4wd does not work
Electronic Shift On the Fly (ESOF) Operation
The 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 4WD HIGH mode at speed.
To engage or disengage LOW Range, the vehicle speed must be less than 5
kph, the brake 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 drive-line when shifting from 2WD to 4x4 High 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 main-shaft hub to the drive
sprocket. Finally, the front axle collar is engaged and the
electromagnetic clutch is deactivated.
Shift Between 2WD and 4x4 HIGH:
Shifts between 2WD and 4x4 HIGH can be made at speed. Listed below are
the inputs and outputs needed by the GEM to execute a change between
any of these modes.
Feature Inputs:
*4WD Mode Switch (Various resistances).
*Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open).
Feature Outputs:
*4x4 Shift Motor Relay Outputs
*Transfer Case Clutch Relay (grounded when relay is on, open circuit when relay is off).
*4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).
*Cluster Indicators (ground when activated, open circuit when deactivated).
Shifting Into/Out of 4WD LOW:
When shifting into or out of 4WD LOW, the GEM requires that the vehicle
speed be less than 5 kph, the brake is applied, and the transmission is
in NEUTRAL.
Feature Inputs:
*4WD Mode Switch (Various resistances).
*Contact Plate Position Inputs A, B, C, D (grounded when closed, open circuit when open).
*VSS Sensor (Sinusoid Signal: 0.7V-20V, 2.2 Hz/mph).
Brake Input (battery voltage when brake is depress, open circuit when not activated).
*Transmission Range Sensor (grounded when transmission is in NEUTRAL, open circuit otherwise).
8Start/Clutch Depressed Input
Feature Outputs:
*4x4 Shift Motor Relay Outputs
*4x2/4x4 Vacuum Solenoid (grounded when activated, open circuit when deactivated).
*Cluster Indicators (grounded when activated, open circuit when deactivated).
4WD Mode Switch
A rotary switch allows the vehicle operator to choose between 2WD, 4WD HIGH, and 4WD LOW modes of 4x4 operation.
GEM Module
The Generic Electronic Module (GEM) controls the operation of the 4x4 system
Vehicle Speed Sensor
The vehicle speed sensor (VSS), mounted in the rear of the transfer case, informs the GEM of the vehicle speed.
Transfer Case Shift Motor Sense Plates
The shift motor sense plate, an integral part of the electric shift motor, informs the GEM to the positions of the transfer case
Transmission Range Sensor
Located on the left side of the transmission, this sensor informs the GEM when the transmission is in the NEUTRAL position.
Electric Shift Motor
The electric 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, 4WD HIGH, and
4WD LOW positions.
4x4/4x2 Vacuum Solenoids
These two solenoids are attached to the upper RH side of the engine
compartment dash, and alternately route vacuum to the vacuum motor
which engages/disengages the center axle disconnect collar in the front
axle assembly.
4x4 Shift Motor Relay
A module containing two relays which under the control of the GEM,
shift the transfer case shift motor between the 2WD, 4WD HIGH, and 4WD
LOW modes.
Transfer Case Clutch Relay
An electromechanical relay is used to activate the transfer case clutch within the transfer case.
Good luck and hope this helps,but start with the simple and check the fuses and wire harness. Both white/light blue stripe wires should have 12V in run. The GEM will
ground the left side (closest to engine) solenoid to disengage the
front axle. It will ground the the right side solenoid (closest to
fender) to engage the front axle. If the GEM doesn't see Neutral it
will not let the truck come out of 4Lo. If the GEM had water leaking on
it it may well be the root of the problem. The shift motor only has
power when the GEM sends it a signal to move the shift lever. Once the
shift is completed the motor shuts off. There are 2 wires that control
the shift motor. A yellow and an orange. The GEM alternates between 12v
and Ground to these wires to control which way the motor turns. The GEM
uses the transfer case shift relay module to control the power to the
motor. There are contact plates inside the shift motor assembly that
indicate the position that the shift lever is in. This is what the GEM
used to know what the T-case is doing. Any one of these components can
fail.
The simple answer is yes, located off the shift motor there is a connector.
Thanks for trying to help Lake I have power on the relays but it doesn't go through to the transfer motor. I found a plug in between and have current flow but only if I jumper the relays. My 04 has no gem module and the pcm does everything it should but power up the 4X4 transfer case. I have power on the selector switch (new) power on relays and fueses. I can shift it easily if I take the motor off or jump the relay coil. My PCM never lights the lights on the switch and all the trouble shooting charts either talk about a unit with a seperate module or work of a secanorio where the lights come on at the switch. I am a retired mechanic and when I am lost it gets bad quick. thanks Lynn
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