Electrical seat adjustment (ESE) in rear passenger compartment, function

S91.29-4597-79

Function requirements, general

 No overvoltage or undervoltage

 Circuit 15R ON

 If the circuit status "Circuit 15R OFF" is recognized, the CAN decoupler (N164) bridges the voltage supply to the left 1st rear seat row seat adjustment control unit with memory (N25/20) and right 1st rear seat row seat adjustment control unit with memory (N25/21). The seat adjustment of the rear seats is thus still possible with the ignition key removed.

Electrical seat adjustment (ESA), general

The ESA enables the electrical adjustment of the driver and front passenger seat. The following adjustment options are available:

 Head restraint height

 Head restraint inclination

 Backrest inclination

 Leg rest inclination

The respective seat position can also be saved and retrieved again.

The ESA includes the following subfunctions:

 Function sequence for recording seat position

 Function sequence for normalization

 Function sequence for antilock device

 Function sequence for manual adjustment

 Function sequence for storing or retrieving the seat position

 Function sequence for seat position in starting position

Function sequence for recording seat position

The electric motors are equipped with Hall sensors. Their signals are read in directly by the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21) and evaluated. The respective position of the head restraint, backrest and leg rest is recorded by counting the Hall sensor signals during the adjustment procedure.

Additional function requirements for normalization

 Circuit 15R ON

The electronic ignition lock (EZS) control unit (N73) sends the circuit status via interior CAN (CAN B) and CAN decoupler control unit (N164) to the left 1st rear seat row seat adjustment control unit with memory (N25/20) or right 1st rear seat row seat adjustment control unit with memory (N25/21).

Function sequence for normalization

Normalization is the basis for recording of the respective seat and head restraint position by the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21). Normalization must be performed during initial startup or in a denormalized condition.

The following mechanical end points must be moved to in order to carry out normalization:

 Front end points of backrest inclination

Front end points of head restraint inclination

Front end points of leg rest

 Lower end points of head restraint height

To do this, the corresponding button at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or the right 1st rear seat row electrical seat adjustment switch group (S55/12) must be pressed for an additional 250 ms after reaching the mechanical end point. When normalization has taken place, the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row adjustment control unit with memory (N25/21) switches off the corresponding electric motor. During initial startup, normalization is performed using the diagnostic system.

 An adjustment is denormalized if no signal is received from the relevant Hall sensor. The denormalization procedure can also be performed using the diagnostic system.

Function sequence for antilock device

If the signal of the relevant Hall sensor is not received for more than 2 s during an adjustment procedure, this is recognized as blocking and the adjustment procedure is canceled by the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21). Adjustment in the same direction is not possible until the respective button at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or right 1st rear seat row electrical seat adjustment switch group (S55/12) has been released for  2 s. Adjustment in the opposite direction is possible immediately.

Function sequence for manual adjustment

The manual adjustment is performed via the corresponding button at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or the right 1st rear seat row electrical seat adjustment switch group (S55/12).

An adjustment request from the respective button at the left 1st rear seat row electrical seat adjustment switch group (S55/11) or at the right 1st rear seat row electrical seat adjustment switch group (S55/12) is read in directly by the left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21).

The left 1st rear seat row seat adjustment control unit with memory (N25/20) actuates the following seat adjustment motors directly in accordance with the request:

 Left 1st rear seat row head restraint inclination adjustment electric motor (M18/16)

 Left 1st rear seat row head restraint height adjustment electric motor (M18/23)

 Left 1st rear seat row backrest inclination adjustment electric motor (M27/16)

 Left 1st rear seat row leg rest inclination adjustment electric motor (M104)

The right 1st rear seat row seat adjustment control unit with memory (N25/21) actuates the following seat adjustment motors directly in accordance with the request:

 Right 1st rear seat row head restraint inclination adjustment electric motor (M18/17)

 Right 1st rear seat row head restraint height adjustment electric motor (M18/24)

 Right 1st rear seat row backrest inclination adjustment electric motor (M27/17)

 Right 1st rear seat row leg rest inclination adjustment electric motor (M105)

Additional function requirements for storing or retrieving the seat position

 Respective seat has been normalized

Function sequence for storing or retrieving the seat position

The seat position of the left seat in the 1st rear seat row is saved by pressing the left 1st rear seat row memory function button (S55/11s7) and the left 1st rear seat row memory 1 button (S55/11s8) or the left 1st rear seat row memory 2 button (S55/11s9).

The seat position of the right seat in the 1st rear seat row is saved by pressing the right 1st rear seat row memory function button (S55/12s7) and the right 1st rear seat row memory 1 button (S55/12s8) or the right 1st rear seat row memory 2 button (S55/12s9).

The left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21) reads in their status via a direct line and adopts the "Save seat position" request.

To call up a stored seat position of the left seat in the 1st rear seat row, the left 1st rear seat row memory 1 button (S55/11s8) or left 1st rear seat row memory 2 button (S55/11s9) must be pressed until the stored seat position has been reached.

To call up a stored seat position of the right seat in the 1st rear seat row, the right 1st rear seat row memory 1 button (S55/12s8) or right 1st rear seat row memory 2 button (S55/12s9) must be pressed until the stored seat position has been reached.

The left 1st rear seat row seat adjustment control unit with memory (N25/20) or the right 1st rear seat row seat adjustment control unit with memory (N25/21) reads in their status via a direct line and adopts the "Adjust seat position" request.