Description And Operation: Operation

The Power Transfer Unit (PTU) engages and disengages the propeller shaft as requested by the Drivetrain Control Module (DTCM). The DTCM receives information from other modules via CAN line, such as the gear engaged, engine load, vehicle speed, the drive mode requested by the operator, etc., to determine when to engage or disengage the propeller shaft on the basis of the most appropriate strategy. The DTCM controls an actuator installed on the PTU to transmit torque to the propeller shaft.

In "Auto" mode, (DTCM) controls the Power Transfer Unit (PTU) actuator so that when starting from a standstill or speeds close to 0 km/h (0 mph) the propeller shaft is always engaged. When the vehicle speed exceeds a set threshold, the engine load is not too high and the road conditions are ideal, the DTCM will command the PTU actuator to disengage the propeller shaft for the purposes of saving fuel. The conditions for which the DTCM re-engages the propeller shaft are, for example:

• If the road features irregular surfaces that compromises the dynamics/safety of the car.
• If the car speed returns to close to 0 km/h (0 mph).

The propeller shaft is disengaged only if the Select Terrain selector is in AUTO mode and only at a specific speeds in order not to compromise driving safety.

In the case of system or selector faults, the mode change option will be automatically disabled. The system will automatically set itself to "Auto" mode. The DTCM has the capability of storing Diagnostic Trouble Codes (DTCs) that can be read using an appropriate diagnostic scan tool to aid in diagnosing the system.

The vehicle operator can select up to five operating strategies based on surface conditions.

PTU modes: 

• AUTO (Automatic): the 4WD mode with continuous and automatic operation can be used while driving on road and off-road. This mode balances traction improving maneuvering and acceleration when compared to a 2WD vehicle. This mode also reduces fuel consumption, since it disconnects the propeller shaft when 4WD is not necessary.
• SNOW: this mode can achieve more stability on slippery or snow-covered grounds. To be used for driving on-road and off-road in the case of grounds with poor grip, such as roads covered by snow. In SNOW mode, depending on the operating conditions, the transmission may engage 2nd gear (rather than 1st) when setting off, in order to minimize wheel slipping.
• SAND: off-road driving mode to be used on grounds with poor grip, such as sand. The transmission is boosted for maximum traction.
• MUD : off-road driving mode for surfaces with poor grip, such as mud-covered grounds or wet grass.
• ROCK: This mode is only available for vehicles equipped with the 4WD LOW range. Adjustment based on traction with boosted steering capacity, for use on off-road surfaces with good grip. This guarantees the best "off-road" performance. This mode is to be used for obstacles to tackle at low speed, such as large rocks, deep cracks, etc.

Four-Wheel-Drive activation: 

• 4WD LOCK (available with manual gearbox and automatic transmission): deactivates the function for disconnecting the propeller shaft, guaranteeing the immediate availability of the torque to the rear coupling. This function can be selected in AUTO mode and is automatic in the other driving modes.
• 4WD LOW (available for Trailhawk versions with automatic transmission): it enhances the "off-road" performance of the vehicle in all driving modes. Low range is achieved by launching the vehicle with 1st gear in the transmission, versus the normal operating strategy of launching in 2nd gear. The PTU is a single range unit, with no internal gear reduction.