Operation CHARM: Car repair manuals for everyone.
Home >> Ford >> 2011 >> Explorer AWD V6-3.5L >> Repair and Diagnosis >> Transmission and Drivetrain >> Transfer Case >> Description and Operation >> Four Wheel Drive (4WD) Systems

Four Wheel Drive (4WD) Systems




Four Wheel Drive (4WD) Systems

Component Location










Overview

The AWD (All-Wheel Drive) system is always active and only requires the operator to select terrain. Torque from the engine is transferred through the transaxle to the PTU (Power Transfer Unit). The PTU (Power Transfer Unit) is a mechanical device attached to the transaxle. This torque is transferred through the driveshaft to the rear axle, which drives the rear halfshafts. The driver can optimize the AWD (All-Wheel Drive) system by setting the ATCM (All Terrain Control Module) switch for the correct terrain.

System Operation

System Diagram





Network Message Chart

Module Network Input Messages - AWD (All-Wheel Drive) System










All-Wheel Drive (AWD)

The vehicle is equipped with an AWD (All-Wheel Drive) system that continuously monitors vehicle conditions and automatically adjusts the power distribution between the front and rear wheels. The system is always active and only requires the operator to select terrain.

During normal operation, most of the torque is delivered to the front wheels. If wheel slip between the front and rear wheels is detected, or if the vehicle is under acceleration, the PCM (Powertrain Control Module) commands torque delivery to the rear wheels to prevent or control wheel slip. When the AWD (All-Wheel Drive) system is functioning properly, there should be no perceived speed difference between the front and rear axles when launching or driving the vehicle on any uniform surface. Traction should be similar to a part time 4WD (Four-Wheel Drive) system in 4H (4X4 HIGH), but have no binding in turns.

All AWD (All-Wheel Drive) control logic resides in the PCM (Powertrain Control Module). The PCM (Powertrain Control Module) continuously calculates if torque is required at the rear wheels and when torque is required, sends a low-current PWM (Pulse Width Modulated) signal to the AWD (All-Wheel Drive) relay module over a hard wired circuit. The AWD (All-Wheel Drive) relay module then outputs a high-current PWM (Pulse Width Modulated) signal which varies the current and duty cycle sent to the ATC (Active Torque Coupling) solenoid, which is located inside the rear axle.

The PWM (Pulse Width Modulated) current supplied to the ATC (Active Torque Coupling) solenoid increases as demand for rear wheel torque increases. The AWD (All-Wheel Drive) relay module returns a signal to the PCM (Powertrain Control Module) throughout AWD (All-Wheel Drive) operation over a hard-wired circuit to monitor system capabilities.

AWD (All-Wheel Drive) faults are indicated by the powertrain malfunction (wrench) warning indicator in the IPC (Instrument Panel Cluster) as well as the CHECK AWD (All-Wheel Drive) warning indicator in the message center.

A spare tire of a different size other than the tire provided should never be used. A dissimilar spare tire size (other than the spare tire provided) or major dissimilar tire sizes between the front and rear axles could cause the AWD (All-Wheel Drive) system to stop functioning correctly. If the incorrect spare tire or dissimilar tire sizes between the front and rear axles is installed, the AWD (All-Wheel Drive) system disables automatically and enters FWD (Front Wheel Drive) only mode to protect driveline components. This condition could be indicated by an AWD (All-Wheel Drive) OFF message in the message center. If there is an AWD (All-Wheel Drive) OFF message in the message center from using the spare tire, this message should disappear after reinstalling the repaired or replaced normal road tire and driving a short distance. It is recommended to reinstall the repaired or replaced road tire as soon as possible.

The PCM (Powertrain Control Module) also provides the ABS (Anti-Lock Brake System) with its current clutch duty cycle and determines whether or not the ABS (Anti-Lock Brake System) may take command of the clutch duty cycle.

The active, on-demand AWD (All-Wheel Drive) system uses data from other systems as inputs to the PCM (Powertrain Control Module). The PCM (Powertrain Control Module) uses the inputs to determine the appropriate duty cycle to send to the AWD (All-Wheel Drive) relay module and ATC (Active Torque Coupling) solenoid that delivers the desired torque to the rear wheels. Specific inputs to the PCM (Powertrain Control Module) are:

- ATCM (All Terrain Control Module) switch mode via the HS-CAN (High Speed Controller Area Network).

- Engine off status from the BCM (Body Control Module) via the HS-CAN (High Speed Controller Area Network).

- Steering wheel angle from the ABS (Anti-Lock Brake System) module via the HS-CAN (High Speed Controller Area Network)

- Yaw rate and Lateral acceleration from the RCM (Restraints Control Module) via the HS-CAN (High Speed Controller Area Network).

