SCMB Passenger Power Head Restraint Operation

The power head restraint assembly contains a seat headrest motor (up/down) and a seat head restraint forward/rearward motor. The passenger seat control switch communicates over a LIN to the SCMB. When the SCMB receives the input from the seat control switch, the SCMB provides power the appropriate head restraint motor until the input is removed. The motor circuits are normally grounded through the SCMB. The SCMB internally switches the appropriate circuit from ground to voltage to operate the motors.

If the SCMB loses the signal from any of the motor position sensors, the affected head restraint motor operates in jog mode. Jog mode allows limited operation of the affected head restraint motor using the seat control switch. When the seat control switch is operated in jog mode, the head restraint moves in the desired direction for one second, then stops. The seat control switch must be released, then pressed again in order to move the head restraint for an additional second. Jog mode is an indication that there is a head restraint motor sensor fault. If the head restraint is operating in jog mode, a DTC sets in the SCMB.

As the passenger seat head restraint is adjusted, the SCMB monitors the motor position sensors to record the current seat position. The SCMB removes voltage from the motor upon termination of the seat control switch input or if the SCMB does not detect movement from the motor while monitoring the position sensor during a memory recall operation.