Trunk / Liftgate: Description and Operation

Body Closures

Component Location

LTM (Liftgate/Trunk Module)










Overview

The power liftgate feature allows power opening or closing of the liftgate by using any of the following:
- instrument panel control switch
- the liftgate button on a RKE (Remote Keyless Entry) transmitter
- exterior liftgate switch (open only)
- rear liftgate switch (close only)

System Operation

System Diagram





Network Message Chart

Module Network Input Messages - LTM (Liftgate/Trunk Module)






Power Open

The power liftgate power open operation begins when the LTM (Liftgate/Trunk Module) receives an input from one of the following:
- The LTM (Liftgate/Trunk Module) receives a momentary ground signal from the instrument panel power liftgate switch.
- The BCM (Body Control Module) receives a signal from the RKE (Remote Keyless Entry) transmitter (double button press).
- The LTM (Liftgate/Trunk Module) receives a signal from the BCM (Body Control Module) (without IA (Intelligent Access)) indicating the exterior liftgate handle has been activated.
- The LTM (Liftgate/Trunk Module) receives a MS-CAN (Medium Speed Controller Area Network) message from the RFA (Remote Function Actuator) module indicating an IA (Intelligent Access) request.

Once the LTM (Liftgate/Trunk Module) receives an open request, it opens the power liftgate by carrying out the following:
- The LTM (Liftgate/Trunk Module) checks the gear selector lever position and vehicle speed status from the MS-CAN (Medium Speed Controller Area Network).
- The LTM (Liftgate/Trunk Module) 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 LTM (Liftgate/Trunk Module) 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 (Liftgate/Trunk Module) during the power liftgate initialization. When the power liftgate reaches the full open position or a customer programmed open height, the LTM (Liftgate/Trunk Module) 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.

Power Close

The power liftgate power close operation begins when the LTM (Liftgate/Trunk Module) receives an input from one of the following:
- The LTM (Liftgate/Trunk Module) receives a momentary ground signal from the instrument panel power liftgate switch.
- The LTM (Liftgate/Trunk Module) receives a momentary ground signal from the rear power liftgate switch.
- The BCM (Body Control Module) receives a signal from the RKE (Remote Keyless Entry) transmitter (double button press).

Once the LTM (Liftgate/Trunk Module) receives an close request, it closes the power liftgate by carrying out the following:
- The LTM (Liftgate/Trunk Module) checks the gear selector lever position and vehicle speed status from the MS-CAN (Medium Speed Controller Area Network).
- The LTM (Liftgate/Trunk Module) starts an audible chime.
- After 1 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, primary forkbolt switch and secondary forkbolt switch circuits are monitored for correct latch states.
- The LTM (Liftgate/Trunk Module) 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 (Liftgate/Trunk Module) receives switch states indicating the primary latch position has been reached (liftgate is fully closed), the LTM (Liftgate/Trunk Module) reverses the direction of the unlatch/cinching motor until the sector gear switches indicate the neutral position.

If any of the power liftgate switches or the button on the RKE (Remote Keyless Entry) transmitter is pressed during a power close, the liftgate stops and holds its position.

Programmable Power Liftgate Open Height

The power liftgate system has a feature that allows the power open height to be programmed. Once the open height is programmed, the liftgate power opens only to the programmed height. Once the liftgate has stopped at the programmed open height, it can be manually moved to a different height. The programmed open height remains stored even when the battery is disconnected.

REFER to Program Power Liftgate Open Height Procedures.

Liftgate Latch Manual Release

In the event of a failure with the power liftgate system, the liftgate can still be opened. REFER to Liftgate Latch Manual Release Liftgate Latch Manual Release.

Component Description

Power Liftgate Switch - Instrument Panel

The instrument panel power liftgate switch is a momentary contact switch that supplies a ground signal to the LTM (Liftgate/Trunk Module) when it is pressed. Pressing this switch either opens or closes the power liftgate depending upon the conditions.

Power Liftgate Switch - Rear

The rear power liftgate switch is a momentary contact switch that supplies a ground signal to the LTM (Liftgate/Trunk Module) when it is pressed. Pressing this switch closes the power liftgate depending upon the conditions.

