Electric seat adjustment (ESA [ESV]) in rear, function - GF91.29-P-0010LE

MODEL 221.0 /1 as of model year 09/YoM 08 with CODE (223) Rear bench seat with electrically adjustable outer seats with PRE-SAFE positioning function for outer seats and outer head restraints 

Function requirements, general 

• No engine start (circuit 50 OFF)
• No undervoltage (U < 9.3 V)

The EIS [EZS] control unit (N73) transmits the circuit status via interior CAN (CAN B).

Function description of electric seat adjustment in rear, general 

The electric seat adjustment in rear is described on the left rear seat for left-hand drive vehicles by way of an example, but this also applies for the right rear seat.

On vehicles with electric seat adjustment in the rear the two outer seats of the rear bench seat can be adjusted electrically as follows:

• Seat fore/aft position combined with the backrest inclination
• Seat cushion inclination
• Head restraint inclination
• Lower and raise head restraints

Furthermore, in vehicles with code (276) Memory in rear, it is possible to save and retrieve the particular seat position.

Fault handling 

The rear seats control unit (N25/6) checks the requests for seat adjustments it has received for plausibility. Implausible adjustment requests are rejected. Correct requests for other adjustment functions remain unaffected.

The plausibility of a manual adjustment request for a memory adjustment is checked in the left rear door control unit (N69/3).

The ESA [ESV] in the rear enables the following subfunctions:

• Manual adjustment 
• Saving and retrieving seat positions (with code (276)) 
• Normalizing 
• Position measurement 
• Anti-lock device 
• Adjusting possibility of the front passenger seat from the rear via the right rear seat operation switch group (S55/2) 

Manual adjustment 

The manual adjustment is operated via the left rear seat operation switch group (S55/1). The left rear seat operation switch group is read in by the rear door LIN (LIN B2) on the left by the left rear door control unit. The left rear door control unit transmits the requests from the left rear seat operation switch group to the rear seats control unit via interior CAN. To adjust, hold down switches of left rear seat operation switch group until the desired position is reached. The rear seats control unit actuates, depending on the request, the following ESA [ESV] motors in the rear:

• Left rear head restraint inclination adjustment motor (M18/15)
• Right rear head restraint inclination adjustment motor (M18/16)
• Left rear seat fore/aft adjustment motor (M18/17)
• Right rear seat fore/aft adjustment motor (M18/18)
• Left rear seat cushion inclination adjustment motor (M18/19)
• Right rear seat cushion inclination adjustment motor (M18/20)

Priorities 

The seat adjustment is split into 4 groups and 2 priorities, while 2 groups each actuate one rear seat. Each adjustment in a group is independent from an adjustment in another group. Only one motor per group can be actuated at once. If adjustment requests are received for several adjustments in a group by the rear seats control unit, then the adjustment request with the higher priority is performed.

The priorities are determined as follows:

Group 1

• Left fore/aft adjustment (high priority)

Group 2

• Right fore/aft adjustment (high priority)

Group 3

• Left head restraint adjustment (high priority)
• left angle adjustment (low priority)

Group 4

• Right head restraint adjustment (high priority)
• right angle adjustment (low priority)

Saving and retrieving seat positions (with code (276)) 

Additional function requirements 

• ESA [ESV] in the rear normalized

Store driver seat position function sequence 

There are two button operation options for storing the seat position:

• The memory switch (S55/1s6) is held pressed and then memory 1 switch (S55/1s7), memory 2 switch (S55/1s8), or memory 3 switch (S55/1s9) is pressed for the particular memory.
• Press the memory switch for t > 40 ms. Within 0.2 s ≤t ≤3 s, memory 1 switch, memory 2 switch, or memory 3 switch must then be pressed for the particular memory.

The status of the switches is read in by the left rear door control unit via the left rear door LIN and transmitted to the rear seats control unit via interior CAN. The rear seats control unit stores the current seat position.

Move to stored position, function sequence 

To be able to move to a stored position, memory 1 switch, memory 2 switch, or memory 3 switch must be held pressed until the stored end position has been reached. If the switch is released, the adjustment procedure is terminated immediately. The rear seats control unit actuates the corresponding motors.

Abort conditions 

Moving to a stored position is interrupted when:

• Manual seat adjustment
• When other memory switches are pressed

Synchronizing 

Additional function requirements 

• Circuit 15R ON

Function sequence 

Normalization is important for the assignment of the absolute adjustment position and the position recorded by the rear seats control unit. Normalization must be performed during initial startup or in a denormalized condition.

To carry out the normalization procedure, it is necessary to move to the following mechanical end stops:

• Fore/aft adjustment with combined backrest adjustment to the rear or upper stop
  • Head restraint adjustment to the front stop
  • Angle adjustment to the up-stop

For normalization, the corresponding switch in the left rear seat operation switch group must remain actuated for t = 250 ms after the mechanical end stop has been reached.

Upon successful normalization, the rear seats control unit switches off the corresponding seat adjustment motor.

The normalization procedure should be performed via diagnosis for initial startup. In this case, circuit 15R must be switched on.

Denormalization 

An adjustment is denormalized:

• when the mechanical stop has been passed or
• when the waiting time of at least 5 s after a seat adjustment until battery voltage has been disconnected is not observed or
• when a defective Hall sensor is recognized.

The denormalization procedure can also be performed via diagnosis.

Position measurement 

The seat adjustment motors are equipped with Hall sensors. The signals from the Hall sensors are read in and evaluated by the rear seats control unit.

Anti-lock device 

If a defective Hall sensor is detected for t > 2 s, the corresponding adjustment function is switched off by the rear seats control unit after t = 2 s.

Reactivation in the same adjusting direction is not permitted until the corresponding switch has been released for approx. t ≥2 s. Re-enabling in the opposite direction is possible immediately.

Adjusting possibility of the front passenger seat from the rear via the right rear seat operation switch group (S55/2) 

By actuating the seat adjustment selection switch in the right rear seat operation switch group, the adjustment request is read in over the rear door LIN on the right by the right rear door control unit (N69/4) and sent over the interior CAN to the right front seat control unit. After actuating the seat adjustment selection switch, the front passenger seat adjustment is activated for 10 s and this is indicated by an LED in the seat adjustment selection switch.

The following adjustment functions are possible:

• Seat fore/aft position
• Backrest angle
• Seat height
• Head restraint height

Adjustment requests from the right front door control unit have priority over requests from the left front door control unit or right rear door control unit.

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