The 4WD in my 1998 Ford Explorer XLT stays engaged. Luckily, it's in 4H as opposed to 4L. I can tell because the ride is very heavy in the front and there is additional vibration. When I switch from 2WD to 4H, there is absolutely no difference in drive. The only difference is handling in that turning while it is in 4H isn't as sharp as in 2WD. I'm thinking that only one hub is locked in maybe, as opposed to a transfer case problem.

Any thoughts? What is the best way to diagnose the real problem? I know for a fact that at least one front wheel turns in 2WD. I went to our local e-check emissions branch and they couldn't run the truck on the rear rollers because a front wheel was locked in.

Again, what is the best way to diagnose the problem?

 

I thought that '98 and newer didn't have any kind of disconnect in the front axle at all; the front axle is a "live" axle. Maybe it was '99 and up. If it has a disconnect, it's vacuum actuated in the differential. And I believe that style leaves one axle permanantly connected to the wheel.

 

Here is a copy and paste that was sent to me:


The A4WD system is an electronic shift 4x4 system that allows the operator to choose between three different 4x4 modes. The operator can switch between A4WD and 4WD HIGH modes at any speed. To engage or disengage LOW range, the vehicle speed must be less than 5 km/h, the brake depressed, and the transmission must be in NEUTRAL.

The front/rear driveshaft speed sensors (Hall effect) are mounted to the transfer case and detect the speed of the front and rear driveshafts. This input is used by the generic electronic module (GEM) primarily to control A4WD operation.

The throttle position output signal is provided to the GEM from the powertrain control module (PCM). This signal is used by the GEM in controlling the A4WD clutch.

The shift motor sense plate, an integral part of the electric shift motor, informs the GEM to the position of the transfer case.

The digital TR sensors are located on the LH side of the transmission; these sensors inform the GEM when the transmission is in the neutral position.

The electric shift motor is mounted externally at the rear of the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the A4WD, 4HIGH, and LOW range positions.

The 4x4 shift motor uses a module containing two relays which, under the control of the GEM, shifts the transfer case shift motor between A4WD, 4HIGH, and 4LOW modes.

The solid state clutch relay is used to activate the A4WD clutch within the transfer case.

System Function

Hall effect sensor monitors input and output shaft speed.

In the A4WD (C-Trac) system, the GEM varies the torque sent to the front driveline by controlling the transfer case clutch. At rest and under cruising conditions, the GEM activates the transfer case clutch a minimum duty cycle (percentage of time the clutch is turned on), which allows for the slight difference between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. Under any of the following conditions, the GEM will increase the duty cycle in order to prevent or control slip:

Slip is detected (by using the Hall Effect Sensors)
Heavy acceleration.
Very light or zero throttle at speeds above 25 km/h (40 mph)
Feature inputs:

4WD mode switch.
Digital TR sensor.
Vehicle speed signal (transmitted from the ABS module).
Front/rear driveshaft speed sensors.
Throttle position information from the PCM.
Contact plate position inputs A, B, C, D.
Feature outputs:

Solid state clutch relay (pulse width modulated signal: grounded when relay is on, battery potential when relay is off).
A4WD indicator (ground when activated, open circuit when deactivated).
Shifts between A4WD and 4x4 HIGH can be made at any 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.
Hall effect sensors.
Contact plate position inputs A, B, C, D.
Feature outputs:

4x4 shift motor relay outputs.
Solid state clutch relay (pulse width modulated signal; grounded when relay is on, battery potential when relay is off).
4x4 HIGH cluster indicator (ground when activated, open circuit when deactivated).
When shifting into or out of LOW range, the GEM requires that the vehicle speed is less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

Feature inputs:

4WD mode switch.
Contact plate position inputs A, B, C, D.
Vehicle speed signal (transmitted from ABS module).
Brake input (battery voltage when brake is depressed, open circuit when not activated).
Digital TR sensor (ground when transmission is in NEUTRAL, open circuit otherwise).
Start/clutch depressed input.
Feature outputs:

4x4 shift motor relay outputs.
Cluster indicators (ground when activated, open circuit when deactivated).
Solid state clutch relay (pulse width modulated signal; grounded when relay is on, battery potential when relay is off).






I would make sure you have the same size tires all around and check all fuses.Then I would suspect the the front/rear driveshaft speed sensors,but you have to take it to a dealer or someone with a special New Generation STAR (NGS) Tester.