Principles of Operation

Power Liftgate

Principles Of Operation

Power and Ground Requirements

NOTE: The Smart Junction Box (SJB) may also be identified as the Generic Electronic Module (GEM).

The SJB fuse 14 (10A) supplies battery logic power required for the software, clutch and internal switching operations. Power is supplied to the motor by Battery Junction Box (BJB) fuse 29 (30A).

Ground for the Liftgate/Trunk Module (LTM) is a separate single connection. Some of the continuous inputs which are at a ground state when on are also used for logic switching.

Power Liftgate Detent Switch, Forkbolt Primary Switch and Forkbolt Secondary Switch

The power liftgate detent switch, forkbolt primary switch and forkbolt secondary switch provide inputs to the LTM in order to determine liftgate latch position. The LTM receives inputs from the power liftgate detent switch, forkbolt primary switch and forkbolt secondary switch in the following manner:

NOTE: The liftgate is in the primary position when the liftgate is in the full closed position. The liftgate is in the unlatch position when the liftgate is open and completely out of the striker. The liftgate can be placed in the unlatched position by lifting up on the liftgate handle.

Latch Switch States:

a The detent switch may be in open or grounded state depending on forkbolt position. The detent switch state changes as the forkbolt rotates.


Manual Latch Release for Power Liftgate

To manually open the power liftgate, due to power latch failure, remove the latch access cover located on the lower center of the liftgate trim panel. Reach in on the right side of opening, and push down on the manual latch release lever.

Unlatch/Cinching Motor

The latch uses a bi-directional motor to accomplish both release and cinch operations. The motor is driven in one direction to cinch and in the opposite direction to release.

During a cinch operation, power is supplied to the unlatch/cinching motor by the Liftgate/Trunk Module (LTM) when the secondary latch position is reached during a power close operation. When the motor activates, it pulls the liftgate into the primary latch position. The LTM removes power from the unlatch/cinching motor when the primary latch position is reached.

During an unlatch operation, power is supplied to the unlatch/cinching motor by the LTM when a valid open command is received.

Sector Gear Switches

The sector gear open switch and sector gear close switch provide input to the LTM in order to determine the position of the sector gear. The sector gear is part of the latch assembly. It is driven by the latch motor and in turn drives the latch mechanism. During a release operation, the LTM deactivates the unlatch/cinching motor once the end of travel is reached. After a release operation, the LTM keeps the latch released until the gate moves away from the vehicle. The LTM then reverses the direction of the unlatch/cinching motor until the sector gear switches indicate the sector gear has returned to the neutral position. Refer to the following table for sector gear switch states:

Sector Gear Switch States:

The drive assembly consists of the following:

Position Sensor

When awake, the LTM 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 LTM constantly supplies the ground. The position sensor has 2 data lines that the LTM monitors to determine the liftgate movement and position. The LTM 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.

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 LTM 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 actuator, allowing the motor to turn the actuator and open or close the liftgate.

Actuator Motor

The drive assembly actuator motor is a reversible motor. Upon a valid activation, the LTM supplies power and ground to the motor circuits depending on the liftgate position and the direction the liftgate needs to be moved.

Power Liftgate Control Switch - Instrument Panel

Pressing the instrument panel power liftgate control switch supplies a momentary ground signal to the LTM which will open or close the liftgate depending on the conditions.

Power Liftgate Rear Control Switch - Quarter Trim Panel

Pressing the power liftgate rear control switch (located on the LH quarter trim panel) supplies a momentary ground signal to the LTM which will close the liftgate depending on the conditions.

Exterior Handle Switch

When the exterior handle switch is activated, the Smart Junction Box (SJB) sends a signal to the LTM which will open the liftgate depending on the conditions.

Remote Keyless Entry (RKE) Operation

The SJB receives a power liftgate activation command (double press) from the Remote Keyless Entry (RKE) transmitter. The SJB will send a signal on the Controller Area Network (CAN) to the power liftgate. The signal transmitted between the SJB and the LTM is not specific to the open or close operation. The LTM will determine which operation to carry out depending on the liftgate position when the signal is received.

Power Liftgate Interface

Power liftgate open operation requires the vehicle to be in PARK and the vehicle speed to be less than 5 km/h (3 mph). The power liftgate receives information over the CAN from the PCM for the PRNDL position and from the Instrument Cluster (IC) (gateway) for vehicle speed. These inputs have network DTCs. If any vehicle speed or transmission range Transmission Range (TR) switch DTCs are retrieved and the power liftgate is not operating, repair these DTCs first.

