Front seat electrical seat adjustment, basic function

Overview:

This document contains information on:

 General

 Function requirements

 Manual seat adjustment

 Seat adjustment prioritization

 Front passenger seat manual adjustment from driver's seat/passenger side rear seat (depending on equipment)

 Normalize (seat with memory function)

 Position detection (seat with memory function)

 Anti-lock protection (seat without memory function)

 Anti-lock protection (seat with memory function)

 Head restraint presetting

 Collision avoidance with bench seat in rear (depending on equipment)

 Actuation by other systems

General

Electrical seat adjustment makes it possible to adjust the seat by actuating motors which move individual parts of the seat into the desired position. Depending on the model and equipment involved, the following settings are possible:

 Seat longitudinal direction

 Seat cushion length

 Seat cushion inclination

 Seat height

 Backrest inclination

 Head restraint height, longitudinal direction, and inclination

The electric seat adjustment is controlled by the respective seat control unit.

Function requirements

 Circuit 30 t

 No overvoltage or undervoltage

Manual seat adjustment

The front seats are manually adjusted using the respective front switch group, seat adjustment in the doors. The seat control unit for each seat directly actuates the corresponding seat adjustment motors as requested.

The seat control unit checks the received requests for seat adjustments in terms of plausibility. Adjustment requests for the same adjustment function in an opposite direction (e.g. simultaneous seat backrest inclination forward//back) are canceled by the seat control unit. Correct requests for other adjustment functions remain unaffected.

Seat with memory function: The respective front door control unit checks the plausibility of a manual adjustment request for a memory adjustment.

Seat adjustment prioritization

The seat adjustment is divided up into three groups and two priorities. Each adjustment in a group is independent from an adjustment in another group. If several adjustment requests are received by the seat control unit in a group, the adjustment request with the higher priority is carried out.

The priorities are determined as follows:

Group 1:

 High priority: seat fore/aft adjustment, steering column fore/aft adjustment (driver seat only)

 Low priority: seat inclination adjustment

Group 2:

 High priority: backrest inclination, steering column adjustment up/down (driver's seat only)

 Low priority: Seat height adjustment

Group 3:

 High priority: head restraint adjustment, seat cushion length

Front passenger seat manual adjustment from driver's seat/passenger side rear seat (depending on equipment)

The function is used, e.g. in the following cases:

 Chauffeur mode

In order to have maximum legroom and overview at the rear seat on the front passenger side, the front passenger seat and backrest are moved and folded forward as far as permissible.

 Use of fully reclined position on reclining rear seat

The function is activated via a switch in the driver's side seat climate control switch group or the front passenger side rear seat climate control switch group. After activation, the function remains active for 30 s. Within the activation period, the respective seat adjustment switch group can be used to adjust the front passenger seat. If an adjustment is made during this period, front passenger seat adjustment remains active for another 30 seconds after the adjustment. The function switches off after 30 s without an adjustment request or by pressing the switch in the seat climate control switch group again.

When calling up the function from the rear seat, only the following settings are available:

 Backrest inclination

 Seat fore/aft adjustment

 Head restraint height

When adjusting the fully reclined position for the reclining rear seat, the front passenger seat is adjusted automatically.

Normalize (seat with memory function)

Additional function requirements:

 Circuit 15R ON

Normalizing is the basis for assigning the current position to the position of the seat as sensed by the seat control unit.

Normalization is required in the following situations:

 Startup

 In a denormalized condition

Normalization is performed by moving to the following mechanical end stops for more than 250 ms:

 Front end stop of seat fore-and-aft position and seat backrest inclination

 Downstop of seat height and head restraint height

 Upper stop of seat inclination

 Rear end stop of seat cushion length

Upon successful normalization, the seat control unit switches off the corresponding seat adjustment motor. During the commissioning process, normalization is performed using the diagnostic tester.

Denormalization takes place if the signal from the corresponding Hall sensor is not received. Denormalization can also be performed using the vehicle diagnosis system.

Position detection (seat with memory function)

The seat adjustment motors are equipped with Hall sensors. The seat control unit reads in the signals from the Hall sensors and evaluates them. Normalization resets a location counter in the seat control unit to zero. When seat adjustments are made, the seat control unit determines the adjustment travel for the seats by evaluating the Hall sensor signals.

Anti-lock protection (seat without memory function)

Because electrical seat adjustment does not have a sensor system, anti-lock protection is actuated by a thermal fuse in the seat adjustment motors. In the event of blocking, the respective seat adjustment motor is only switched off once it exceeds a certain temperature threshold.

Anti-lock protection (seat with memory function)

The seat control unit monitors the seat's change in position during adjustment with the help of Hall sensors. If blocking is detected, the seat control unit switches off the corresponding seat adjustment motor.

During seat longitudinal, seat height and seat backrest inclination adjustment, the seat control unit also monitors the power consumption of the seat adjustment motors. When the power consumption is too high (e. g. through seat adjustment blocking) the seat control unit switches off the corresponding seat adjustment motor.

Head restraint presetting

Additional function requirements:

 Head restraint normalized

The seat control unit adjusts the height of the head restraint automatically depending on the position in the seat fore-and-aft position. If the seat is moved forward, the head restraint moves down. If the seat is moved back, the head restraint moves up. The head restraint is adjusted in stages.

Collision avoidance with bench seat in rear (depending on equipment)

Additional function requirements:

 Seat adjustment normalized

 Vehicle speed below 12 km/h

 Circuit 15 off (only for driver's seat)

The respective seat control unit evaluates the current position of the front seats and checks whether there is a risk of collision in the rear passenger compartment when folding over the seat backrest. If there is a risk that folding over the respective seat backrest will cause it to collide with the driver's or front passenger seat, the seat control unit initiates the following measures:

 The seat control unit moves the driver's or front passenger seat forward if this is positioned too far back (seat fore/aft adjustment).

 The seat control unit rights the seat backrest of the driver's or front passenger seat if this is inclined too far (seat backrest adjustment).

The collision avoidance function is canceled under the following conditions:

 Locking of the seat backrest in the rear passenger compartment.

 Operating the front left seat adjustment switch group.

If the backrest in the rear is locked again, the corresponding front seat remains in its current position. The front seat automatically returns to its starting position.

With the seat backrest folded forward in the rear passenger compartment, the instrument cluster issues a message depending on the backrest position.

Actuation by other systems

Electrical seat adjustment can also be actuated by the following systems:

 Memory function

 Revitalization

 Preventive occupant protection system