Trunk lid control, function

P80.20-A006-79

Function requirements, general

 Circuit 30g ON

 No overvoltage or undervoltage

 Trunk lid control normalized

 Speed v < 1km /h (relevant from circuit 15R ON)

 Repeat lock in trunk lid/tailgate lock not active

 Transport mode not activated

 The trunk lid control must be normalized after replacing the trunk lid/liftgate control drive unit or after carrying out adjustment work on the trunk lid.

 The electronic ignition lock control unit sends the status of circuit 15 via interior CAN to the trunk lid control unit. The instrument cluster sends the vehicle speed via user interface CAN, the electronic ignition lock control unit and interior CAN to the trunk lid control unit.

Trunk lid control, general

The trunk lid can be opened and closed automatically from the inside or outside via the trunk lid control. The trunk lid control function includes the following subfunctions:

 Function sequence for opening or closing trunk lid request

 Function sequence for opening trunk lid

 Function sequence for closing trunk lid

 Function sequence for synchronizing trunk lid control

 Function sequence for opening angle limitation

 Function sequence for object recognition

Function sequence for opening or closing trunk lid request

The trunk lid can be opened or closed from the following control points:

 Open trunk lid button on transmitter key (open from outside)

 Driver trunk lid/liftgate control button

 Trunk lid/liftgate control button (close from outside)

 Trunk lid/liftgate external operation switch (open from outside)

 Rear switching module (with code 871 (HANDS-FREE ACCESS))

 Trunk lid emergency opening switch (with code (494) USA version) (trunk lid unlocking only)

 Manual operation ("Tip to run") (as of 02.03.2018)

The trunk lid control unit reads in the each of the operating requirements via interior CAN. If the trunk lid is opened or closed as a result of the request via the rear switching module, the trunk lid control unit actuates the trunk lid/liftgate control warning buzzer 2 times during the trunk lid movement. A warning tone does not sound if the request comes from any other point.

 If the trunk lid control unit reads in another request during opening or closing of the trunk lid, it stops the trunk lid drive. Only when requested again, the drive is continued. Except: Operation with transmitter key. A new request by pressing the open trunk lid button on the transmitter key after stopping always opens the trunk lid.
In vehicles with rear switching module, pressing again after stopping causes the trunk lid to be actuated in the opposite direction.

Open trunk lid button on transmitter key (open from outside)

Vehicles except CODE 889 (KEYLESS-GO):

If the "Open trunk lid" button is pressed on the transmitter key for t > 0.5 s, this transmits a radio signal via the rear window antenna and the antenna amplifier FM 1, AM, CL, and KEYLESS-GO to the electronic ignition lock control unit.

Vehicles with code 889 (KEYLESS-GO):

If the "Open trunk lid" button is pressed on the transmitter key for t > 0.5 s, this transmits a radio signal via the rear window antenna and the antenna amplifier FM 1, AM, CL, and KEYLESS-GO to the electronic KEYLESS-GO control unit. The KEYLESS-GO control unit transmits this signal via the interior CAN to the control unit for the trunk lid control.

The electronic ignition lock control unit checks the transmitter key's access authorization code in both cases. If this is valid, the electronic ignition lock control unit sends the "Open trunk lid" request via the interior CAN to the trunk lid control unit.

 The transmitter key must be located in the direct vicinity of the vehicle. The operation radius of the transmitter key (range of radio signal) corresponds to the central locking function.

Driver trunk lid/liftgate control button

The left front door control unit directly reads in the status of the driver trunk lid/liftgate control button and transmits it to the liftgate control unit and rear SAM control unit via the interior CAN.

Trunk lid/liftgate control button (close from outside)

The rear SAM control unit reads in the status of the trunk lid/liftgate control button directly and sends this via interior CAN to the trunk lid control unit.

 Model 205.0/1/3
with code 881 (Remote boot-lid closing)
with code 889 (KEYLESS-GO)
In addition, the central locking can be locked via the trunk lid/liftgate control button.

