4A and 4H Operation

4A turns on when you select EXCITE, NORMAL 4x4 AUTO or SLIPPERY. It provides electronically controlled four-wheel drive with power delivered to all four wheels, as required, for increased traction. 4A is calibrated in conjunction with Drive Mode. 4A in EXCITE is less aggressively tuned and is appropriate for dry road surfaces. 4A in NORMAL 4x4 AUTO is appropriate for all on-road driving conditions, such as dry road surfaces, wet pavement, light snow or gravel. 4A in SLIPPERY is more aggressively tuned and is appropriate for slippery surfaces, such as light snow or gravel.

4H turns on when you select DEEP CONDITIONS. It provides electronically locked four-wheel drive power to both the front and rear wheels for use in off-road or winter conditions such as deep snow, sand or mud. This mode is not for use on dry pavement.

In 4A:

• The ATCM sends a 4L mode status on the HS-CAN2 via the GWM to the TCCM on the FD-CAN (4x4_SW = 4WD_LOW).
• The TCCM outputs a 0% to 97% duty cycle to the clutch field coil (4WD_CLUTCH_OUTPUT # = x.xx%).
• In 4H, the TCCM outputs a constant 97% duty cycle to the clutch field coil.
• 4A or 4H is displayed in the message center.

In 4A, the TCCM continuously monitors conditions and driver input to send torque automatically to the front driveline by controlling the transfer case clutch, providing 4WD capability. The TCCM sends a duty cycle command to the transfer case clutch coil as a torque request based on combination of preemptive and wheel slip response algorithm. Preemptive response is based on steering wheel angle, vehicle speed, throttle positions and available powertrain torque. Wheel slip response is based on monitoring the average front and rear wheel speeds.

When 4WD is no longer needed (during cruising or steady state driving) system defaults back to RWD mode by setting the duty cycle output to 0.

TCCM increases the duty cycle to prevent or control slip under any of the following conditions:

• Slip is detected.
• Heavy acceleration (throttle position).
• Straight-ahead steering wheel angle.
• Slippery or Deep Conditions drive mode is selected.

TCCM decreases the duty cycle to prevent or reduce vehicle bind under any of the following conditions:

• Low speed.
• Low acceleration (throttle position).
• Tight turn steering wheel angle.
• Excite drive mode is selected.

The TCCM has a thermal hardware protection strategy which monitors the amount of energy going through the clutch. This strategy has 2 levels of protections:

• AUTOLOCK 

  - If the system is in 4A and TCCM detects driving conditions that require greater 4X4 performance, the TCCM temporarily turns on 4H from 4A after detecting driving condition and informs the customer via the message center indicating 4X4 TEMPORARILY LOCKED. The 4x4 system automatically returns to 4A after the system no longer detects these driving conditions and informs the customer via the message center indicating 4X4 RESTORED.

• POWERTRAIN TORQUE PROTECTION 

  - If the system is in 4A and TCCM detects excessive stress or high energy going through the clutch (clutch is slipping excessively while the system is commanding max clutch torque), clutch output will be turned off and message center indicates 4x4 TEMPORARILY DISABLED. When the system had the ability to cool off, 4x4 operation will be automatically restored.