3rd seat row folding function - GF91.29-P-2018GZ

MODEL 164.8 with CODE (845) 3rd seat row, electrically folding

Illustrated on model 164.8

Fig 1: Identifying 3rd Seat Row Folding Function - Illustrated On Model 164.8

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function conditions

Circuit 30
Speed <= 12 km/h
Rear-end door or right rear door open and
Folding backrest in park position switch detected

Actuating mechanism

The operation of the folding backrest switches is read in by the folding rear bench seat control unit.

The folding rear bench seat control unit checks whether the backrest is locked or unlocked. If the backrest is locked, the relevant backrest release unit is actuated. If the backrest is unlocked, the folding rear bench seat control unit actuates the relevant folding backrest motor.

If the backrest is unlocked when the folding backrest switch is operated (unlocking switch closed), the relevant folding backrest motor is actuated immediately.

If the folding backrest switches for the left and right seats are operated simultaneously, the right seat is actuated first. After the maximum actuation time (approx. 0.4 s) of the unlocking motor in the right seat unlocking unit, the left seat is actuated.

The unlocking switches and the unlocking motors are integrated in the left backrest release unit and the right backrest release unit.

The end position of the folded seat is recorded by a limit position switch in the left backrest release unit and the right backrest release unit. This limit position switch can be used to record two possible positions: "seat raised" and "seat lowered".

End of operation

The actuation of the folding backrest motors stops when:

the respective folding backrest switch is released, or
the backrest is detected as locked (unlocking switch open) and the time difference between the opening of the unlocking switch and the end of backrest motor actuation is too great or
the maximum actuation time of the folding backrest motor has been reached (18 s), or
blocking is detected.

Locking monitoring

The unlocking switches in the backrest release unit are used to monitor the backrests. If a backrest is detected as unlocked, the rear seat control unit transmits a message to the instrument cluster. The following messages are displayed on the instrument cluster:

LEFT BACKREST OF 3RD SEAT ROW NOT LOCKED
or
RIGHT BACKREST OF 3RD SEAT ROW NOT LOCKED

Behavior with several switch operations

If the other switch is operated for the same seat after operating a folding backrest switch, the first function is aborted. The second adjusting function does not start. Adjustment does not continue until it has been detected that both switches are in the park position.

Stuck switch detection:

Switch signal > 20 s

If a switch is detected as stuck, the relevant channel is blocked. Functions requested by the stuck switch will not be performed until the park position has been detected.

Blockage detection

In order to prevent damage to the seat mechanism, the actuation time of the folding backrest motors is limited. This is done by evaluating the Hall sensor signal in the motor concerned. If the signal width is greater than the blocking detection time (can be adjusted via diagnosis), blocked status is detected and the relevant folding backrest motor is shut off.

After blocking has been detected in a particular direction, motorized adjustment can take place again by actuating in the same direction. The folding backrest motors are also protected from overheating using a thermo switch.

Block diagram of electric seat adjustment (ESA [ESV])

With code 232 Electrically adjustable front passenger seat with memory, with code 275 Memory package (driver seat, steering column, mirrors)

GF91.29-P-0004-03GZ