GF91.16-P-0001FL Retractable Rear Head Restraints (RHR (KAF)) Function

GF91.16-P-0001FL Retractable Rear Head Restraints (RHR [KAF]) Function

General function requirements
- No overvoltage or undervoltage

Retractable rear head restraints, general
By lowering the rear head restraints, the driver is able to create unimpeded visibility through the rear window as needed.

Raising the rear head restraints is only possible by hand.

The retractable rear head restraints system comprises the following partial functions:
^ Function sequence for head restraint lowering mechanism
^ Function sequence for temperature protection
^ Function sequence: Error storage

Function sequence for head restraint lowering mechanism
The rear head restraints can be lowered as follows:
- Pressing the rear head restraint button (N72/1s4) in the upper control panel control unit (N72/1)
- Unlocking the rear seat backrest (with code (275) Memory package for electrically adjustable front seats and code (287) Through-loading feature)

When lowering, the mechanical components of the rear head restraints are unlocked by the following motors:
- Left rear head restraint seat adjustment motor (M53/1)
- Right rear head restraint seat adjustment motor (M53/2)
- Center rear head restraint seat adjustment motor (M53/3)

The rear head restraints are lowered by means of their own dead weight.

Following activation, there is a t = 3 s break before the head restraint seat adjustment motor can be actuated again.

The head restraint lowering mechanism consists of the following partial functions:
^ Function sequence for head restraint lowering mechanism via rear head restraint button
^ Function sequence for head restraint lowering mechanism by unlocking the rear seat backrest (with code (275)
Memory package for electrically adjustable front seats and code (287) Through-loading feature)

Additional function requirements for head restraint lowering mechanism via rear head restraint button
^ Circuit 15 On
^ Rear backrest not folded over (with code (275) Memory package for electrically adjustable front seats and code (287) Through-loading feature)

The status of circuit 15 is sent by the electronic ignition lock control unit (N73) via the interior CAN (CAN B)

Function sequence for head restraint lowering mechanism via rear head restraint button
The front SAM control unit reads in the status of the rear head restraint button via instrument panel LIN (LIN 1) and sends the request for retractable rear head restraints to the rear SAM control unit with fuse and relay module (N10/2) via interior CAN.

The rear SAM control unit then actuates the rear head restraint seat adjustment motors for t = 600 ms.

Function sequence for head restraint lowering mechanism by unlocking the rear seat backrest (with code (275) Memory package for electrically adjustable front seats and code (287) Through-loading feature)

The unlocking of the rear seat backrest is recorded by the left rear backrest lock switch (S54/7) or the right rear backrest lock switch (S54/8). The respective rear backrest lock switch sends the information regarding whether the backrest is locked or unlocked to the rear SAM control unit. The rear SAM control unit then actuates the rear head restraint seat adjustment motors.

If during this actuation the status of the left rear backrest lock switch and the right rear backrest lock switch is no longer recognized, the actuation is ended.

Function sequence for temperature protection
As protection against overheating of the rear head restraint seat adjustment motors, a counter is increased by 1 following actuation and after t = 7 s the value of the counter is decreased by 1, irrespective of further actuations. As long as the counter value lies within the range of 0 to 20 (default), actuations are permissible. If the counter reaches the maximum value, the next actuation is only possible after t = 7 s.

Function sequence: error storage
The following errors are recognized in the system and saved in the fault memory:
- Malfunction due to short circuit to ground
- Malfunction due to short circuit to positive or an open circuit

These errors are recognized after the rear head restraint seat adjustment motor is actuated 10 times. As a result, the head restraints in the rear are not lowered. The error is marked as a text message in the instrument cluster.