Trunk / Liftgate: Description and Operation

Fig.8 Liftgate Control Module:

POWER LIFTGATE MODULE
Vehicles equipped with a Power Liftgate (PLG) utilize a PLG control module. This module is located on the vehicles left side D-pillar just below the motor assembly and contains a microprocessor, which is used to communicate to the vehicles body control module. The PLG control module receives and monitors logic inputs from all the PLG system switches except for the outside handle switch. This module also contains the software technology to detect liftgate obstructions and stop and/or reverse the door accordingly.

The PLG control module contains the electronic circuitry and software used to control the sequence of events for the PLG system. This module communicates on the PCI bus circuit with the vehicles body control module to monitor many different inputs and outputs such as door lock status, transmission gear selector position and vehicle speed. Refer to PLG system operation for more information.

POWER LIFTGATE SYSTEM

Fig.1 Power Liftgate Introduction:

Fig.2 Key Fob:

Some vehicles are equipped with an automatic opening and closing power liftgate system. This power liftgate system is a complex system consisting of many components. Some of these components are the liftgate gear motor assembly, latch assembly, lift gear and rod, liftgate control module, chime/thermistor, full open switch, engage actuator, pinch sensor, liftgate handle switch, overhead console switch, key fob switches, pawl switch and ratchet switch.

The power liftgate system has its own door control module, located on the vehicles left body D-pillar behind the trim panel. (Refer to ELECTRONIC CONTROL MODULES/DOOR CONTROL MODULE - DESCRIPTION) The power liftgate gear motor assembly is located just above the control module. The latch assembly is located in the bottom center of the power liftgate, below the exterior liftgate handle switch. The power liftgate full open switch, engage actuator, lift gear and rod are part of the liftgate gear motor assembly. The pawl and ratchet switches are part of the latch assembly. The pinch sensor or sensors are located along the right and left sides of the power liftgate, just above the body line. The liftgate handle switch is an power release switch and is located in the rear light bar assembly, just above the license plate. The overhead console switch is an power open and close command switch located in the vehicles overhead console.

Fig.3 Liftgate Fuse Location:

Safety is of the utmost concern with the power liftgate system. Software technology has enabled the power liftgate control module to detect resistance to liftgate travel, which allows the power liftgate to stop and reverse direction anytime an obstruction is felt or any of the command switches are operated (only in closing direction). Battery voltage is supplied to the power liftgate system through a 40 amp fuse, located in the Intelligent Power Module (IPM) assembly. In the unlikely event that the power liftgate system develops a fault the power liftgate can still be operated manually with a key, just like a standard manual liftgate.

The power liftgate control module communicates on the J1850 Programmable Communication Interface (PCI) Bus Circuit. Therefore, the power liftgate control module can generate and store its own Diagnostic Trouble Codes (DTC). The vehicles Body Control Module (BCM) receives and supplies messages to the power liftgate control module via the PCI bus circuit. A diagnostic scan tool, such as the DRB III is used to read and troubleshoot these Diagnostic Trouble Codes (DTC). Refer to the Body Diagnostic for a complete list of diagnostic routines.

For additional information refer to Power Liftgate Operation. For a complete system wiring schematic refer to Wiring Diagrams. For system operation instructions refer to the vehicles owner manual.

Refer to the Body for additional information on liftgate components such as the prop rods, hinges, door alignment and striker alignment.

WARNING: BE CERTAIN TO READ ALL WARNINGS AND CAUTIONS (NOTED BELOW) IN POWER LIFTGATE SYSTEM OPERATION BEFORE ATTEMPTING ANY SERVICE OF THE POWER LIFTGATE SYSTEM OR COMPONENTS.

With the push of a power liftgate open/close command switch (key fob or overhead console mounted) a signal is sent out on the J1850 PCI Data Bus circuit. This signal is detected at the body control module (BCM). The BCM then sends a signal out on the J1850 PCI Data Bus circuit to the power liftgate module. The power liftgate module then signals the power liftgate motor to start an open or close cycle, depending on what position the liftgate is in open or closed.

During a liftgate open or close cycle, if the power liftgate module detects sufficient resistance to liftgate travel, such as an obstruction in the liftgates path, the power liftgate control module will immediately stop the liftgate movement and reverse travel to the fill open or closed position. The ability for the power liftgate module to detect resistance to liftgate travel is accomplished by hall effect sensors, drive motor speed and pinch sensors (tape switches).

The power liftgate control module has the ability to learn. Anytime the liftgate is opened or closed using the power liftgate system the module learns from its cycle. If a replacement power liftgate component is installed or a liftgate adjustment is made, the module will relearn the effort and/or time required to open or close the door. This learn cycle can be performed with a Diagnostic Scan Tool, such as the DRB III or with a complete cycle of the liftgate, using any one of the command switches. Refer to Standard Procedures for detailed instructions.

