????????????

Unplug your ICP Sensor and try to start the truck

03 its under the Turbo

Its going to be a HIgh Press Oil Problem
Not Fuel delivery

and the exact DTC would help