Electrical Seat Adjustment (ESA) - GF91.29-P-0009FRB

Model 257, 290 up to Model year 2021 with code 275 (Memory Package (driver's seat, steering column and mirror)) except code 278 (Fully electric front seats) 

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• No overvoltage or undervoltage

Electrical seat adjustment (ESA), general 

The ESA enables the electrical adjustment of the driver and front passenger seat.

The driver and front passenger seat can be adjusted as follows:

• Seat fore/aft position
• Backrest inclination
• Seat height
• Seat inclination
• Seat cushion length
• Head restraint height

Furthermore, the respective seat position can be stored and called up together with other settings.

Priorities:

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 adjustment requests for several adjustments are received in a group by the driver seat control unit or the front passenger seat control unit, the adjustment request with the highest 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

PRE-SAFE®:

In critical situations, the position of the front passenger seat is adjusted automatically to achieve a favorable occupant position.

The ESA includes the following subfunctions:

• Position detection 
• Normalizing 
• Antilock device 
• Manual setting 
• Saving and retrieving seat positions 
• Head restraint presetting 
• Collision avoidance with bench seat in rear passenger compartment (with code 287 (Folding seat backrests in rear passenger compartment)) 
• Error handling 

Position detection 

The seat adjustment motors are equipped with Hall sensors. The signals from the Hall sensors are read in and evaluated by the driver's seat control unit or the front passenger seat control unit directly. Normalization resets a location counter in the driver's seat control unit or the front passenger seat control unit. During seat adjustments, the driver seat control unit or the front passenger seat control unit defines the adjustment range of the seats by counting the Hall sensor signals.

Additional function requirements for normalization 

• Circuit 15R ON

The electronic ignition lock control unit sends the status of circuit 15 over the interior CAN to the driver seat control unit and to the front passenger seat control unit.

Normalizing 

Normalization is the basis for assigning the instantaneous position to the seat position that is recorded by the driver seat control unit or the front passenger seat control unit. Normalization must be performed during initial startup or in a denormalized condition.

The following mechanical stops have to be moved to for the normalization procedure:

• 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

To this end, the corresponding switch in the switch group, seat adjustment must remain actuated for 250 ms after the mechanical end stop has been reached. Upon successful normalization, the driver seat control unit or the front passenger seat control unit switches off the corresponding seat adjustment motor. During the initial startup, the normalization is performed with the diagnostic tester.

An adjustment is denormalized if the signal of the corresponding Hall sensor is not received. The denormalization procedure can also be performed via diagnosis.

Antilock device 

The driver seat control unit or the front passenger seat control unit continuously monitors the power consumption of the seat adjustment motors. If the power consumption is too high (e.g. due to blocked seat adjustment), the driver seat control unit or the front passenger seat control unit switches off the corresponding seat adjustment motor.

Manual setting 

The manual setting partial function includes the following subfunctions:

• Manual front seat adjustment 
• Front passenger seat manual adjustment from driver's seat 

Manual front seat adjustment 

The front seats are manually adjusted using the respective switch group, seat adjustment. The respective front door control unit reads in the status of the switch group, seat adjustment over the front door LIN and sends the adjustment requests over the interior CAN to the driver's seat control unit or to the front passenger seat control unit. To adjust, hold down the switches in the switch group, seat adjustment until the desired position is reached.

The driver seat control unit or the front passenger seat control unit actuates the following seat adjustment motors directly depending on the request:

• Seat adjustment motor, seat fore/aft adjustment
• Seat adjustment motor, head restraint adjustment'
• Seat adjustment motor, backrest inclination
• Seat adjustment motor for seat cushion length adjustment
• Seat adjustment motor for seat inclination adjustment
• Seat adjustment motor for seat height adjustment

Front passenger seat manual adjustment from driver's seat 

Operating the left or right seat adjustment switch in the left front seat climate control switch group enables you to activate the front passenger seat adjustment function. The front passenger seat can be manually adjusted 10 seconds. If an adjustment is made during this period, the front passenger seat adjustment remains active after the adjustment for another 10 seconds. The driver seat can be adjusted again after 10 s have elapsed without any adjustment being performed, or by operating the left or right seat adjustment switch again.

The left front door control unit reads in the status of the left or right seat adjustment switch over the left front door LIN, and sends the "Front passenger seat adjustment active" signal over the interior CAN to the driver's seat control unit and to the front passenger seat control unit.

To adjust, hold down the switches in the left front switch group, seat adjustment until the desired position is reached. The left front door control unit reads in the status of the left front switch group, seat adjustment over the left front door LIN, and sends the adjustment requests over the interior CAN to the front passenger seat control unit. The front passenger seat control unit directly actuates the corresponding seat adjustment motors to match the request.

All adjustments can be made to the front passenger seat from the driver's seat.

Additional function requirements for saving and retrieving seat positions 

• ESA normalized

Saving and retrieving seat positions 

The seat position can be stored and called up again together with other settings.

