Liftgate control, function - GF80.20-P-0003FL

MODEL 212.2 

Fig 1: Liftgate Control Function Diagram - Model 212.2

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Terminal 30
• No overvoltage or undervoltage
• System synchronized
• Speed v = 0 km/h
• Transport mode not activated (as of 1.6.12)

The speed signal is transmitted by the instrument cluster to the liftgate control unit via the interior CAN.

Detailed information on the operating state of the transport mode is given in the separate function description for energy management.

Normalization of the liftgate control unit is required after replacing a component or performing adjustment operations.

Liftgate control, general 

The liftgate can be opened or closed automatically from inside and outside via the liftgate control.

The liftgate control comprises the following partial functions:

• Function sequence for opening and closing request 
• Function sequence for opening liftgate 
• Function sequence for closing liftgate 
• Function sequence for opening angle limitation 
• Function sequence for obstacle detection 

Function sequence for opening and closing request 

The liftgate can opened and closed from the following control points:

• Open/close liftgate button on transmitter key 
• Driver trunk lid/liftgate control button 
• Liftgate control button (closing from outside) 
• Liftgate external operation switch (opening from outside) 
• Rear switching module (with code (871) Sensors for trunk lid/opening/closing) 

The liftgate control unit reads in the control request via the interior CAN.

If the liftgate is opened or closed by the request from the driver trunk lid/liftgate button, the liftgate open/close button on the transmitter key or the rear switching module (with code (871) sensors for liftgate open/close sensors), the liftgate control unit actuates the liftgate control warning buzzer twice during the motion of the liftgate. If requested via the liftgate external operation switch or liftgate control button, a warning tone does not sound.

If the liftgate control unit reads in another request while the liftgate is opening or closing, the liftgate drive stops. Only when requested again, the drive is continued. Except: Operation with transmitter key When the liftgate close/open button on the transmitter key is actuated again after stopping, the liftgate moves in the opposite direction. If the liftgate is positioned at the limitation point when the liftgate open/close button on the transmitter key is actuated, the liftgate is also moved in the opposite direction.

Open/close liftgate button on transmitter key 

Vehicles without code (889) KEYLESS-GO:

When the liftgate control transmit button on the transmitter key is pressed for t > 0.5 s, t transmits a radio signal (access authorization) via the rear window antenna and FM 1, AM, ZV and KEYLESS-GO antenna. This radio signal (access authorization) is read in by the rear SAM control unit and is relayed to the electronic ignition lock control unit via the interior CAN.

Vehicles with code (889) Keyless Go:

If the trunk lid open/close button on the transmitter key is pressed for t > 0.5 s, it sends a radio signal (access authorization) via the rear window antenna and the FM 1, AM, CL [ZV] and KEYLESS-GO antenna amplifier to the KEYLESS-GO control unit. The KEYLESS-GO control unit sends a radio signal (access authorization) to the electronic ignition lock control unit via interior CAN.

The electronic ignition switch control unit checks the access authorization of the transmitter key. If it is defined as valid, the electronic ignition lock control unit transmits the request "Open liftgate" or "Close liftgate" to the liftgate control unit and rear SAM control unit via the interior CAN.

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.

Tailgate control button 

The rear control units directly reads in the status of the liftgate control button and transmits it to the liftgate control unit via the interior CAN.

On vehicles with code (889) KEYLESS-GO, the central locking can also be locked with the liftgate control button (symbol "Lock"). Detailed information is given in the function description "KEYLESS-GO".

Tailgate external operation switch 

The rear control units directly reads in the status of the liftgate external operation switch and transmits it to the liftgate control unit via the interior CAN.

Rear switching module (with code (871) Sensors for trunk lid/opening/closing) 

The liftgate can be opened and closed without touching using the rear switching module. The function is actuated 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 these signals to the liftgate control unit via the interior CAN.

Function sequence for opening liftgate 

The rear control unit unlocks the rotary tumbler of the liftgate via the liftgate central locking motor. Then the liftgate control unit actuates the electric liftgate control motor in the opening direction until the liftgate control position sensor recognizes the upper limitation point or the opening angle limitation. The position of the liftgate is defined by the rotation angle of the liftgate control position sensor. When the liftgate control unit does not receive signals from the liftgate control position sensor, the actuation is of the liftgate control electric motor is stopped.

Moving the liftgate is possible by hand with slight force If the liftgate control drive unit is defective, it must be replaced completely.

Function sequence for closing liftgate 

The liftgate control unit reads in the request "Close liftgate" via the interior CAN and actuates the liftgate control electric motor in the closing direction until the rear SAM control unit recognizes by means of the liftgate rotary tumbler status that the liftgate rotary tumbler switch has arrested in the liftgate rotary tumbler. Then the rear SAM control unit actuates the liftgate lock element (power closing). The liftgate is now completely closed.

Function sequence for opening angle limitation 

If required, the opening angle of the liftgate can be changed to prevent damaging the liftgate when extending objects are transported (skibox, surfboard, etc.). First open liftgate to desired position to activate the opening angle limitation function. This can be accomplished manually or automatically via the liftgate control.

Manually: After the liftgate is opened manually to the desired position, press liftgate control button for approx. t = 2 s.

Automatically: If the liftgate is opened via the liftgate control, it is necessary to momentarily press the liftgate control button as soon as the liftgate is in the desired position. The liftgate remains in this position. An upright drive is required for activation of the opening angle limitation function. Then press liftgate control button for approx. t = 2 s. In both cases the adjustment of the opening angle of the liftgate is confirmed acoustically via the liftgate control warning buzzer. When the liftgate is opened, it is only opened to this stored position. The opening angle can be limited up to max. s = 20 cm in front of the mechanical stop of the liftgate.

Function sequence for obstacle detection 

To recognize pinching or lock-up during the liftgate locking procedure, the liftgate control unit evaluates the signals from the liftgate control Hall sensors.

If the liftgate control unit recognizes pinching or lock-up while closing, the liftgate control electric motor is reversed and the liftgate is moved back to the initial position. During opening the liftgate control electric motor is switched off and the liftgate remains in the momentary position.