Trunk lid/liftgate external operation switch (open from outside)

The rear SAM control unit reads in the status of the trunk lid/liftgate external operation switch directly and sends this via interior CAN to the trunk lid control unit.

Additional function requirements for rear switching module (with CODE 871 (HANDS-FREE ACCESS))

 Circuit 15 OFF

 Transmitter key is located in area of trunk

Rear switching module (with code 871 (HANDS-FREE ACCESS))

The trunk lid can be opened and closed without touching using the rear switching module. The function is triggered by foot motion ("kick motion") in the area of the rear switching module below the bumper. For this purpose a transmitter key must be located in the vicinity.

The rear switching module directly reads in the signals from rear switching module sensors, evaluates them and transmits the corresponding request to the KEYLESS-GO control unit via the KEYLESS-GO LIN. The KEYLESS-GO control transmits this request to the trunk lid control unit via the interior CAN.

The trunk lid control unit actuates the trunk lid/tailgate control buzzer twice when the trunk lid is moved.

Trunk lid emergency opening switch (with code (494) USA version) (trunk lid unlocking only)

This function is always active (regardless of the status of the CL [ZV]) because it is intended to allow the trunk lid to be unlocked by a person trapped in the trunk.

The rear SAM control unit reads in the status of the trunk lid emergency opening switch directly and transmits this via the interior CAN to the trunk lid control unit.

Additional function requirement for manual operation ("Tip to run") (as of 02.03.2018)

 Trunk lid/tailgate lock main catch switch is not engaged in trunk lid lock

Manual operation ("Tip to run") (as of 02.03.2018)

The trunk can be automatically opened or closed via a manual actuation. The function is triggered by pushing or pulling the trunk (lid) in the desired direction.

Actuation is detected by the trunk lid/liftgate control position sensor. The control unit for the trunk lid control directly reads in the signals of the trunk lid/liftgate control position sensor.

 The pushing or pulling direction is relevant for triggering the function, i.e. the operating request must be detected in order to prevent the function from being triggered by a gust of wind, for example.

Additional function requirements for opening trunk lid

 Opening request is present

 Trunk lid unlocked

Function sequence for opening trunk lid

The rear SAM control unit unlocks the trunk lid via the trunk lid/liftgate lock motor.

The trunk lid control unit reads in the respective "Open trunk lid" request via the interior CAN or directly ("Tip to run", as of 02.03.2018). Then the trunk lid control unit actuates the trunk lid/liftgate control electric motor in the open direction until the trunk lid control unit recognizes the upper limit or the opening angle limit. The position of the trunk lid is determined by the rotation angle of the trunk lid/liftgate position sensor.

If the trunk lid control unit does not receive any signals from the trunk lid/liftgate position sensor, the actuation of the trunk lid/liftgate control electric motor is stopped. Manual movement of the trunk lid is possible with slightly increased use of force. The entire trunk lid/liftgate control drive unit must be replaced if defective.

Additional function requirements for closing trunk lid

 Closing request is present

Function sequence for closing trunk lid

The trunk lid control unit reads in the respective "Close trunk lid" request via the interior CAN or directly ("Tip to run", as of 02.03.2018). Then the trunk lid control unit actuates the trunk lid/liftgate control electrical motor in the closing direction until the trunk lid/liftgate lock precatch switch (start power closing) is actuated. The rear SAM control unit reads in the status of the trunk lid/liftgate lock precatch switch directly and transmits the status via the interior CAN to the trunk lid control unit. Then the trunk lid control unit stops the drive.

Then the rear SAM control unit starts the power closing function and actuates the trunk lid lock element until the trunk lid/liftgate lock main catch switch is locked. The trunk lid is now fully closed. The rear SAM control unit directly reads in the status of the trunk lid/liftgate main catch switch.

Function sequence for synchronizing trunk lid control

The trunk lid control must be normalized after replacing the trunk lid/liftgate control drive unit or after carrying out adjustment work on the trunk lid.

