Electrical seat adjustment (ESA) - GF91.29-P-0009FL

MODEL 212 with CODE 275 (Electrically adjustable front seats memory package) 

Fig 1: Electrical Seat Adjustment Block Diagram - Model 212 With Code 275

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Circuit 15R ON or run-on active
• No overvoltage or undervoltage

Run-on:

If circuit 15R is switched off, the electric seats can still be set for t = 180 s. If, during the run-on time, the circuits status or the door status is changed, the run-on time starts again.

The status of circuit 15 is sent by the electronic ignition lock control unit via interior CAN to the driver seat control unit or front passenger seat control unit.

The door status is recorded by the front door rotary tumbler switch. The respective front door control unit reads in the status of the corresponding front door rotary tumbler switch directly and sends this via interior CAN to the driver seat control unit or the front passenger seat control unit.

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 angle
• Seat height
• Seat inclination
• Head restraint height

The respective settings can also be saved and retrieved.

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 higher priority is carried out.

The priorities are determined as follows:

• Group 1:
  • High priority: Backrest adjustment, head restraint adjustment
  • Low priority: Inclination adjustment (seat sitting surface)
• Group 2:
  • High priority: Fore/aft adjustment, height adjustment
• Group 3:
  • High priority: Steering column fore/aft adjustment, steering column up/down adjustment

PRE-SAFE:

In certain danger situations the front passenger seat is adjusted. Detailed information about this can be found in the "PRE-SAFE Function" function description.

The ESA includes the following subfunctions:

• Function sequence for position recognition 
• Function sequence for normalization 
• Function sequence for antilock device 
• Function sequence for manual adjustment 
• Function sequence for saving seat positions 
• Function sequence for retrieving seat positions 
• Function sequence for head restraint presetting 
• Function sequence for collision avoidance (on model 212.0/1 with code (287) Through-loading feature and on model 212.2) 

Function sequence for position recognition 

The seat adjustment motors are equipped with Hall sensors. The signals from the Hall sensors are read in and evaluated by the driver seat control unit or the front passenger seat control unit directly.

Function sequence for normalization 

Normalization is the basis for assigning the current position to the seat position that is recorded by the driver seat control unit and the front passenger seat control unit. Normalization must be performed during initial startup or in a denormalized condition. For this, the front mechanical end stop of the seat fore/aft position and the backrest angle and the bottom mechanical end stop for the seat inclination, seat height and head restraint height must be moved to.

During the initial startup, the normalization is performed with the diagnostic tester. After denormalization, the normalization procedure can be performed using the adjustment function. To do this, press and hold the corresponding switch in the switch group, seat adjustment for an additional t = 250 ms after reaching the mechanical end stop.

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 this 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 motor directly, reads in the signals of the respective Hall sensor directly in the process and evaluates these. Upon successful normalization, the driver seat control unit or the front passenger seat control unit switches off the corresponding seat adjustment motor.

Function sequence for antilock device 

If the Hall sensor signals are not received for t > 2 s with actuation active, this is evaluated as blocking. The driver seat control unit or front passenger seat control unit then stops the relevant actuation. The same actuation is only permissible again after the request is discontinued (e.g. by releasing the corresponding switch) for t ≥2 s. Any other actuation is permitted immediately.

Function sequence for manual adjustment 

The respective front door control unit reads in the status of the switch in the front switch group, seat adjustment via front door LIN and sends this via interior CAN to the driver seat control unit or the front passenger seat control unit.

In order to make the adjustment, the relevant switch must be pressed until the required position is reached.

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

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

Additional function requirements for saving seat positions 

• ESA normalized

Function sequence for saving seat positions 

There are two options for storing the seat position:

• Press and hold left front memory function switch or right front memory function switch, then press the corresponding memory 1, 2 or 3 switch.
• Press left front memory function switch or right front memory function switch for t > 100 ms and then release, then press the corresponding memory 1, 2 or 3 switch within t ≥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 seat control unit or front passenger seat control unit uses the signals of the Hall sensors to store the current seat position.

When the seat position is saved, the instrument cluster outputs an acknowledgment tone. The request for this is transmitted to the instrument cluster by the driver seat control unit or the front passenger seat control unit via the interior CAN.

