Power Liftgate System Description

Liftgate Control Module 

The liftgate control module controls the liftgate motor, liftgate clutch, and liftgate latch based on various inputs. The liftgate control module also performs diagnostics on these inputs and outputs and will disable liftgate functionality and set DTCs should a fault be detected. The liftgate control module is secured to the motor assembly at the left rear of the vehicle. The module requires a liftgate position learn procedure be performed when replacing. This allows the module to learn the full open and full closed positions of the liftgate.

Instrument Panel Multifunction Switch 

The interior liftgate control switch has switch that is used to change the function of the liftgate system from either a power mode or a manual mode of operation. When the switch is placed in the Off position, the liftgate control module will suspend the function of the liftgate motor which means the liftgate must be pulled open or pushed closed.

The interior liftgate control switch has a push button switch to command the liftgate to power open and power close when selected in the power mode or to release the liftgate when in the manual mode. The liftgate control module monitors the voltage level on the open/close signal circuit, when the switch is not being pressed the voltage level is at the system voltage. When the switch is pressed a contact within the interior liftgate control switch closes providing a ground path for the signal circuit causing the voltage level to drop to near zero volts. The liftgate control module will detect the voltage drop and will then command the liftgate to open or close depending upon the current state of the liftgate at the time the switch is pressed.

Liftgate Motor Assembly 

The motor assembly is located at the left rear of the vehicle and contains the liftgate motor, liftgate clutch, hall effect sensor, and the open switch. The motor assembly also provides means to open the liftgate by way of a gear set. During operation, the liftgate motor drives the gear set that raises and lowers the liftgate through a strut rod connected to a lever which is part of the gear set. The liftgate control module applies voltage and provides ground to operate the liftgate motor and clutch. When liftgate operation is requested, the liftgate control module engages the clutch and begins driving the motor. If a fault were to occur that requires the disabling of liftgate functions, the liftgate control module would release the clutch, allowing manual operation of the liftgate. The liftgate control module determines the position of the liftgate based on the hall effect sensor and open switch. The liftgate control module applies voltage and provides a ground path to power the hall effect switch. As the liftgate is in motion, the hall effect switch rotates, alternately pulsing the applied voltage on each of the 2 hall effect signal circuits. The liftgate control module determines the position based on the number of hall pulses, or counts, received. When the liftgate is fully open, the open switch is closed. This provides an input to the liftgate control module to indicate the liftgate has reached its full open position.

Liftgate Latch 

The liftgate latch contains the cinch/release motor, as well as 3 liftgate switches. Each of the 3 switches contained within provide a discrete input to the liftgate control module. These switches act as a liftgate open switch, a liftgate ajar switch, and a cinch/release switch. The liftgate control module looks at these inputs to determine when the liftgate has cleared the latch during opening and to determine when the liftgate is seated in the latch during closing. When the liftgate open and ajar switches are seen to be closed, indicating a closed liftgate, the liftgate control module will command the cinch/release motor to cinch, pulling the liftgate tightly closed. When a liftgate open operation is requested, the cinch/release motor will release, allowing the liftgate to clear the latch and begin opening.

Liftgate Object Sensors 

On each side of the liftgate opening is an object detection sensor, these sensors are pressure sensitive touch tapes located along the edges of the liftgate. Either of these 2 sensors will disable liftgate closing or reverse an already in motion liftgate should an object come in contact with a sensor. If pressure is applied to either strip as the liftgate is closing, an input will be sent to the liftgate control module signifying that an object has been detected and the liftgate control module will command the liftgate motor to change direction and the liftgate will power open.

Liftgate Handle Switch 

Located in the liftgate handle is the liftgate handle switch. This switch provides a discrete input to the liftgate to indicate when a liftgate release operation is requested. Opening the liftgate using the handle will not cause the liftgate to automatically raise. Only the liftgate latch is released when using the handle.

Liftgate Close Switch 

Accessible only when the liftgate is open, the liftgate closed switch provides a discrete input to the liftgate control module to indicate when a liftgate close operation is requested.

Liftgate Ajar Indicator 

The driver information center located on the instrument cluster, illuminates the LIFT GATE AJAR indicator when the liftgate control module detects the liftgate latch ajar switch is closed to ground indicating the liftgate is open. The instrument cluster receives a serial data message from the liftgate control module indicating the liftgate ajar status. If this message is displayed and the vehicle speed is greater than 4.8 km/h (3 mph), a chime will sound.