There are two options for storing the seat position:

• Press and hold down the front memory function switch and then press memory switch 1, 2 or 3 for the respective memory.
• Press the front memory function switch for 100 ms and release, and then press memory switch 1, 2 or 3 for the respective memory within 0.2 to 3 s.

The respective front door control unit reads in the status of the switches in the front switch group, seat adjustment via front door LIN and sends the request "Store memory position" via interior CAN to the driver seat control unit or the front passenger seat control unit. The driver's seat control unit or front passenger seat control unit uses the signals of the Hall sensors to store the current seat position.

Successful storage of the seat position is confirmed by the instrument cluster speaker with an acknowledgment tone. The request for this is sent by the driver seat control unit or the front passenger seat control unit via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster. The instrument cluster directly actuates the instrument cluster speaker in order to output the acknowledgment tone.

To retrieve saved positions, press and hold corresponding memory switch 1, 2 or 3 until the stored end position is reached. Releasing leads to immediate termination of the adjustment procedure.

The respective front door control unit reads in the status of the switches in the front switch group, seat adjustment via front door LIN and sends the request "Adopt memory position" via interior CAN to the driver seat control unit or the front passenger seat control unit. The driver seat control unit or the front passenger seat control unit actuates the corresponding seat adjustment motors directly.

The adjustment of the memory position is interrupted under the following conditions:

• Manual seat adjustment
• Manual mirror adjustment (driver only)
• Manual steering column adjustment (driver only)
• Pressing other memory switches

Compensating movements: 

If collisions occur despite the defined priorities, compensating movements are started. When adjusting the backrest toward the rear, the seat fore/aft adjustment, seat height adjustment and seat inclination adjustment are ended first and the backrest is then positioned.

When adjusting the seat fore/aft adjustment to the rear, the seat backrest adjustment to the rear and the seat height adjustment upwards, the memory setting is implemented according to the following procedure:

• Seat fore/aft adjustment to the rear up to the characteristic map limit, then seat inclination adjustment
• Stop seat fore/aft adjustment at characteristic map limit
• Seat height adjustment until memory position is reached, then seat inclination adjustment
• Seat fore/aft adjustment until memory position is reached, then seat inclination adjustment
• Seat backrest adjustment until memory position is reached, then seat inclination adjustment

Additional function requirements for head restraint presetting 

• ESA normalized

Head restraint presetting 

The height of the head restraint is automatically preset by the driver seat control unit or by the front passenger seat control unit depending on the seat fore/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.

The head restraint presetting function can be switched on and off using a diagnostic tester and is coded after installation according to the country.

Additional function requirements for collision avoidance with bench in rear passenger compartment (with code 287 (Folding seat backrests in rear passenger compartment)) 

• ESA normalized
• Vehicle speed below 5 km/h
• Circuit 15 Off (driver seat only)

The instrument cluster sends the vehicle speed via user interface CAN, electronic ignition lock control unit and interior CAN to the driver seat control unit and to the front passenger seat control unit.

The electronic ignition lock control unit sends the status of circuit 15 over the interior CAN to the driver seat control unit and to the front passenger seat control unit.

Collision avoidance with bench seat in rear passenger compartment (with code 287 (Folding seat backrests in rear passenger compartment)) 

The status of the backrest at the left/right rear (unlocked or locked) and the backrest inclination is recorded by the rear SAM control unit. To do so, the rear SAM control unit reads in the status of the rear backrest lock switch and the rear backrest inclination switch directly and then sends the status of the respective backrest via interior CAN to the driver seat control unit or to the front passenger seat control unit.

The driver seat control unit or the front passenger seat control unit evaluates the current position of the front seats and checks whether a collision hazard exists with the corresponding front seat when folding down the respective backrest in the rear. If there is a collision hazard with the driver or front passenger seat when folding down the respective backrest, the driver seat control unit or front passenger seat control unit initiates the following measures:

• The driver or front passenger seat is moved forward if it is positioned too far to the rear (seat fore/aft adjustment)
• The driver and front passenger seat backrest are set upright if they are inclined too far (seat fore/aft adjustment)
• The driver or front passenger seat is moved up if it is positioned too far down (seat height adjustment)

The collision avoidance function is interrupted under the following conditions:

• Locking of backrest in rear
• Actuating left front switch group, seat adjustment

If the backrest in the rear is locked again, the corresponding front seat remains in its current position. They are not automatically moved to the initial position.

To trigger the collision avoidance with the rear bench seat function again, the system must detect that the rear backrest has been locked again.

With an unlocked backrest in the rear that is not folded forward, a message is issued by the instrument cluster. The rear SAM control unit sends the status of the respective backrest via interior CAN, electronic ignition lock control unit and user interface CAN to the instrument cluster.

Error handling 

The driver seat control unit or the front passenger seat control unit checks the requests for seat settings it has received for plausibility. Adjustment requests for the same adjustment function in an opposite direction (e.g. backrest inclination forward//back simultaneously) are rejected. Correct requests for other adjustment functions remain unaffected. The plausibility of a manual adjustment request for a memory adjustment is checked by the left front door control unit or the right front door control unit.

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