Section 22 (Transfer Case - Diagnosis - New Venture 246): Operation
ATC control module is capable of engaging front axle while vehicle is in motion. It does this by applying pulse width modulated signal to electric motor to activate motor, which applies torque to front axle. This action is used to match speed of front and rear drive shafts. After control module senses proper speed, it then supplies a ground to front axle actuator to engage front axle. ATC control module will accept a mode shift only when engine is running and valid motor/encoder signal is present. A mode shift is any shift between 2H, 4H and AUTO. ATC control module will permit a range shift only if the following conditions are met within 30 seconds of request: engine is running, transmission is in Neutral, vehicle speed is less than 3 MPH and proper motor/encoder signal is present. A range shift is a shift between 2H, 4H, AUTO (high range) and 4L (low range). ATC control module will permit a range shift into or out of Neutral only if the following conditions are met: ignition is on, transmission is in Neutral and vehicle speed is zero.
4WD mode (4H or 4L) is accomplished by engaging front axle, applying pulse width modulated signal to electric motor to apply maximum torque (fully compressing transfer case clutch plates) to front axle, then removing ground circuit, which locks motor in position and stops pulse width modulation to motor. In AUTO mode, system should engage front axle, then monitor front and rear drive shaft speeds for any speed difference. See Fig 1 . When system senses rear wheel slip, or a difference in drive shaft speed between front and rear drive shafts, ATC control module will use pulse width modulation to drive electric motor. Motor transfers only required torque to front wheels to gain additional traction on slippery surfaces up to 75 MPH. There is no torque applied to front wheels until control module senses rear wheel slip.
Throttle anticipation, which is only operational in AUTO mode, occurs if vehicle speed is less than 5 MPH and accelerator is pressed quickly beyond a set point. System will automatically transfer a percentage of torque to front wheels to help prevent rear wheels from slipping, such as in a hard acceleration from a stopped position.