Power Liftgate Switch - Exterior

The exterior power liftgate switch is a momentary contact switch that supplies a ground signal to either the BCM (Body Control Module) (without IA (Intelligent Access)) or the RFA (Remote Function Actuator) module (with IA (Intelligent Access)).

Without IA (Intelligent Access)

When the exterior liftgate switch is pressed, the BCM (Body Control Module) sends a signal to the LTM (Liftgate/Trunk Module) over a hardwired circuit which opens the liftgate only when the doors are unlocked.

With IA (Intelligent Access)

When the exterior liftgate switch is pressed, the RFA (Remote Function Actuator) module activates the power liftgate IA (Intelligent Access) feature. If the conditions allow, the RFA (Remote Function Actuator) module sends a signal over the MS-CAN (Medium Speed Controller Area Network) to the LTM (Liftgate/Trunk Module) which opens the liftgate.

Pinch Strip Switch

The power liftgate pinch strips are membrane style switches. When the switch is pressed the contacts inside the switch make contact and send a ground signal to the LTM (Liftgate/Trunk Module) indicating that there is an obstacle preventing the liftgate from closing. When the pinch strip is not pressed, it has an approximate resistance of 2500-10,500 ohms.

Power Liftgate Chime

The power liftgate chime provides audible warnings to the operator. It is mounted on the LTM (Liftgate/Trunk Module) and is not serviceable separately.

The power liftgate feature sounds an audible chime for 3 seconds whenever:
- the liftgate is requested to begin power closing
- the liftgate reverses to power opening due to an obstacle
- the liftgate stops opening due to an obstacle

The power liftgate feature sounds an audible chime for 1 second whenever there is an open/close request and:
- the vehicle speed is above 5 km (3.11 mi)
- the ignition is in RUN or the transmission is not in park
- the battery voltage is low

Power Liftgate Latch

The power liftgate latch is responsible for latching, unlatching, and cinching the liftgate. The power liftgate latch contains the unlatch/cinching motor, detent switch, forkbolt primary and secondary switches, and the sector gear switches.

Unlatch/Cinching Motor

The latch uses a bi-directional motor to accomplish both unlatch and cinch operations. The motor is driven in one direction to cinch and in the opposite direction to unlatch. During a cinch operation, power is supplied to the unlatch/cinching motor by the LTM (Liftgate/Trunk Module) 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 (Liftgate/Trunk Module) 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 (Liftgate/Trunk Module) when a valid open command is received.

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 (Liftgate/Trunk Module) to determine liftgate latch position. 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 LTM (Liftgate/Trunk Module) receives inputs from the power liftgate detent switch, forkbolt primary switch and forkbolt secondary switch in the following manner:

NOTE: The detent switch may be in an open or grounded state depending on forkbolt position. The detent switch state only changes as the forkbolt rotates.






Sector Gear Switches

The sector gear open and close switches provide input to the LTM (Liftgate/Trunk Module) 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 (Liftgate/Trunk Module) deactivates the unlatch/cinching motor once the end of travel is reached. After a release operation, the LTM (Liftgate/Trunk Module) keeps the latch released until the gate moves away from the vehicle. The LTM (Liftgate/Trunk Module) 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:






Power Liftgate Motor

The power liftgate motor is responsible for raising and lowering the liftgate. The power liftgate motor is a bi-directional motor and contains a position sensor that provides input back to the LTM (Liftgate/Trunk Module) for liftgate position and velocity.

Position Sensor

The LTM (Liftgate/Trunk 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 LTM (Liftgate/Trunk Module) constantly supplies the ground. The position sensor has 2 data lines that the LTM (Liftgate/Trunk Module) monitors to determine liftgate movement and position. The LTM (Liftgate/Trunk 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.

Liftgate Or Trunk Module (LTM)

The LTM (Liftgate/Trunk Module) is responsible for opening or closing the power liftgate based on the inputs it receives. Based on the inputs, it determines if conditions allow a power open or power close.

The BCM (Body Control Module) supplies battery logic power required for the software and internal switching operations. Power is supplied to the motor and latch by BJB (Battery Junction Box). Ground for the LTM (Liftgate/Trunk 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.

The LTM (Liftgate/Trunk Module) does not require PMI (Programmable Module Installation) when it is replaced.