Principles Of Operation
Power Liftgate
Principles Of Operation
Power and Ground Requirements
The Body Control Module (BCM) fuse 9 (10A) supplies battery logic power required for the software and internal switching operations. Power is supplied to the motor by Battery Junction Box (BJB) fuse 7 (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 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.
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 and down on the right side of the latch 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 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 and close switches provide input to the LTM 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 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 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 opens or closes 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 rear quarter trim panel) supplies a momentary ground signal to the LTM which closes the liftgate depending on the conditions.
Exterior Liftgate Switch
Without Intelligent Access (IA)
When the exterior liftgate switch is pressed, the Body Control Module (BCM) sends a signal to the LTM over a hardwired circuit which opens the liftgate only when the doors are unlocked.
With Intelligent Access (IA)
When the exterior liftgate switch is pressed, the Remote Function Actuator (RFA) module activates the power liftgate Intelligent Access (IA) feature. If the conditions allow, the RFA module sends a signal over the Medium Speed Controller Area Network (MS-CAN) to the LTM which opens the liftgate.
Remote Keyless Entry (RKE) Operation
Without Intelligent Access (IA)
The BCM receives a power liftgate activation command (double press) from the Remote Keyless Entry (RKE) transmitter. The BCM sends a signal to the LTM over a hardwired circuit. The signal transmitted between the BCM and the LTM is not specific to the open or close operation. The LTM determines which operation to carry out depending on the liftgate position when the signal is received.
With Intelligent Access (IA)
The RFA module receives a power liftgate activation command (double press) from the Remote Keyless Entry (RKE) transmitter. The RFA module sends a signal over the MS-CAN to the LTM. The signal transmitted between the RFA module and the LTM is not specific to the open or close operation. The LTM determines 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 MS-CAN for the gear selector lever position, ignition position and for vehicle speed. These inputs have network DTCs. If any vehicle speed, ignition switch, or Transmission Range (TR) sensor 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 begins with one of the following methods:
- The LTM receives a momentary ground signal from the power liftgate control switch.
- The BCM receives a signal from the RKE transmitter (double button press).
- The LTM receives a signal from the BCM (without IA) indicating the exterior liftgate handle has been activated.
- The LTM receives a signal from the Remote Function Actuator (RFA) module indicating an Intelligent Access (IA) request.
- The MS-CAN checks the gear selector lever position and vehicle speed status from the MS-CAN.
- The LTM supplies power to the unlatch/cinching motor until the sector gear switches indicate end of travel, releasing the power liftgate latch.
- The power liftgate detent switch, primary forkbolt switch and secondary forkbolt switch circuits are monitored for correct latch release states.
- Power is supplied to the drive 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 stops.
- 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.
- After the power is removed from the 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 motor and a continuous chime is initiated and remains on as the liftgate automatically closes. Replace the liftgate cylinders if they cannot support the liftgate in the fully open position after the power is removed from the drive motor.
- If the excessive closing movement is detected on 11 successive power open requests, DTC B201A sets 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 begins 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 BCM receives a signal from the RKE transmitter (double press).
- The LTM checks the gear selector lever position and vehicle speed status from the MS-CAN.
- The LTM starts an audible chime.
- After one second of audible chime, power is supplied to the drive 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 reverses 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 reverses 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 states.
- When the LTM receives switch states 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.
- When the LTM receives switch states 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 park.
- 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, such as snow, ice or a bicycle rack, on the liftgate.
- worn/damaged liftgate assist cylinders.
- the LTM incorrectly learned the full open position during the power liftgate initialization procedure.
The chime sounds continuously for up to 5 minutes when the transmission is shifted out of park or the vehicle speed exceeds 5 km/h (3 mph) while the liftgate is open/ajar. The chime stops sounding when the liftgate reaches the latch, 5 minutes has elapsed or the transmission is shifted into park and the vehicle speed is less than 5 km/h (3 mph).
The chime sounds 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 stops 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 loses the power liftgate position stored in memory and attempts to open when the liftgate switch is pressed the first time.
The power liftgate can also lose position if the power liftgate motor, liftgate hinges or liftgate striker are removed, adjusted or disconnected.
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 or 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
- Liftgate ajar switch
- MS-CAN