Ok I posted on here and a few of you said to test some thing before posting again so here is what i got and where I need input. This is on my 97 F150 XLT 4x4 with electronic shift.

My 4x4 High will no engage with selecting 4H with the electronic shifter. 2H and 4L will. I replaced the switch removed the TC motor to see if it actually is moving it. It does not. When you select 4H the relays clicks under the oval by the passenger side.

things I did:
-replaced the stock TC motor and it did the same so I took that back and put the stocker back on. I had the motor off the TC to see if it spins the rod that actually moves it in to the selected position.
-replaced the electronic switch, still doing the same thing.

-bench tested the switch to make sure it's not bad either. I get the specified ohm resistance reading for 2H,4H,4L as I was told to check.

-I moved the relays around under the oval to determine witch one is for the electronic shift, but they all made the clicking sound. It just clicks click clicks clicks when you select 4H. Light does not come on and the clicking just keeps going till you select out of 4H.


questions I have:
-Does the GEM see anything after the switch has it's selection made or does it go the Relay and then to the TC motor?
-how do I test he signal after it leaves the switch?
-hint on how I can check at the relay to see if the GEM is sending the right amount of voltage.
-what pins can I check on the wiring harnes on the TC motor to see if there is anything going to the TC motor. I would assume no voltage since it's not moving when a selection is made.
-it was mentioned there was a relay behind the dash, guidance on how to get to it the easiest would be appreciated too.


thanks for any help. I'm really hoping to get this fixed this week since the snow is coming.

Thanks,

 

The only diagram I have is for a 99, hopefully it's the same. It seems the GEM is the brain of the system. In my diagram it has a 4x4 "high range" indicator. Does this indicator light when you engage the 4x4 high? What I am trying to determine first is if the GEM and the electronics "thinks" it's in 4wd, but it's really not.

 

The light does not come on in the dash....only clicking sounds uder the oval. If I select 4L the light for 4x4 and low comes on.

I was told the Gem uses the same wiring for 2H and 4H and 4L so I almost want to rule the GEM out since it is sending signal.

From my searching, usually folks have issues with 4L, not 4H like me. The clicking sound, is that the relay being bad (I did switch them all, but figured I"d throw it out there) or would it do that if the volatge was not right (low or to high)?

Also, the vacum lines for 4x4 system, is there one for 4H and one for 4L? And if there is, would that cause my issue? I have'nt checked those lines since I would assume it's just one line for both and 4L engages fine all the time.

 

Here's some info I copied from the factory 99 disc.


«1999 F150/250 Table of Contents»
«Group 3: Powertrain»
«Section 308-07A: TRANSFER CASE — GENERAL INFORMATION»
«DESCRIPTION AND OPERATION»


Transfer Case — Electronic Shift on the Fly (ESOF) Operation

The electronic shift on the fly (ESOF) system is an electronic shift 4x4 system that allows the operator to choose between two different 4x4 modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal depressed, and the transmission must be in NEUTRAL.

The transfer case is equipped with an electromagnetic clutch which is located inside the case. This clutch is used to spin up the front driveline when shifting from 2WD to 4H mode at speed. When the control switch on the instrument panel is turned, the generic electronic module (GEM) recognizes that a shift has been requested and activates the electromagnetic clutch and the relays which power the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the GEM, power to the shift relays and motors will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle collar is engaged and the electromagnetic clutch is deactivated.

Shifts between 2WD and 4H can be made at any speed up to 88 km/h (55 mph). Listed below are the inputs and outputs needed by the GEM to execute a change between any of these modes.

Feature Inputs:

l 4WD mode switch (various resistances; go to Table 1).

l Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).

Feature Outputs:

l 4x4 shift motor relay outputs (go to Table 2).

l Transfer case clutch relay (grounded when relay is activated, open circuit when relay is deactivated).

l 4x2/4x4 vacuum solenoid (grounded when activated, open circuit when deactivated).

l Cluster indicators (ground when activated, open circuit when deactivated).

When shifting into or out of 4L, the GEM requires that the vehicle speed be less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

Feature Inputs:

l 4WD Mode Switch (various resistances; go to Table 1).

l Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open; go to Table 4).

l Output Speed Shaft (OSS) Sensor (Sinusoid Signal: 0.7V-20V, 2.2 Hz/mph).

l Brake Input (battery voltage when brake is depressed, open circuit when not activated).

l Transmission Range Sensor (grounded when transmission is in NEUTRAL, open circuit otherwise).

l Start/Clutch Depressed Input (go to Table 3).

