Electric seat adjustment (ESA) function

Function requirements, general

 No overvoltage or undervoltage

 No engine start (circuit 50 OFF)

 The EIS [EZS] control unit (N73) transmits the circuit status and the on-board power supply voltage via interior CAN.

Electric seat adjustment function description, general

The seat adjustment is described at the driver seat for left-hand drive vehicles as an example; the same is valid for the front passenger seat.

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The driver seat on vehicles with code (275), and also the front passenger seat on vehicles with code (242), can be adjusted electrically as follows:

- Seat fore/aft position

- Backrest angle

- Seat height

- Seat inclination

- Head restraint height

Moreover, it is possible to store and move to the particular seat position.

 On the driver-side, the positions of the outside mirrors and the steering column are also stored and retrieved via the memory function.

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Priorities

The seat adjustment is divided up into 2 groups and 3 priorities. Each adjustment in a group is independent from an adjustment in another group.

If adjustment requests for various adjustments are received in a group by the driver-side front seat adjustment control unit with memory (N32/1), then the adjustment request with the higher priority is executed.

The priorities are determined as follows:

Group 1

Priority high, backrest adjustment

Priority average, head restraint

Priority low, inclination adjustment

Group 2

Priority high, fore/aft adjustment

Priority average, height adjustment

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Fault handling

The driver-side front seat adjustment control unit with memory checks the requests received for seat adjustments for plausibility. Adjustment requests for the same adjustment function in an opposite direction (e.g. backrest adjustment forward//back simultaneously) are rejected. Correct requests for other adjustment functions remain unaffected.

The electric seat adjustment enables the following subfunctions:

 Manual adjustment

 Saving and retrieving seat positions

 Head restraint presetting (not ECE and UK)

 Synchronizing

 Position measurement

 Anti-lock device

 Rear easy entry

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Manual adjustment

The manual adjustment is operated using the left front door seat adjustment switch group (memory) (S91/2). The switch group is read in directly by the left front door control unit (N69/1). The left front door control unit sends the adjustment requests via the interior CAN to the driver-side front seat adjustment control unit with memory. For adjustment, the switches of the left front door seat adjustment switch group (memory) have to be pressed and held until the desired position is reached.

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Depending on the request, the driver-side front seat adjustment control unit with memory discretely actuates the following ESA [ESV] motors:

- forward/back motor (M27m1)

- rear raise/lower motor (M27m2)

- front up/down motor (M27m3)

- head restraint raise/lower motor (M27m4)

- backrest motor (M27m5)

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Saving and retrieving seat positions

Additional function requirements

- Normalized electric seat adjustment

Store driver seat position function sequence

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

- Press and hold the memory switch (S91/2s9) and then press the memory 1, 2, 3 switch (S91/2s14) for the respective memory location

- Press the memory switch for t > 100 ms. Within 0.2 s  t  3 s, the memory 1, 2, 3 switch must then be pressed for the respective memory

Successful storage of the seat position is acknowledged by the instrument cluster (A1) with an acknowledgment tone.

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The status of the switches is read in voltage-coded by the left front door control unit and sent via the interior CAN to the driver-side front seat adjustment control unit with memory. The driver-side front seat adjustment control unit with memory stores the current seat position.

Move to stored position, function sequence

To move to a stored position, the corresponding memory 1, 2, 3 switch has to be pressed and held until the stored end position is reached. If the switch is released, the adjustment procedure is terminated immediately.

Abort conditions

Moving to a stored position is interrupted when:

- Manual seat adjustment

- Manual mirror adjustment (only driver)

- Manual steering column adjustment (only driver)

- When additional memory switches are pressed

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Head restraint presetting (not ECE and UK)

Additional function requirements

- Normalized seat fore/aft position

- Normalized head restraint height

Function sequence

The height of the head restraint is automatically preset by the driver seat adjustment control unit with memory depending on the seat fore/aft position. If the seat is adjusted forward, the head restraint moves down. If the seat is adjusted rearward, the head restraint moves up. The head restraint is adjusted in stages.

The head restraint presetting function can be switched on and off in the driver-side front seat adjustment control unit with memory using the diagnosis and is coded country-specifically using the SCN (Software Calibration Number) at the end of the assembly line.

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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 driver-side front seat adjustment control unit with memory. 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:
- Front end stop of fore/aft adjustment and backrest adjustment

- Downstop of inclination adjustment, height adjustment, and head restraint adjustment

For normalization, the corresponding switch in the left front seat adjustment switch group (memory) must remain actuated for
t = 250 ms after the mechanical end stop has been reached.

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Upon successful normalization, the driver-side front seat adjustment control unit with memory switches the corresponding seat adjustment motor off.

The normalization can also be performed via diagnosis. In this case, circuit 15R must be switched on.

 An adjustment is denormalized, if the signal of the corresponding Hall sensor is not received. The Hall sensors are allocated to the particular adjustment motors. The denormalization procedure can also be performed via diagnosis.

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Position measurement

The seat adjustment motors are equipped with Hall sensors. The signals from the Hall sensors are read in and evaluated by the driver-side front seat adjustment control unit with memory.

Anti-lock device

If a defective Hall sensor is detected for t > 2 s, the corresponding adjustment function is switched off by the driver-side front seat adjustment control unit with memory 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.

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Rear easy entry

Additional function requirements

- Circuit 15 ON and relevant vehicle door open or

- Circuit 15R ON

- circuit 15 ON and vehicle speed  5 km/h

 If, during the process, the function conditions are canceled, the head restraint movement continues until it is completed. Furthermore, the function is only started when no abort conditions are pending.

 The precondition for the function is that the head restraint adjustment was normalized at the upper stop.

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Folding front seat forward

Pulling the backrest release handle mechanically releases the backrest, which can then be folded forward.

When releasing, the driver seat backrest release microswitch (S91/3) is actuated and read in by the driver-side front seat adjustment control unit with memory (N32/1).

Then the head restraint up/down motor (M27m4) is actuated by the driver-side front seat adjustment control unit with memory and the head restraint moves to the downstop to prevent a collision with the headliner when folding the backrest forward.

When folding the backrest forward, the driver seat height release microswitch (S91/4) is actuated.

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Folding front seat backward

If the backrest in the folded-forward position is folded back into the starting position, the driver seat backrest release microswitch closes. The backrest locks mechanically in the folded back end position. Pushing the backrest further back operates the driver seat height release microswitch.

Pressing the driver seat height release microswitch enables the driver-side front seat adjustment control unit with memory to recognize whether the backrest is correctly locked and send a signal, where applicable, to the instrument cluster (A1) to display a corresponding warning indicator.

After locking the backrest and the height adjuster, the head restraint returns to its original position again.

Abort conditions

- Seat adjustment is activated

- Hall sensor for head restraint up/down motor defective.