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HDGENE
HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 4784
Experience:  25 years Auto experience, Ford ,GM, Chrysler, Asian & European
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Won't shift out of 2wd. Ford 2000 f250 SD crew 4x4 gas v10

Customer Question

Won't shift out of 2wd.
Ford 2000 f250 SD crew 4x4 gas v10 manual tranny.
Verified all fuses good.
I've replaced the transfer case motor with a new one, verified the old and the new motors operate.
I've replaced the electric switch with a used one. The switch terminals show no voltage differential across any of the wires.
Tested the motor relays good. Verified they don't click when 4x4 switch is operated. Verified that, when the relays are manually triggered by grounding #85, the transfer case will shift into 4x4 with dash bulb illuminated and when the other relay is manually triggered the transfer case will go back to 2wd.
Replaced GEM module to no effect, no corrosion noted.
Verified continuity of #85 wires from relay back to GEM, brown with white and blue with orange.
Possibly related: overhead display gone dark (but it was already dim)
What to do next?
Submitted: 4 months ago.
Category: Ford
Expert:  HDGENE replied 4 months ago.

Hello, so you can make it shift into*****by grounding the relays, but otherwise it is stuck in 4x4 high?

Customer: replied 4 months ago.
No, the opposite. It's stuck in 2wd unless i ground a relay to shift to 4wd. It's currently in 2wd
Expert:  HDGENE replied 4 months ago.

Ok so both relays have 2 sources of power, just missing the ground circuit to apply the relay correct?The transfer case motor wont operate unless you ground it?

Customer: replied 4 months ago.
Ok so both relays have 2 sources of power - - - - I'm not sure what this means, they each are getting power.
just missing the ground circuit to apply the relay correct? - - - - This seems to be the case, yes
The transfer case motor wont operate unless you ground it? - - - - Yes
Expert:  HDGENE replied 4 months ago.

The GEM module grounds the circuit for the 4x4 operation. So if you havent run a diagnostic check for codes of the GEM module.This is what you would need to do at this point. Being able to see if the GEM module being used is working properly, not setting any fault codes. and looking at the input from the 4x4 switch will need to be checked to see what is missing in order for the GEM module to complete the circuit and actuate the Electonic shift on the fly system

Customer: replied 4 months ago.
How is this step done? Using a standard code reader or some special ford computer?
Remember I've already tried changing out the GEM.
Customer: replied 4 months ago.
What preconditions does the GEM require before it will command the shift to 4wd? Anything more to check on that front?
Do you know the location for the GEM ground to chassis?
Expert:  HDGENE replied 4 months ago.

A higher end scan tool or dealer scan tool. Not a conventional code reader. The GEM grounds the circuit internally to the module.

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 HIGH, 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 HIGH which is 4X4, and one for 4X4 LOW which is LOW RANGE (in 4X4 LOW both the lamps are on). Shifts into 4X4 HIGH can be made at any speed. When shifting into 4X4 HIGH 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 generic electronic module (GEM) 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 GEM 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 HIGH, 4X4 LOW, and 2WD range positions.

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

The GEM accomplishes shifts by interpreting inputs from:

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

Based on these inputs, the GEM controls the shifts into 2WD, 4X4 HIGH, 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 HIGH or 4X4 LOW position.

Expert:  HDGENE replied 4 months ago.

circuit

Customer: replied 4 months ago.
I'll get back to you when I get a code reader
Expert:  HDGENE replied 4 months ago.

Very good, let me know what you find and if you need more help

Expert:  HDGENE replied 4 months ago.

Hello, do you need more help with this concern?

Expert:  HDGENE replied 4 months ago.

If you need more help let me know. If I was helpful, please leave a positive rating.

Customer: replied 4 months ago.
I need more time to get the tool to continue the process.
Expert:  HDGENE replied 4 months ago.

Ok, Just checking in, been a few days since ive heard anything back.

Customer: replied 4 months ago.
I got a non-clone elm327 scanner with usb interface. What laptop software would be best to pair with this to read the GEM code?
Expert:  HDGENE replied 4 months ago.

I have no idea, that is an aftermarket scan tool setup, im used to using the dealer or OEM style equipment

Customer: replied 3 months ago.
OK, progress made on the electronic front.
The GEM stored codes are B1352 p1867 p1828 p1820 p1812 b1302 c1125 b1450
A GEM self test procedure results in the following: B1352 p1867 c1446 b1575 b1462
Expert:  HDGENE replied 3 months ago.

Ok, quite a few different codes for clockwise and counterclockwise relay coil circuits and the 4x4 switch. Does the scan tool you are using allow for live input? Can you see the 4x4 mode switch change from 2wd to 4x4 hi or low when moved?

Customer: replied 3 months ago.
I think it will do live input for these things:
transfer case shift relay [l2h] counterclockwise
clockwise relay control
4wd high indicator ledand will read these things:
2wd solenoid status
4wd high indicator lamp
4wd switch status
four wheel drive low warning indicator
4wd solenoid status
currently open contact plates
clockwise shift motor driver short to ground
counterclockwise shift motor driver short to ground
4wd low indicator status
Expert:  HDGENE replied 3 months ago.

Ok, clear the codes, look at the data input, see if the 4x4 switch indicates mode change

Customer: replied 3 months ago.
clear codes - that's understood
What does the rest mean - turn the truck 4x4 switch from 2x to 4xhi and see if the light illuminates?
Expert:  HDGENE replied 3 months ago.

Monitor the 4x4 switch input with the scan tool it set a code for the switch, need to see if the gem module is getitng an input from the used switch to change from 2wd to 4x4 high and low, if it is being commanded to change states.

Customer: replied 3 months ago.
The code reader is acting up and I've got weekend plans so it will be a few days until I respond to you. I'm really having trouble understanding your sentences. I think your last instruction is to move the trucks 4x4 switch to various positions and see if the "4wd switch status" code reading changes correspondingly - correct?
Expert:  HDGENE replied 3 months ago.

The GEM module has to see the 4x4 control switch change from*****to*****when you turn the switch. If the GEM module doesnt see the switch input status change it wont command 4x4. The scan tool live data will show what position the switch is turned to.

Expert:  HDGENE replied 3 months ago.

It will say 2wheel drive, 4x4 high, 4x4 low on the scan tool when turned to those positions if working correctly.

Expert:  HDGENE replied 3 months ago.

Do you understand what im trying to explain?

Customer: replied 3 months ago.
I think you're confirming the interpretation I gave, maybe you're not sure that "4wd switch status" is the appropriate data?
Expert:  HDGENE replied 3 months ago.

I dont follow you,one of the codes is for the 4x4 switch input.

Customer: replied 3 months ago.
simply resetting the GEM codes has resulted in the system working just fine. Is that how the computer is supposed to work? What hell awaits me down the road?
Expert:  HDGENE replied 3 months ago.

Being that you had other fault codes stored, you will need to see what codes reset if any, you changed parts along the way. So you may have fixed the concern. Time will tell for sure.

Expert:  HDGENE replied 3 months ago.

If you need more help let me know. If I was helpful, please leave a positive rating.

Customer: replied 3 months ago.
certain codes prevent operation and will not automatic reset when the fault goes away unless the computer is forced to clear them?
Expert:  HDGENE replied 3 months ago.

That is correct.

Customer: replied 3 months ago.
If I had disconnected the battery and grounded power, would that have cleared the GEM codes?
Expert:  HDGENE replied 3 months ago.

Not typically, the body control module has capaicators inside to keep alive and hold codes, some modules have to be cleared with a scan tool.

Expert:  HDGENE replied 3 months ago.

Do you need more help with this concern?