The power liftgate system is designed with a number of system inhibitors. These inhibitors are necessary for safety and/or feasibility of the power liftgate system. Refer to power liftgate system inhibitors noted below:

Power Liftgate System Inhibitors
- The Power Liftgate may not operate in extreme temperatures. These extreme temperatures will be approximately 12 °F (-24.4 °C) on the low side and 143 °F (61.6 °C) for the high side. A chime/thermister assembly in the rear light bar assembly monitors the outside temperature.
- The vehicles transmission must be in park or neutral for the power liftgate to start a cycle.
- If multiple obstacles are detected during the same power open or close cycle the liftgate goes into manual operation.
- If severe Diagnostic Trouble Codes (DTC) are stored in the power liftgate control module.

Fig.4 Pinch Sensor Location:

PINCH SENSOR
Vehicles equipped with a power liftgate utilize two pinch sensors, one is located on each side of the liftgate. These sensors look like weather-strips, however they consist of pieces of electrically conductive rubber (tapeswitch), wires, resistor, double sided tape, and a plastic carrier. They are used to indicate an obstruction during a power close cycle.

During a power liftgate close cycle, if either of the two conductive rubber strips (tapeswitch) of the pinch sensor come in contact with an obstacle, the pinch sensor circuit is completed. This tells the power liftgate control module that a obstruction is felt. The control module will stop the liftgate immediately and return it to the full open position.

Fig.5 Full Open Switch Location:

FULL OPEN SWITCH
Vehicles equipped with a power liftgate utilize a full open switch. This switch is located on the gear motor housing and is used to signal the power liftgate module when the liftgate is in the full open position. Two wires are used from the full open switch contacts to the gear motor assemblies main electrical connector.

The full open switch is a serviceable component. Consult your Mopar parts catalog for a specific part number.

When the power liftgate reaches the full open position, the gear motor housing mounted full open switch electrical contacts come in contact with each other. This sends a ground signal to the power liftgate control module, telling the module that the liftgate has reached the full open position.

Fig.6 Power Liftgate Components:

LIFTGATE MOTOR
Vehicles equipped with a power liftgate, utilize a liftgate gear motor assembly. The gear motor assembly consists of a DC motor, hall effect sensor, engage actuator, full open switch, lift gear, aluminum housing, drive gears and wire harness. The gears and motor portion of the assembly provides the power and torque required to open or close the liftgate under the worst case conditions. The hall effect sensor is used to provide the liftgate control module with a speed reading, which is used to monitor the resistance of liftgate travel. This speed reading also allows the power liftgate control module to detect obstructions and move the liftgate accordingly. The engage actuator is used to toggle between power open/close mode and full manual mode when desired. The full open switch is used to let the power liftgate control module know when the liftgate is approaching the full open position.

Serviceable components of the power liftgate gear motor assembly are the complete gear motor assembly, motor and wire harness, lift gear and control rod, engage actuator, full open switch and the transverse bracket. Refer to additional information for more component details.

With the push of a power liftgate command switch (liftgate closed), the power liftgate control module will signal the latch assembly to release the door from its primary closed and latched position to the released and movable position. The liftgate motor mounted, engage actuator then engages the liftgate motor assembly, which moves the liftgate into the open position. The liftgate motor provides the torque and power to move the door to its full open or closed position (Refer to POWER DOORS - OPERATION) for additional information.

Fig.7 Liftgate Gear Motor Assembly:

ENGAGE ACTUATOR
Vehicles equipped with a power liftgate utilize a power liftgate engage actuator. The 12 volt engage actuator provides the engagement and disengagement of the liftgate gear motor to the lift gear by way of an over center link, activated by a lever.

The engage actuator is a serviceable component and cannot be repaired, if found to be faulty it must be replaced.

The engage actuators normal position is disengaged. When a power liftgate open or close command is generated from any of the command switches, the power liftgate control module signals the engage actuator to move its lever to the engaged position. This engages the gear motor to the lift gear, so when the motor turns the lift gate moves upward or downwards depending on its current position.

During a manual liftgate open or close cycle the engage actuator is disengaged, allowing unrestricted liftgate movement.

Fig.9 Liftgate Gear Motor Assembly:

TRANSVERSE BRACKET
Vehicles equipped with a power liftgate utilize a transverse bracket. This bracket is not different than any other metal bracket which is used to support and secure the power liftgate gear motor assembly to the vehicles left rear body D-pillar.

The transverse bracket is a serviceable power liftgate component. Consult your Mopar(TM) parts catalog for a specific part number.