Normalization is the basis for association of the current position of the trunk lid in relation to the position determined by the trunk lid control unit. Normalization means learning in the upper and lower end position of the trunk lid (zero position).

Normalizing can be performed automatically and manually. In both cases the procedure must be started via the diagnosis tester.

Automatic normalization

When synchronizing automatically, the trunk lid is opened in one cycle up to the upper end position. When the trunk lid remains still for approx. t = 2 s, this position is learned in as the top end position. Then the trunk lid is closed completely at a constant speed until the trunk lid/liftgate lock safety catch switch is pressed (start power closing). The rear SAM control unit starts the power closing function. The value of the trunk lid/liftgate control position sensor that is read in after actuating the trunk lid/liftgate lock main catch switch is set as the lower end position.

The trunk lid control unit actuates the trunk lid/liftgate control electric motor accordingly.

The rear SAM control unit reads in the status of the trunk lid/liftgate lock safety catch switch and the trunk lid/liftgate main catch switch directly.

Manual normalization

During manual normalization a complete cycle is run through. To normalize the upper end position, it is necessary to start automatic opening of the trunk lid. If the control unit for the trunk lid control detects that the end position (block) has been reached within the normalization range that can be adjusted via the diagnostic tester, the control unit for the trunk lid control actuates the trunk lid/tailgate control electric motor for a further t = 2 s and stores this position as the top end position. Then the trunk lid control unit switches off the trunk lid/liftgate control electric motor, even when the request is still present.

If an obstacle is recognized outside the normalizing limits during the normalization procedure, the trunk lid/liftgate control unit switches off the trunk lid/liftgate control electric motor.

To normalize the upper end position, it is necessary to start automatic closing of the trunk lid. The trunk lid/liftgate control unit actuates the trunk lid/liftgate control electric motor in the closing direction until the trunk lid/liftgate lock safety catch switch (start power closing) is actuated. The rear SAM control unit starts the power closing function.

If the trunk lid is now within the normalizing limits for the lower end position, and the trunk lid/liftgate control position sensor is supplying a plausible value, the value of the trunk lid/liftgate control position sensor that is read in after actuating the trunk lid/liftgate lock main catch switch is set as the lower end position.

The trunk lid control unit actuates the trunk lid/liftgate control electric motor accordingly.

The rear SAM control unit reads in the status of the trunk lid/liftgate lock safety catch switch and the trunk lid/liftgate main catch switch directly.

Function sequence for opening angle limitation

The opening angle limitation function is used to determine a new trunk lid end position (garage position or maximum opening) to prevent damage to the trunk lid by protruding cargo (roof box, surfboard, etc.). The "garage position" is a defined intermediate position (approx. 50 % opening width), which can be switched on and off using a menu in the heat unit or defined as new end position.

The operation takes place via the Audio/COMAND control panel (without code 446 (touchpad only)) or the touchpad (for code 446 (touchpad only)); the display takes place via the Audio/COMAND Display. The head unit reads in the operation signals of the Audio/COMAND control panel (without code 446 (touchpad only)) or the touchpad (for code 446 (touchpad only)) via the telematics CAN and sends the request via the user interface CAN, electronic ignition lock control unit, and interior CAN to the control unit for the trunk lid control.

The head unit generates the corresponding image data and sends a switch-on request to the Audio/COMAND display via telematics CAN. The image data is sent via the LVDS line to the Audio/COMAND display.

Function sequence for object recognition

In order to detect an obstacle during the opening and closing procedure of the trunk lid (e.g. trapping or locking up), the trunk lid control unit evaluates the signals from the trunk lid/liftgate control position sensor and the power consumption of the trunk lid/liftgate control drive unit.

If an obstacle is detected by the control unit for the trunk lid control via the trunk lid/liftgate control position sensor during the closing of the trunk lid, the closing procedure is aborted immediately and actuation takes place in the opposite direction until the start position prior to the current closing procedure is reached. During the opening procedure, actuation is aborted and the trunk lid remains in its current position.