Power Liftgate Operation

The following is a brief explanation of a normal power open cycle of the power liftgate.

- The power open operation will begin with one of the following methods:
- The LTM receives a momentary ground signal from the power liftgate control switch.
- The SJB receives a signal from the remote transmitter key fob (double button press).
- The LTM receives a signal from the SJB indicating the exterior liftgate handle has been activated.

- The LTM checks the PRNDL position and vehicle speed status from the CAN communication link.
- The LTM supplies power to the unlatch/cinching motor until the sector gear switches indicate end of travel which releases the power liftgate latch.
- The power liftgate 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 power liftgate.
- The power liftgate supplies power to the unlatch/cinching motor while monitoring the sector gear switches to return the sector gear to the neutral position.
- When the power liftgate is opening, the position sensor is monitored for liftgate position and velocity. If an obstruction is detected, the liftgate will stop.
- The power liftgate full open position is learned by the LTM during the power liftgate initialization. When the power liftgate reaches the full open position, the LTM removes the power from the drive assembly actuator motor and clutch.
- After the power is removed from the clutch and drive motor, the position sensor briefly continues to monitor the position of the liftgate. If excessive movement in the closed direction is detected, power is reapplied to the clutch and a continuous chime is initiated and remains on as the liftgate is automatically power closed.
- If the excessive closing movement is detected on 11 successive power open requests, DTC B201A is set and power liftgate operation is disabled until the DTC is cleared.

The following is a brief explanation of a normal power close cycle of the power liftgate.

- The power close operation will begin with one of the following methods:
- The LTM receives a momentary ground signal from the power liftgate control switch.
- The LTM receives a momentary ground signal from the power liftgate rear control switch (LH rear quarter panel).
- The SJB receives a signal from the remote transmitter key fob (double press).

- The LTM checks the PRNDL position and vehicle speed status from the CAN communication link.
- The LTM will start an audible chime.
- After one second of audible chime, power is supplied to the drive assembly actuator clutch and motor as the audible chime continues 3 seconds total.
- As the power liftgate is powered closed, the position sensor is monitored for liftgate position and velocity. The power liftgate will reverse if an obstruction is detected.
- Also, as the power liftgate is powered closed, the pinch strips are monitored for a pinch condition. The power liftgate will reverse if an obstruction is detected by either pinch strip.
- The power liftgate detent switch, forkbolt primary switch and forkbolt secondary switch circuits are monitored for correct latch signals.
- When the LTM receives switch signals indicating the secondary latch position is reached, power is supplied to the unlatch/cinching motor to pull the liftgate into the primary latch position. When primary latch position is reached, power is removed from the drive motor and clutch.
- When the LTM receives switch signals indicating the primary latch position has been reached (liftgate is fully closed), the LTM reverses the direction of the unlatch/cinching motor until the sector gear switches indicate the neutral position.

Power Liftgate Chime

The LTM requests a chime to sound for 3 seconds when:

- the LTM receives a request to power close.
- the liftgate reverses when closing due to an obstacle.
- the liftgate stops opening due to an obstacle.

The LTM 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 between 8 and 9.5 volts.

The LTM requests a continuous chime during a power close immediately after a power open under the following conditions:

- there is excessive weight on the liftgate (snow, ice, bicycle rack, etc...).
- worn/damaged liftgate assist cylinders.
- the LTM incorrectly learned the full open position during the power liftgate initialization procedure.

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 open/ajar. 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.

Power Liftgate Initialization Procedure

If the LTM loses the logic battery supply for any reason, such as battery disconnect, module disconnect or if left open for more than 6 hours, the LTM will lose the power liftgate position stored in memory and will attempt to open when the liftgate switch is pressed the first time.

The power liftgate can also lose position if the following components are removed, adjusted or disconnected:

- Power liftgate motor
- Liftgate hinges
- Power liftgate rod
- Liftgate striker

The power liftgate normal operation will not be restored until the power liftgate position is once again stored into memory. The initialization procedure is the learning process the LTM uses to restore the power liftgate position in memory. The LTM 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.

Power Liftgate Awake/Sleep Status

- The LTM is in the awake state whenever the ignition is in the RUN position.
- The LTM is in the awake state while carrying out a close or an open operation, including cinch.
- The LTM is in the sleep state when all of the following conditions exist:
- The latch is not in the fully 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 LTM 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 power liftgate are:

- Power liftgate open/close switch request signal
- Forkbolt primary signal
- Forkbolt secondary signal
- Detent switch signal
- Rear control switch
- Exterior handle switch
- Glass ajar switch
- CAN