- Brake system status from the ABS (Anti-Lock Brake System) module via the HS-CAN (High Speed Controller Area Network).

- Wheel speed from all 4 wheels from the ABS (Anti-Lock Brake System) module via the HS-CAN (High Speed Controller Area Network).

- AWD (All-Wheel Drive) relay module diagnostic.

PCM (Powertrain Control Module) outputs are:

- PWM (Pulse Width Modulated) signal to the AWD (All-Wheel Drive) relay module to the ATC (Active Torque Coupling) solenoid for control of the solid-state clutch.

- Amount of torque transfer commanded signal to the ABS (Anti-Lock Brake System) module via the HS-CAN (High Speed Controller Area Network).

- AWD (All-Wheel Drive) system information to the IPC (Instrument Panel Cluster) via the HS-CAN (High Speed Controller Area Network).

- Returns terrain mode status and ready for change information to the ATCM (All Terrain Control Module) via the HS-CAN (High Speed Controller Area Network).

Terrain Management

Based on road conditions, the driver selects what mode the system is in by moving the ATCM (All Terrain Control Module) switch. The ATCM (All Terrain Control Module) sends information via the HS-CAN (High Speed Controller Area Network) to the:
- IPC (Instrument Panel Cluster).
- ABS (Anti-Lock Brake System) module.
- PCM (Powertrain Control Module).

The AWD (All-Wheel Drive) system adapts the responses of the vehicle's engine, transmission, suspension and stability control systems to match the demands of the terrain based on the ATCM (All Terrain Control Module) switch positions:

NOTE: Cruise control is available only in Normal and Snow modes.

NOTE: The Mud/Ruts and Sand modes are for off-road use only.

NOTE: Use Normal mode when towing a trailer.

- Normal - This mode is for on-road conditions. If not already active, Normal should be selected before driving on surfaces which are similar to a hard road surface. This mode should be selected once the need for a special mode has passed.

- Grass/Gravel/Snow - This mode should be used where a firm surface is covered with loose or slippery material. Surfaces covered in packed snow, ice, water, grass, gravel, or a thin coating of sand for example. For deep gravel, it is recommended that the Sand mode is selected. If the vehicle is unable to gain traction in deep snow, switching traction control off may help. Traction control should be switched on again as soon as the difficulty is overcome.

- Sand - This mode should be used for soft dry sand, or deep gravel terrain. If the sand to be crossed is damp/wet, and sufficiently deep enough to cause the wheels to sink into the surface, the Mud/Ruts mode should be selected.

- Mud/Ruts - This mode should be used for muddy, rutted, soft, or uneven terrain.

If the terrain management system becomes inoperable due to a system malfunction, all of the mode indicators on the control turns off and the message center displays one of the these messages:

- TERRAIN MANAGEMENT SYSTEM FAULT: If this message is displayed, cycling the key may clear the fault.

- MODE CHANGE NOT ACCEPTED, RETRY: If this message is displayed, a vehicle system cannot support a mode change at the time of driver request. Try the mode change again.

Heat Protection Mode

The AWD (All-Wheel Drive) system utilizes a heat protection mode to protect the PTU (Power Transfer Unit) and the ATC (Active Torque Coupling) solenoid from damage due to heat build up caused by clutch slippage while driving in extremely slippery road conditions. If the AWD (All-Wheel Drive) system detects an overheat condition, it increases the duty cycle to keep the clutches from slipping. If the heat in the system continues to rise, the AWD (All-Wheel Drive) relay module disables the ATC (Active Torque Coupling) solenoid. This condition may be indicated by an AWD (All-Wheel Drive) OFF message in the message center. Allow the system to cool down at least 10 minutes with the ignition ON (RUN). For concerns with the PTU (Power Transfer Unit), REFER to Symptom Chart: Power Transfer Unit (PTU) Transfer Case - Power Transfer Unit (PTU).

Component Description

Active Torque Coupling (ATC) Solenoid

The ATC (Active Torque Coupling) is part of the rear differential. The ATC (Active Torque Coupling) solenoid is not repairable. If a new component is required, the ATC (Active Torque Coupling) is installed new as an assembly with the rear axle. REFER to Axle Assembly Service and Repair.

Powertrain Control Module (PCM)

The PCM (Powertrain Control Module) controls the AWD (All-Wheel Drive) system based upon multiple inputs received via HS-CAN (High Speed Controller Area Network).

All-Wheel Drive (AWD) Relay Module

The AWD (All-Wheel Drive) relay module receives and returns information between the PCM (Powertrain Control Module) and the ATC (Active Torque Coupling) over hard wired circuits.

All Terrain Control Module (ATCM)

The ATCM (All Terrain Control Module) sends the driver selected rotary switch mode via the HS-CAN (High Speed Controller Area Network) to multiple systems.
pro multis · About Operation CHARM