This site had provided countless information to help me in the past, so I'm hoping someone can point me in the right direction. Its a long read, but I tried to approach this logically not off the cuff.

Vehicle 1997 F150 4X4 ESOF 5.4l H9 diff.

I know the front end of the 4X4 is working since the Hubs will engage when they should and disengage when they should, so I'm only referring to the process of the transfer case engagement which is where the problem is.

From what I have learned and gathered from this site and the troubleshooting manuals for this truck this is how I interpret the process:When mode is changed to 4H the appropriate resistance is changed and the Gem acts accordingly. The Gem sees the resistance indicating 4H and grounds the L2H Shift relay coil. Since the 2 wires going to the shift motor are grounded by default via the shift relay the energized L2H coil produces the 12v on one wire for the shift motor. As the shift motor reaches 4H it is providing feedback via 4 contact plates to indicate the position it achieved. This position via the 4 plates is returned to the Gem. The Gem then removes the ground from the shift relay to stop the shift motor at that position. The Gem then grounds the 4x4 light on the dash to indicate 4H.

Originally (last year) it would shift into 4H regardless of switch position. I unplugged the shift motor to prevent accidental 4H while driving. Now that hunting season is done I went back to troubleshooting. Currently, changing the switch position, I have no movement of the shift motor or relay clicks. Based on the wiring diagrams, I checked fuses 29 (5A), 13 (15A), 23 (10A) and under hood 17 (30A) all good via ohm check.

I have 12v at the shift relay (to the right of the instrument cluster) on pins 3 and 5 (12v supply to coils). Switch on the dash tested good.

MODE SWITCH RESISTANCE SPECIFICATIONS

Switch Position Ohms Test value

2H 3705-4095 3900

4H 1050-1150 1098

4L 340-380 363



I removed the Transfer case shift motor and bench checked the contact plates in 2H and 4H, checked good according to the chart listed in the troubleshooting manual.

4WD MODE SWITCH PID OUTPUT

CONTACT PLATE 2H 4H

PLATE_A CLOSED OPEN

PLATE_B OPEN CLOSED

PLATE_C CLOSED CLOSED

PLATE_D CLOSED OPEN



When returning to 2H, I had to find the sweet spot for correct plate readings. Installed back in the truck and tested, 1 click on the Shift relay then nothing. I'm back to where I started, no movement, no relay clicks.

So, my thought at this time is the shift motor contact plates are not correct, based on trouble finding the sweet spot to get the correct plate readings. I'm second guessing myself because if the plate contacts were correct, it should change to 4H when commanded. but is doesn't. Or is something else at fault that I'm overlooking?

Thanks
Aubrey

 

,,,

 

When you turn the vehicle on it does a self test
If the four-wheel drive esof system fails the self test it is disabled.

It sounds like it's failing the self-test and disabled by the gem. No lights no clicking.

This would probably happen if the motor wasn't working right and returning the position.... Or there is a open circuit .

Curious know how you know your hubs are engaging and disengaging when you don't have hubs . You have a front axle disconnect. It won't work either if system is disabled

The shift motors from the factory fail eventually. Very very common failure. There is a chance that is not what it is.... But when it's dead with no dash lights no relays clicking.... And the fuses are good..... It's worth the $100 to just change the motor and eliminate that in 10 minutes. Yeah you can dink around with it if you like..... For months trying to save that couple of dollars.

. The shift fork in the front end is also a failure that's going to happen eventually in old truck if you haven't replaced it. It's an easy cheap 1 hr replacement.

There is probably a code in the PCM. I think you can read those with forscan

 

Thanks for the reply,
Reference the front end, I'm stuck in the older days, incorrect terminology, the Solenoids activate and vacuum pulls the fork properly to engage the front axles.

When the key is turned to on, from what I can tell, goes through the normal process. I don't have Forscan, I'm just comparing it to my other 97 F150 I had. Maybe I should get Forscan to help. Light for 4X4 on the dash do flash when key is turned on, so other than verifying the bulb is good I'm not sure what self test is accomplished. If I understand correctly, the feedback from the motor would have to be correct for the Gem to perform the self test and without the correct reading the Gem would stop?
.
I thought of buying the shift motor, but I wanted to break this down and understand the process to be more certain of the failed part instead of the many people that just keep buying parts in hopes they find the correct one. I was confident that this forum would have contributors that have seen enough issues to either point me in the direction or point out that I'm way off base...

Thanks
Aubrey

 

Well the problem is when the system is disabled by the gem...it becomes very difficult to test via any schematic.

I think when the vehicle is started the test consists of checking circuits for continuity, and actually moving the shift motor. If something fails it disables everything from that point.

The easiest path forward to replace the shift motor because it takes 10 minutes and 3x 10 mm bolts. Hardest part is moving one wire to the new plug. You have to release the pin from the old plug and pull it out and then stick it into the new plug. Or you could cut and splice wires. If that wouldn't it well then you know it's a wiring problem or a GEM problem. You can check wiring for continuity... Pretty time consuming and troublesome.


There was more than one mode of failure with the shift motors. Some of them went over range too far when internal plastic stop wore and then it lost position. Those could actually be fixed with a hack. I know that didn't happen to mine because I took it apart and looked. My circuitry just ceased to function properly.