Liftgate Control, Function - GF80.20-P-0003RF

Model 205.2, 253 

with code 890 (EASY-PACK-tailgate) 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• No overvoltage or undervoltage
• Liftgate control normalized
• Speed v < 1 km/h (relevant as of circuit 15R ON)
• Play protection in liftgate latch inactive
• Transport mode not activated

The liftgate control must be normalized after replacing the trunk lid/liftgate control drive unit or the liftgate Control unit, or after adjustment operations on the liftgate.

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

Liftgate control, general 

The liftgate can be opened or closed automatically from inside and outside via the liftgate control. The liftgate control function 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 synchronizing 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 liftgate 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)) 
• Manual operation ("Tip to run") 

The liftgate Control unit reads in each control request via interior CAN. If the liftgate is opened or closed as a result of the request via the rear switching module (with CODE 871 (HANDS-FREE ACCESS)), the transmitter key, or the driver trunk lid/liftgate control button, the liftgate Control unit actuates the trunk lid/liftgate control warning buzzer 2 times during the liftgate movement. A warning tone does not sound if the request comes from any other point.

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. If, during the opening and closing procedure of the liftgate, an additional request is received, the liftgate Control unit stops the liftgate drive. If the transmitter key is in close proximity and a further request is received, the drive continues in the opposite direction. If the transmitter key is not within close proximity and a further request is received, the drive continues in the opening direction, provided that actuation in the closing direction was previously triggered. Otherwise no actuation takes place.

On vehicles with CODE 871 (HANDS-FREE ACCESS), the liftgate Control unit actuates the liftgate in the opposite direction when actuated again after stopping.

Open liftgate button on transmitter key (open from outside) 

Vehicles except CODE 889 (KEYLESS-GO):

If the liftgate open button on the transmitter key is pressed for t > 0.5 seconds, it sends a radio signal via the rear window antenna and the FM 1, AM, CL [ZV] and KEYLESS-GO antenna amplifier to the electronic ignition lock Control unit.

Vehicles with CODE 889 (KEYLESS-GO):

If the liftgate open button on the transmitter key is pressed for t > 0.5 seconds, it sends a radio signal via the rear window antenna, the FM 1, AM, CL [ZV] and KEYLESS-GO antenna amplifier, the KEYLESS- GO Control unit and interior CAN to the electronic ignition lock Control unit.

The electronic ignition lock Control unit checks the transmitter key's access authorization code in both cases. If it is valid, the electronic ignition switch Control unit transmits the request "Open liftgate" to the liftgate Control unit via the interior CAN.

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 sends this via interior CAN to the liftgate Control unit and the rear SAM Control unit.

Trunk lid/liftgate control button (close from outside) 

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

In addition the central locking (CL) can be locked via the trunk lid/liftgate control button.

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

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

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

• Circuit 15 OFF
• Transmitter key is located near the liftgate

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

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 the transmitter key should be in the KEYLESS-GO range.

The rear switching module directly reads in the signals from the rear switching module sensors, evaluates them and sends the corresponding request via the KEYLESS-GO LIN, the KEYLESS-GO Control unit and interior CAN to the liftgate Control unit.

The liftgate Control unit actuates the trunk lid/liftgate control warning buzzer 2 times as the liftgate is moving.

Additional functional requirements for manual operation ("Tip to run") 

• The trunk lid/liftgate lock main catch switch is not engaged in the liftgate latch

Manual operation ("Tip to run") 

The liftgate can be opened and closed automatically via manual actuation. This function is triggered by pressing or pulling the liftgate in the desired direction.

The actuation is detected by the trunk lid/liftgate control Hall sensor. The liftgate Control unit directly reads in the signals from the trunk lid/liftgate control Hall sensor.

The pushing or pulling direction is relevant for triggering the function, i.e. the control 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 liftgate 

• Opening request is present
• Liftgate unlocked

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

Function sequence for opening liftgate 

The liftgate Control unit reads in the respective opening request via the interior CAN or directly ("Tip to run"), evaluates it, and actuates the trunk lid/liftgate control electric motor in the opening direction until the liftgate Control unit recognizes the upper limitation point or the opening angle limitation. The position of the liftgate is determined by evaluating the signals from the trunk lid/liftgate Hall sensor.

