Principles of Operation
PRINCIPLES OF OPERATIONPower and Ground Requirements
The power requirements for the power liftgate (PLG) module are 4 fused battery supply circuits. The smart junction box (SJB) fuse 11 (5A) supplies battery logic power required for the software and internal switching operations. The motor and clutch power is supplied by bussed electric center (BEC) fuse 8 (30A). The ignition - start power is supplied by SJB fuse 20 (10A). The ignition - run power is supplied by SJB fuse 13 (10A).
Ground for the PLG module is a separate single connection. Some of the continuous inputs which are at a ground state when ON are also used for logic switching.
PLG Detent Switch, Forkbolt Primary Switch and Forkbolt Secondary Switch
Latch Switch States:
The PLG detent switch, forkbolt primary switch and forkbolt secondary switch provide inputs to the PLG module in order to determine liftgate latch position. The PLG module receives inputs from the PLG detent switch, forkbolt primary switch and forkbolt secondary switch in the following order during a close operation.
Unlatch Actuator
Power is supplied to the unlatch actuator by the PLG module when a valid open command is received. The actuator unlatches the liftgate similar to a manual activation of the door handle. The unlatch actuator is a bi-directional motor. Once the unlatch actuator releases the liftgate, the PLG module reverses current flow to the unlatch actuator in order to help the return spring push the latch mechanism back to the normal rest position.
Cinching Actuator
Power is supplied to the cinching actuator by the PLG module when the SECONDARY LATCH position is reached during a power close operation. When the actuator activates, it pulls the liftgate into the PRIMARY LATCH position. The PLG module removes power from the cinching actuator when the PRIMARY LATCH position is reached.
Position Sensor
The PLG module supplies a 5-volt reference voltage to the position sensor on a valid open command or anytime the liftgate is in the OPEN position (up to 6 hours). The PLG module constantly supplies the ground. The position sensor has 2 data lines that the PLG module monitors to determine the liftgate movement and position. The PLG module uses the liftgate position information to determine which direction to power the liftgate (OPEN or CLOSE) when a valid operation command is received. The movement is monitored to identify obstructions.
Drive Assembly Actuator Clutch
The drive assembly actuator clutch separates the drive assembly actuator motor from the liftgate drive gear. This allows manual opening and closing of the liftgate without driving the motor. The PLG module supplies power to the drive assembly actuator clutch for any valid OPEN/CLOSE operation. The clutch connects the drive assembly actuator motor to the drive gear, allowing the motor to turn the gear and open or close the liftgate.
Drive Assembly Actuator Motor
The drive assembly actuator motor is a reversible pulse width modulated motor. Upon a valid activation, the PLG module supplies power and ground to the motor circuits depending on the liftgate position and the direction the liftgate needs to be moved.
Overhead Console On/Off Switch
The overhead console on/off switch enables or disables the liftgate control switch on the liftgate and activation by the exterior liftgate handle. Both functions are enabled when the PLG module detects ground on the on/off switch circuit from the PLG module. With the overhead console on/off switch in the ON position:
- a ground signal is supplied to the PLG module.
- the liftgate control switch on the liftgate is enabled.
- activation by the exterior liftgate handle is enabled.
The overhead switch has an ignition feed through the SJB fuse 16 (5A). With the ignition in RUN and the on/off switch in the ON position, the LED in the switch will illuminate. With the overhead console on/off switch in the OFF position, the ground is removed and the liftgate control switch on the liftgate and activation by the exterior liftgate handle will not operate.
PLG Control Switch - Overhead Console
Pressing the overhead console PLG control switch supplies a momentary ground signal to the SJB which then unlocks all doors if fully closed. Then a ground signal is sent to the PLG module which will OPEN or CLOSE the liftgate depending on the conditions. The overhead console on/off switch does not affect the PLG control switch in the overhead console.
PLG Close Switch - Liftgate
Pressing the PLG close switch (located on the liftgate trim panel) supplies a momentary ground signal to the PLG module which will CLOSE the liftgate depending on the conditions. The overhead console on/off switch will disable the PLG close switch operation.
Remote Keyless Entry (RKE) Operation
The SJB receives a PLG activation command from the remote keyless entry (RKE) transmitter. The SJB will unlock all the doors (if closed) and then ground the open/close circuit to the PLG module. The signal transmitted between the SJB and the PLG module is not specific to Open or Close operation. The PLG module will determine which operation to carry out depending on the liftgate position when the signal is received.
SJB Interface
PLG open operation requires the vehicle to be in PARK and the vehicle speed to be less than 5 km/h (3 mph). The SJB receives information over the SCP network from the powertrain control module (PCM) for the PRNDL position and from the anti-lock brake system/traction control module (ABS/TC) for the vehicle speed.
If the ignition is in the ON position and if the vehicle is in PARK, the SJB will ground the PARK (enable) circuit to the PLG module. If the vehicle speed is less than 5 km/h (3 mph), the SJB will ground the vehicle speed circuit to the PLG module. As long as these 2 circuits are at ground, normal PLG operation can be carried out.
If the ignition is in the OFF position, the SJB grounds the PARK (enable) and the VSS (enable) circuit to the PLG module which will allow normal operation of the PLG.