The power liftgate transverse bracket supports the gear motor assembly by supplying an additional attachment point. Located on the leading edge of the gear motor assembly, one end of the transverse bracket attaches to the motor assembly the other to the leading edge of the vehicles D-pillar.

Fig.9 Liftgate Gear Motor Assembly:

LIFT GEAR & LINK ROD
Vehicles equipped with a power liftgate utilize a lift gear and rod assembly. This lift gear and rod assembly are located in the left rear of the vehicle and are visible without removing the D-pillar trim. The lift gear provides the leverage to move the liftgate from the closed to the open position. The lift gear attaches to a bearing on the gear motor assembly with four bolts. On the outboard side of the lift gear are rivited on teeth, which mesh with the gear motor assembly drive gears during a open or close operation. The rod assembly is a steel shaft, equipped with two spherical rod ends which attaches the lift gear to the liftgate.

The lift gear and rod assembly are serviceable components. Consult your Mopar(TM) parts catalog for a part number.

One end of the rod assembly is attached to the liftgate, the other attached to the lift gear. When the lift gear is driven by the gear motor assembly the liftgate is moved to the open or closed position.

Fig.12 Power Latch Orientation:

LATCH
Vehicles equipped with a power liftgate, utilize a power cinch/release latch. This latch performs the same features as a manual liftgate latch as well as the power cinch and/or release capability. A second type of power latch can also be found on some RS models, this latch is designed to perform a power release only. The power cinch and release capability is accomplished by an actuator mounted to the leading edge of the latch assembly. The latch is located in the lower center of the liftgate assembly and contains integral pawl and ratchet switches. The ratchet switch acts as a liftgate ajar switch.

The power latch assembly can be serviced as a complete assembly, latch without actuator or just the actuator. Consult your Mopar parts catalog for specific part numbers.

On the power cinch/release latch, the latch mounted actuator provides the torque required to close the power liftgate from the secondary to the primary closed and latched position. On the power cinch/release latch and the power release only latch, the actuator releases the liftgate from the primary closed and latched position to the fully unlatched and movable position.

Fig.13 Power Latch Orientation:

LATCH ACTUATOR
Vehicles equipped with a power liftgate utilize a power cinch latch or power release latch. The power cinch and/or power release is made possible by a latch actuator attached to the leading edge of the power latch assembly. This 12 volt latch actuator contains a small drive gear that meshes with the latch assemblies internal gears to perform the power cinch close/power release operations. Refer to the Latch assembly for more information.

The power cinch/release actuator is serviceable component. Consult your Mopar(TM0 parts catalog for specific part numbers.

During a power close cycle, the power cinch actuator provides the torque required to close the power liftgate from the secondary to the primary closed and latched position. During a power open cycle, the power release actuator releases the liftgate from the primary closed and latched position to the fully unlatched and movable position.

EXTERIOR HANDLE SWITCH
Vehicles equipped with a power liftgate or power locks utilize a exterior handle switch. The exterior handle switch is a electronic release switch mounted to the rear license plate lamp housing assembly, located just above the license plate. This switch controls the power liftgate release function and is also capable of reversing the power liftgate when it is in motion. A full power open cycle cannot be performed using this switch, only one of the power open command switches (key fob and overhead console mounted) can be used to perform a full power open cycle.

The exterior handle switch is a serviceable component. Consult your MoparTM parts catalog for a specific part number.

When the exterior handle switch is depressed, with the liftgate in the closed position. A message is sent to the Body Control Module (BCM). The Body Control Module then sends a signal to the power liftgate control module via the J1850 PCI data bus circuit. The power liftgate control module then sends a signal to the power latch mounted actuator, which moves the liftgate from the primary closed and latched position to the open and movable position. If the liftgate is not pulled open once the latch releases within a few seconds, the latch will cinch closed again.

Fig.14 Rear Light Bar:

CHIME/THERMISTOR
Vehicles equipped with a power liftgate utilize a chime/thermistor assembly. The chime/thermistor assembly is a small capacitor shaped electrical component mounted to the rear license plate lamp housing assembly, located just above the license plate. The chime portion of the assembly controls the audible chime sound heard at the rear of the vehicle when the power liftgate is in motion. The thermistor portion of the assembly is a temperature sensor, used by the power liftgate module.

The chime/thermistor assembly is a serviceable component. Consult your Mopar(TM) parts catalog for a specific part number.

The chime/thermistor assembly performs two different functions for the power liftgate system. First, the chime portion provides an audible chime sound which is controlled by the power liftgate module. The chime/thermistor assembly is hardwired to the power liftgate module. Second the thermistor provides a outside temperature reading by way of a resistance reading (ohms) supplied to the power liftgate module. As temperature increases the resistance reading (ohms) increases, as temperature decreases the resistance reading (ohms) decreases.