As well as the seat position, the following settings are saved:

• Pressure in the air cushion of the lumbar support
• Pressure in the air cushion of the multicontour seats (with code (409) Left/right front multicontour seats)
• Position of the steering column (when saving position of driver seat)
• Adjustment of the outside mirror (when saving position of driver seat)

Detailed information about this can be found in the following separate function descriptions:

• Lumbar adjustment function
• Dynamic multicontour seat, function (with code (409) Left/right front multicontour seats)
• Electrically adjustable steering column (ESC), function
• Electric mirror, function

Additional function requirements for retrieving seat positions 

• ESA normalized

Function sequence for retrieving seat positions 

In order to call up the stored positions, the memory 1, 2 or 3 switch must be pressed until the respective 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 seat adjustment motors accordingly.

In addition to the seat position, the following settings are called up:

• Pressure in the air cushions of the lumbar support
• Pressure in the air cushions of the multicontour seats (with code (409) Left/right front multicontour seats)
• Position of the steering column (when calling up position of driver seat)
• Adjustment of the outside mirror (when calling up position of driver seat)

Detailed information about this can be found in the following separate function descriptions:

• Lumbar adjustment function
• Dynamic multicontour seat, function (with code (409) Left/right front multicontour seats)
• Electrically adjustable steering column (ESC), function
• Electric mirror, function

Abort conditions

Moving to a stored position is interrupted during:

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

Additional function requirements for head restraint presetting 

• Seat fore/aft adjustment normalized
• Head restraint adjustment normalized
• Function switched on through the variant coding

Function sequence for head restraint presetting 

The position of the head restraints is preset by the driver seat control unit or front passenger seat control unit depending on the seat fore/aft position according to the parameters programmed by Development (coupler curve). Because the adjustment speeds of the seat fore/aft and head restraint adjustment are not synchronized, the head restraint is adjusted in several steps during the fore/aft adjustment. If the seat is adjusted forward, the head restraint moves down. If the seat is adjusted back, the head restraint moves up. The head restraint presetting function can be switched on and off using a diagnostic tester and is coded after installation according to the country.

The head restraint adjustment via the front head restraint adjustment switch and the adjustment of a stored position are independent of the head restraint presetting function. If, in addition to the seat fore/aft adjustment, another manual adjustment is executed, the head restraint presetting function is not started or it is ended. If the additional adjustment is ended and the seat fore/aft adjustment is active, the head restraint moves in line with the characteristics map again.

Abort conditions:

The head restraint presetting function is interrupted in the event of manual head restraint adjustment.

Additional function requirements for collision avoidance (on model 212.0/1 with code (287) Through-loading feature and on model 212.2) 

• Normalization of the fore/aft adjustment, height adjustment, and backrest adjustment carried out
• Vehicle speed v < 5 km/h
• Circuit 15 Off (driver seat only)

The instrument cluster sends the vehicle speed via interior CAN to the driver seat control unit and to the front passenger seat control unit.

Function sequence for collision avoidance 

The driver seat control unit and the front passenger seat control unit use the current seat position to evaluate whether there is a risk of collision with the front seats when folding over the rear seat backrest.

They then initiate the following measures, if necessary:

• The seat fore/aft adjustment is moved forward to a specific position if the seat is too far to the rear.
• The backrest is moved to an upright position if it is at too great an incline.
• The seat height adjustment is moved up if the seat is positioned too low.

The release and folding forward of the rear seat backrest is recorded via the rear backrest lock switch and the rear backrest inclination switch. The status of the rear backrest lock switch and the status of the rear backrest inclination switch are read in directly by the rear SAM control unit and sent via interior CAN to the driver seat control unit and the front passenger seat control unit.

With code (494) USA version:

If the rear seat backrest is not locked, adjustment in the collision zone is not possible.

If the rear seat backrest is locked again, the driver seat and the front passenger seat remain in their current position. They are not automatically moved to the initial position. The seat fore/aft adjustment is possible when the rear seat backrest is locked over the entire adjustment range.

Abort conditions:

The collision avoidance with the rear seat function is aborted upon:

• Locking the rear backrest
• Actuation of left front switch group, seat adjustment or right front switch group, seat adjustment

After interruption of the collision avoidance function with the rear seat, the front seats on vehicles with code (494) USA version, can be adjusted without limitation. In vehicles without code (494) USA version, a manual adjustment into the collision zone during the collision avoidance function is possible. The seat adjustment is coded following installation depending on the country.

To trigger the collision avoidance with the rear seat function again, the rear backrest must again be recognized as unlocked.