Hello,

The dark blue wire powering the selector switch only has 5V. When watching a digastric video, it was indicated it should be closer to 12V. The volage does not change when the truck is running. Have verified that the ground is working. The light in the switch is working. The selector switch has the correct resistance for 2, 4H, & 4L.

I have read many post about the 4x4 not working and items to check out. I have verified that all fuses are working, The solenoids have power, The transfer motor does work when jumped to power.

Thanks for your help

-Mark

 

I’m not sure what you‘re asking

I don’t know if your four-wheel-drive system isn’t working, we don’t know if you have like vacuum issues, we don’t know if you’ve tried putting 12 V to the other side of your switch where you’re allegedly only seeing 5 volts and that fixes your “issue”





Maybe you should just start at the beginning

 

Whatever video you watched, it's wrong. That circuit is sourced from the internal 5 volt reference voltage in the GEM.

Back-probing at that DB wire, ignition in RUN, and rotating the switch through its positions should yield different voltages measured on that wire.

 

Took voltage readings as the selector switch has rotated. Voltage dropped consistent with the resistance in each switch location.. E=I*R

Haven't had time to do more than that this past week.

-Mark

 

Here is the link to the video showing the switch receiving over 11 volts.


-Mark

 

Pulled the vacuum hoses off the firewall solenoids. Both are receiving vacuum. 4wd has internal resistance of 64 ohms. 2wd has internal resistance of 71 ohms. Both solenoids are receiving power. In 2wd the ground is good. In 4wd the ground.is an open circuit.

This would indicate that relay directing the ground leg is not activating. Where is the relay?

Thanks.

-Mark

 

Let's back up a bit...

1. What is the operational symptom?
2. Have you scanned the GEM for any fault codes (you must use an appropriately capable scan tool or equivalent)?
3. Have you followed the diagnostic procedure in the factory service manual? If you don't have it or the schematic, I can post it.

Notes:
The vacuum solenoids on the firewall are triggered by internal circuitry in the GEM module. Probably switched by transistors, not relays.
Bless their hearts, Ford used dark blue wires for both the signal input and the signal ground wires between the GEM and the 4x4 selector switch. With power removed, one of those wires should show continuity to ground.
And, FWIW, the guy in the video made several mistakes regarding the pin configuration of the selector switch connector. The black wire is the ground for the backlight circuit. The two dark blue wires, pins 2 & 3 respectively, are the switch's output (input to the GEM module) and the signal return for the switch. Pin 2 has a pull-up resistor (unknown value) to the GEM's internal reference voltage supply. With the switch disconnected and measuring between pins 2 & 3, you should read that source's voltage.

 

Major symptom is that the the transfer case does not shift into 4x4, nor does the 4x4 indicator light up.. (I have applied power directly to the electric drive of the case and it does function.}

Current scanner is old and doesn't give any codes related to GEM module. Have ordered an USB interface reader that promises to give more than engine codes,

-Mark

 

With that early model truck, the scan tool has to be able to connect to the ISO 9141 bus, pin 7 of the DLC. Double-check your device's capability if it doesn't seem to read the GEM.

 

Received a Forscan reader yesterday. Got the following GEM codes:

P1820 Transfer case low to high shift relay coil circuit failure
P1828 Transfer case low to high shift relay coil circuit failure Cause? Open circuit between GEM & Transfer Case Shift Relay (CCW relay) -Short to GND between GEM & Transfer case Shift Relay (CCW relay)
P1824 4 Wheel Drive Clutch Relay circuit Failure
P1832 Transfer case 4wd Solenoid Circuit Failure
P1876 Transfer case 2wd Solenoid Circuit Open or Short to Ground.

Is CCW Relay part of the GEM module?

-Mark

 

Those codes would tend to indicate that those 5 relays/solenoids are all missing their supply voltage.

My Ford diagrams are in disagreement as to where they get their power so I'm operating under the assumption that they are either in error or have an omission (wouldn't be the first time I've found either). That said, check fuses F15 and F23 in the under dash fuse box. The schematics say F23, the diagnostic routine says to check fuse F15. I suspect at least one of them is not passing power when the ignition switch is in the RUN position.

 

Dash is completely torn apart around the steering wheel. Replaced the CCW relay that is buried in there, but it did not fix the issue. Crawled under the rig last week and hotwired the transfer case motor to put the case in 4 Low with the selector switch also in low. Started the truck up and discovered that I can now plow snow. While I have the dash apart I am going to relace all the bulbs in the instrument panel. Then I can contemplate about replacing the GEM module.

-Mark

 

Hi Mark, Did you get your 4 wheel drive issue fixed. I am having the exact same issue with my 1997. I have concluded it's the GEM. I will have the replacement this weekend. Will let you know if that fixes it.

 

The videos linked in this thread are good for diagnosing and fixing 4x4 issues

https://www.f150forum.com/f6/4x4-tra...-shift-565190/

 

Once I got the truck in 4x4 low so that i could plow snow, I stopped working on it. I will not be trying to fix it until it stops snowing for the season. Up here that usually means late April.

-Mark