Automatic Four Wheel Drive (A4WD)

DESCRIPTION
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 kph, the brake depressed, and the transmission must be in NEUTRAL.

OPERATION
In A4WD, the generic electronic module (GEM) varies the torque split between front and rear drivelines by controlling the transfer case clutch. Under most conditions, the GEM activates the transfer case clutch at a minimum duty cycle (percentage of time the clutch is turned on) which allows for a slight speed difference between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the GEM detects this slip condition, and the duty cycle to the transfer case clutch is increased until the speed difference between driveshafts is reduced. In this manner, the GEM can redirect 4 to 98% of engine torque to the front wheels when the rear wheels lose traction, yet still allow operation in the A4WD mode on dry pavement.

Feature inputs:
- 4WD mode switch.
- Transmission range (TR) or digital transmission range (DTR) sensor.
- Vehicle speed sensor (VSS) switch.
- Front/rear driveshaft speed sensors.
- 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).

SHIFTING BETWEEN A4WD AND 4X4 HIGH
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.
- 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).
- Cluster indicators (ground when activated, open circuit when deactivated).

SHIFTING INTO/OUT OF LOW RANGE
When shifting into or out of LOW range, the GEM requires that the vehicle speed is less than 5 kph, the brake is applied, and the transmission is in NEUTRAL.

Feature inputs:
- 4WD mode switch.
- Contact plate position inputs A, B. C, D.
- VSS sensor.
- Brake input (battery voltage when brake is depressed, open circuit when not activated).
- Transmission range (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).