When the liftgate Control unit does not receive signals from the trunk lid/liftgate control Hall sensor, actuation of the trunk lid/liftgate control electric motor is stopped. Manual motion of the liftgate is possible with slightly increased force. The entire trunk lid/liftgate control drive unit must be replaced if defective.

Additional function requirements for closing liftgate 

• Closing request is present

Function sequence for closing liftgate 

The liftgate Control unit reads in the closing request via the interior CAN or directly ("Tip to run") and actuates the trunk lid/liftgate Control unit in the closing direction until the trunk lid/liftgate lock is actuated (power closing start). The rear SAM Control unit directly reads in the status of the trunk lid/liftgate lock safety catch switch and sends it via interior CAN to the liftgate Control unit. Then the liftgate Control unit stops the drive.

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

Function sequence for synchronizing liftgate 

The liftgate control must be normalized after replacing the liftgate control drive unit or after adjustment work on the liftgate.

Normalization is the basis for assignment of the current position to the liftgate Control unit position detected by the driver seat Control unit. Normalization means learning in the upper and lower end position of the liftgate (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 liftgate is opened in one cycle up to the upper end position. When the liftgate stands still for approx. t = 2 s, this position is learned in as the upper end position. The liftgate is then fully closed at a constant speed until the trunk lid/liftgate lock safety catch switch is actuated (start of power closing). The rear SAM Control unit starts the power closing function. The rear SAM Control unit then starts the power closing function. The value from the trunk lid/liftgate control Hall sensor read in after actuating the trunk lid/liftgate lock main catch switch is set as the lower end position.

The liftgate Control unit actuates the liftgate control electric motor accordingly.

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 liftgate. When the liftgate recognizes when the end position (locked) is reached within the adjustable normalization range to be adjusted with the diagnosis tester, the liftgate Control unit actuates the liftgate control electric motor for another t = 2 s and stores this position as the upper end position. Then the liftgate Control unit switches off the 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 liftgate Control unit switches off the liftgate control electric motor.

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

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

If an obstacle is recognized outside the normalizing limits during the normalization procedure, the liftgate Control unit switches off the liftgate control electric motor. In this case it is necessary to renormalize.

During the normalization procedure, the opening angle limitation is deactivated.

Function sequence for opening angle limitation 

The opening angle limitation function is intended to determine a new end position of the liftgate (garage position or maximum opening) to prevent damage to the liftgate caused by protruding transport goods (ski box, 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.

Manual 

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

Automatic 

If the liftgate is opened via the liftgate control, it is necessary to quickly press the liftgate control button once as soon as the liftgate is in the desired position. The liftgate remains in this position. A stopped drive is required for activation of the opening angle limitation function. Then press liftgate control button for approx. t = 2 s. The liftgate Control unit reads in actuation of the liftgate control button via the interior CAN, switches off the liftgate control electric motor and stores the current position of the liftgate as upper opening angle limitation. For this purpose the liftgate Control unit evaluates the signals from the liftgate position sensor.

Successful storage of the value for the opening angle limitation is confirmed by outputting a warning tone over the liftgate control warning buzzer. For this purpose the liftgate Control unit directly actuates the liftgate control warning buzzer.

When the liftgate is opened, it is only opened to this stored position. Opening the liftgate can be limited to approx. s = 20 cm before the upper end position.

Function sequence for obstacle detection 

In order to recognize an obstacle (pinching or locking up) during the opening and closing procedure of the liftgate, the liftgate Control unit evaluates the signals from the trunk lid/liftgate control Hall sensor and the power consumption of the trunk lid/liftgate control drive unit.

If an obstacle is recognized by the liftgate Control unit via the trunk lid/liftgate control Hall sensor when the liftgate is closing, the closing procedure is immediately aborted and brief actuation in the opposite direction is triggered. During the opening procedure, actuation is aborted and the liftgate remains in its current position.