Feature Outputs:

l 4x4 Shift Motor Relay Outputs (go to Table 2).

l 4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).

l Cluster Indicators (grounded when activated, open circuit when deactivated).

-------------------------------------------------------------------------------------


«1999 F150/250 Table of Contents»
«Group 3: Powertrain»
«Section 308-07A: TRANSFER CASE — GENERAL INFORMATION»
«DESCRIPTION AND OPERATION»


Transfer Case — Electronic Shift on the Fly (ESOF) Features

A rotary switch allows the vehicle operator to choose between 2WD, 4H, and 4L modes of 4x4 operation.

The generic electronic module (GEM) controls the operation of the 4x4 system.

The output shaft speed (OSS), mounted in the rear of the transfer case, informs the GEM of the vehicle speed.

The shift motor sense plate, an integral part of the electronic shift motor, informs the GEM to the positions of the transfer case (go to Table 4).

The transmission range sensor is located on the LH side of the transmission; this sensor informs the GEM when the transmission is in the NEUTRAL position.

The electronic shift motor, mounted externally at the rear of the transfer case, drives a rotary cam which moves the mode fork and range fork within the transfer case to select between the 2WD, 4H, and 4L positions.

The 4x4/4x2 vacuum solenoids are attached to the upper RH side of the engine compartment, and alternately route vacuum to the vacuum motor which engages/disengages the center axle disconnect collar in the front axle assembly.

The 4x4 shift motor relay is a module containing two relays. Under the control of the GEM, the 4x4 shift motor relay shifts the transfer case shift motor between the 2WD, 4H, and 4L modes.

The transfer case clutch relay is an electromechanical relay used to activate the transfer case clutch within the transfer case.

 

I appreciate the help....

I read over the info and trouble shooting you listed there, it mentions two relays for the shift motor relay...was there any input to where those are?

Also, I'm not a electrical person. but since the relay is clicking under the oval, does that suggest the GEM is sending a signal to it, or does the signal go from the switch to the relay then the GEM?

I'm hoping it's not the GEM, but to me since it switches from 2H to 4L it should'nt be the GEM.

Thoughts, suggestions?
Thanks

 

The Mode switch has three resistance values to tell the GEM directly what position the switch is in. The Gem grounds the transfer case electric clutch relay to activate the electric clutch coil in the transfer case. It also provides ground for the transfer case electronic shift relay module which depending on which position the GEM demands will power the shift motor. The Gem also determines the position of the shift motor via contact plates within the shift motor. The Gem also controls the two axle disconnect solenoids.

Hope this bit of info helps.

 

Here are the 4x4 tables referenced in a previous post above.
Looking at this makes me love that lever I have sticking out of the floorboard.

 

The resistance in the selections switch turned out ok....are you leading toward the GEM being the issue?

 

Here is something else I noticed today and it that fixed my issue this would be nice but I'm sure is not my luck:

tonight I looked at the vacume lines and noticed something strange and this might be my cause. There are 2 vacume hoses going from the front end light blue and red or orange that go behind the battery. There is also a black rubber hose (larger) that is plugged into the front end that runs along the vacume hoses....does that black hose lead to somewhere or is that just a breather hose? I was looking at it and it seemed to be cut, again that is if it's not a breather hose. Just seemed odd.

 

It sounds like the breather hose. You will have one on the rearend and the transfer case too.

 

figures....I was hoping that might be the issue.

Where is the second relays located, I found the one under the oval....the above info that was posted mentioned a second relay.

I'm leading toward the GEM since the relay is just clicking and no light comes on for 4H. Just weird how 2H and 4L works but no 4H.

I've never experienced a relays just keep clicking.

 

The transfer case clutch relay is located in a RPO relay block. This block is behind the dash on the passenger side, up high near the base of the windshield.

The transfer case shift relay module is also behind the dash up high, but more over in the center of the dash up high behind the radio area.

The GEM module is a fairly large box with three plugs going to it, and is mounted on the driver's side under the dash, close to the driver's side kick panel area.

 

The Gem module is physically attached and interfaced to the back side of the interior fuse box.

 

interesting...I'll have to see if I can pinpoint them down. I know one of them is right there when you remove the large oval cover on the passenger side dash. It's with a few other relay's and a large relay. When you remove it the clickign sound stops when you select 4H. I'm guessing that is the transfercase clutch relay.

Is there an easy way to determine with one is the transfer case shift relay? pull the radio to see it? Or can it be seen from the Oval area when the oval is removed? Whats the easiest way to see/ get to that relay?

Thanks again.

 

yea I know where the GEM is...I was thinking about taking it out and cleaning the contact and putting it back in to see if that helps.