The PLG module will not active the PLG if either of these inputs is not grounded. These inputs have network DTCs. If any VSS or transmission range switch DTCs are retrieved and the PLG is not operating, repair these DTCs first.
PLG Operation
The following is a brief explanation of a normal power open cycle of the PLG.
- The power open operation will begin with one of the following methods:
- The SJB receives a momentary ground signal from the PLG overhead console switch
- The SJB receives a signal from the remote transmitter key FOB (double button press)
The PLG module receives signals from the detent switch and forkbolt switches indicating the exterior liftgate handle has been released.
- The PLG module checks the PARK and vehicle speed sensor (VSS) circuits from the SJB for ground.
- The PLG module supplies power to the unlatch actuator which releases the PLG latch. Also, a 5-volt reference is supplied to the position sensor.
- The PLG detent switch, primary forkbolt switch and secondary forkbolt switch circuits are monitored for correct latch release signals.
- Power is supplied to the drive assembly actuator clutch and motor, opening the PLG.
- When the PLG is opening, the position sensor is monitored for liftgate position and velocity. If an obstruction is detected, the liftgate will stop or reverse depending on the conditions.
- The PLG FULL OPEN position is learned by the PLG module during the PLG initialization. When the PLG reaches the FULL OPEN position, the PLG module removes the power from the drive assembly actuator motor and clutch.
The following is a brief explanation of a normal power close cycle of the PLG.
- The power close operation will begin with one of the following methods:
- The SJB receives a momentary ground signal from the PLG overhead console switch
The PLG module receives a momentary ground signal from the rear PLG switch (on the liftgate)
The SJB receives a signal from the remote transmitter key FOB
- The PLG module checks the PARK and vehicle speed circuits from the SJB for ground.
- The PLG module will wait for one second while starting an audible chime before closing the PLG.
- Power is supplied to the drive assembly actuator clutch and motor as the audible chime continues with 3 tones.
- As the PLG is powered closed, the position sensor is monitored for liftgate position and velocity. The PLG will reverse if an obstruction is detected.
- Also, as the PLG is powered closed, the pinch strips are monitored for a pinch condition. The PLG will reverse if an obstruction is detected by either pinch strip.
- The PLG detent switch, forkbolt primary switch and forkbolt secondary switch circuits are monitored for correct latch signals.
- When the PLG module receives switch signals indicating the SECONDARY LATCH position is reached, power is supplied to the cinching actuator and power is removed from the drive motor and clutch to pull the liftgate into the PRIMARY LATCH position.
- When the PLG module receives switch signals indicating the PRIMARY LATCH position is reached, power is removed from the cinching actuator and the liftgate is fully closed.
PLG Chime
The PLG module requests a chime to sound for 3 seconds when:
- the PLG module receives a request to power close.
- the liftgate reverses when closing due to an obstacle.
- the liftgate stops opening due to an obstacle.
The PLG module requests a chime to sound for one second when an open or close input is received when:
- the vehicle speed is greater than or equal to 5 km/h (3 mph).
- the ignition key is in the RUN position and the transmission is not in the PARK position.
- the battery voltage is less than 8 volts.
The chime will sound continuously for up to 5 minutes when the transmission is shifted out of the PARK position or the vehicle speed exceeds 5 km/h (3 mph) while the liftgate is closing. The chime will stop sounding when the liftgate reaches the latch, 5 minutes has elapsed or the transmission is shifted into the PARK position and the vehicle speed is less than 5 km/h (3 mph).
The chime will sound continuously for up to 5 minutes when the liftgate fails to close to the PRIMARY LATCH position after 20 seconds of powering in the close direction. The chime will stop if the liftgate reaches the PRIMARY LATCH position or 5 minutes has elapsed.
PLG Initialization Procedure
If the PLG module loses the logic battery supply for any reason, such as battery disconnect, module disconnect or if left open for more than 6 hours, the PLG module will lose the PLG position stored in memory and will attempt to open when the liftgate switch is pressed the first time.
The PLG normal operation will not be restored until the PLG position is once again stored into memory. The initialization procedure is the learning process the PLG module uses to restore the PLG position in memory. The PLG module monitors the position sensor data received during the initial power open-and-close operation to learn the position.
Refer to Power Liftgate Initialization. Programming and Relearning
PLG Awake/Sleep Status
- The PLG module is in the awake state whenever the ignition is not in the OFF position.
- The PLG module is in the awake state while carrying out a close or an open operation, including cinch.
- The PLG module is in the sleep state when all of the following conditions exist:
- The latch is not in the UNLATCHED position
- The ignition is in the OFF position
- No power operation is active
- No wakeup inputs have changed state for more than 20 seconds
- The PLG module is also in the sleep state when all of the following conditions exist:
- The latch is in the UNLATCHED position
- The ignition is in the OFF position
- No power operation is active
- No wakeup inputs have changed state for more than 6 hours
The wakeup inputs for the PLG are:
- PLG open/close request signal from SJB or liftgate switch
- Forkbolt primary signal
- Forkbolt secondary signal
- Detent switch signal
- Ignition run signal
- Ignition start signal