Active Head Restraint - Operation

OPERATION

The Active Head Restraint (AHR) units are deployed by a signal generated by the Occupant Restraint Controller (ORC) through the first row right and left solenoid and ground signal circuits. The ORC logic monitors inputs from the front impact sensors as well as electronic message inputs received over the Controller Area Network (CAN) data bus to determine when the appropriate conditions exist to send a deployment signal to both AHR units. When the ORC detects an impact pulse of sufficient magnitude originating from the rear of the vehicle, while any transmission gear is selected except Reverse (R), the ORC sends the deployment signals.

When the ORC sends the proper electrical deployment signal to the solenoid of the AHR unit, the solenoid releases the AHR latch. When the AHR latch is released, the tension of the spring-loaded linkage within the AHR mechanically drives the AHR pad through a short, slightly forward and upward arc to the final deployed position. Deployment of the AHR reduces the space between the back of the head of the seat occupant and the head restraint pad. Closing this space supports the head of the seat occupant during a low speed rear impact collision event and is important in reducing or eliminating potentially debilitating cervical (also known as whiplash) injuries.

The ORC monitors the condition of the AHR unit circuits, and will illuminate the airbag indicator in the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) and store a Diagnostic Trouble Code (DTC) for any fault that is detected.

The hard wired circuits between the AHR units and the ORC may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the AHR units or the electronic controls or communication between other modules and devices that provide some features of the Supplemental Restraint System (SRS). The most reliable, efficient, and accurate means to diagnose the AHR units or the electronic controls and communication related to AHR unit operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.