Principles Of Operation

WARNING: This page is about a different car, the 2015 Lincoln MKT. However, it is still accessible from the selected car via links, so may be relevant.

Power and Ground Requirements

The BCM fuse 8 (10A) supplies battery logic power required for the software, clutch and internal switching operations. Power is supplied to the motor by 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 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

Latch Position

Detent Switch

Forkbolt Secondary Switch

Forkbolt Primary Switch

Fully Unlatched

Open ⁽¹⁾

Grounded

In Secondary

Grounded ⁽¹⁾

Open

Grounded

In Primary

Grounded

Open

⁽¹⁾	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

In the event of an electrical failure with the power liftgate system, the liftgate can still be opened. For instructions, refer to Liftgate Latch Manual Release in Handles, Locks, Latches and Entry Systems .

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 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

Sector Gear Position	Sector Gear Open Switch	Sector Gear Close Switch
End of Travel	Grounded	Grounded
Release	Open	Grounded
Cinch	Grounded	Open
Neutral	Open	Open

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.

Front Power Liftgate Switch

Pressing the front power liftgate switch supplies a momentary ground signal to the LTM which opens or closes the liftgate depending on the conditions.

Rear Power Liftgate Switch

Pressing the power rear liftgate switch supplies a momentary ground signal to the LTM which closes the liftgate depending on the conditions.

Liftgate Release Switch

Pressing the liftgate release switch supplies a momentary ground signal to the RFA module. The RFA module sends a message to the LTM to open the liftgate, depending on the conditions.

Remote Keyless Entry (RKE) Operation

The RFA module receives a power liftgate activation command (double press) from the RKE transmitter. The RFA module sends a message on the Controller Area Network (CAN) to the LTM. The message sent to 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 CAN for the PRNDL position and vehicle speed. These inputs have non-network DTCs if the sensors that ultimately provide this data have failed. If any vehicle speed or Transmission Range (TR) sensor DTCs are retrieved and the power liftgate is inoperative, 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 power liftgate receives a momentary ground signal from the front power liftgate switch.
- The RFA module receives a signal from a programmed RKE transmitter (double button press).
- The LTM receives a signal from the RFA module indicating the liftgate release switch has been pressed.
The LTM checks the PRNDL position and vehicle speed status from the CAN.
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 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 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 begins with one of the following methods:
- The LTM receives a momentary ground signal from the front power liftgate switch.
- The LTM receives a momentary ground signal from the rear power liftgate switch.
- The RFA module receives a signal from a programmed RKE transmitter (double button press).
The LTM checks the PRNDL position and vehicle speed status from the CAN.
The LTM starts 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 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 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 is in RUN 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 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 sounds 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 stops 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 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 following components are removed, adjusted or disconnected:

Power liftgate motor
Liftgate hinges
Power liftgate rod
Liftgate striker

The power liftgate normal operation is not 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 .

Power Liftgate Awake/Sleep Status

The LTM is in the awake state whenever the ignition is in RUN.
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 OFF.
- 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 OFF.
- No power operation is active.
- No wakeup inputs have changed state for more than 6 hours.

The wakeup inputs for the power liftgate are:

Front power liftgate switch signal
Rear power liftgate switch signal
RFA module message (liftgate release switch or RKE signal)
Forkbolt primary signal
Forkbolt secondary signal
Detent switch signal
Liftgate ajar switch
Ignition ON message (CAN)