Active Head Restraint
Active Head Restraint
Description
Active Head Restraint (AHR) units are available equipment for both front seating positions in this vehicle. One AHR unit is located atop each front seat back - 2 -. An AHR can be readily distinguished from a non-active head restraint by the two-piece construction used for an AHR. The forward-facing pad - 1 - consists of a molded reinforced plastic convex form covered with a dense foam pad and is trimmed in a material coordinated with the other soft trim on the seat. The rearward-facing surface is equipped with a hard molded plastic trim cover - 3 - that matches the other hard trim on the seat.
Located between the pad and the trim cover are the support structure of the AHR and both the mechanical and electrical components of the unit. The support structure includes a molded plastic carrier that is securely clamped to a U-shaped, bright-plated metal tube, the legs of which form the two visible posts - 4 - that are used to secure the unit in the two plastic guide sleeves - 5 - located at the top of the seat back frame. These posts feature numerous notches that engage spring-loaded detents integral to the plastic guide sleeves which are used for manually adjusting the vertical height of the AHR unit to properly fit the seat occupant.
The mechanical components of the AHR include the linkage that permits the lower part of the pad to be tilted forward or rearward for comfort as well as the linkage that articulates the pad during deployment, a pair of heavy wire springs, a caliper-type latch mechanism and the latch striker. The single electrical component of the AHR unit is a latch-release solenoid and the pigtail wire that connects the solenoid to the vehicle electrical system. The pigtail wire and connector are routed through the center of one of the support posts and down through the guide sleeve into the interior of the seat back, where it is connected to a dedicated take out and connector of the seat wire harness.
The AHR cannot be repaired. If damaged or ineffective, it must be replaced with a new unit. However, unlike many other Supplemental Restraint System (SRS) components, following an AHR deployment, if no visible damage to the unit is observed it can usually be successfully reset and reused. Refer to => [ Active Head Restraint Reset Procedure ] Active Head Restraint Reset Procedure.
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.