Pedestrian Protection System - Operation

PEDESTRIAN PROTECTION SYSTEM

In the event of a frontal vehicle impact, the Electronic Pedestrian Protection (EPP) system (also known as the PedPro or the Active Hood System) components are designed and intended to enhance the protection for pedestrians from the hard components found just beneath the hood of the vehicle within the engine compartment. The EPP system has three acceleration-type impact sensors located in the front bumper area of the vehicle, a microcontroller-based Occupant Restraint Controller (ORC) located within the passenger compartment of the vehicle that also serves as the EPP system controller and an active hood hinge with a pyrotechnic-type actuator at each rear corner of the hood panel.

The impact sensors continually transmit sensor data to the ORC that give an indication of the forces of gravity (G force) upon the sensors. The ORC also receives electronic message inputs over the Controller Area Network (CAN) data bus indicating the ignition status, vehicle speed and ambient temperature. If the vehicle has a collision, the ORC uses algorithms to analyze all of the input data to determine whether to deploy the hood. If the algorithm makes a deployment decision and that the vehicle speed is between 22 kilometers-per-hour (14 miles-per-hour) and 52 kilometers-per-hour (32 miles-per-hour), then the ORC will send electrical signals to deploy the actuators on the active hood hinges.

When the micro gas generator in each actuator is energized, it produces a large quantity of expanding gas. The expanding gas moves a piston within the actuator that pushes upward against the hood bracket of the active hood hinge. The force of the actuator on the hinge bracket creates a lever action that shears a rivet between the hood bracket and the mid-strap of both hood hinges, allowing the actuators to lift the rear of the hood at the hinges. Lifting the rear of the hood in this manner provides additional clearance between the hood and the hard components found within the engine compartment.

Each active hood hinge functions normally during routine opening and closing of the hood. However, upon active hood hinge deployment the rear of the hood is lifted to a predetermined height, which is controlled by an up-stop pin on the hinge bracket that is engaged within a slotted hole in the mid-strap of each hinge.

During a frontal pedestrian impact, the purpose of the pedestrian bar (also known as the leg catcher) that supports the lower front fascia is to reduce the severity of leg injuries and to position the pedestrian onto the hood of the vehicle rather than onto the pavement. These goals are both intended to reduce the severity and debilitating nature of potential pedestrian injuries. It should be noted that the pedestrian bar must be inspected and replaced if visually damaged following any frontal vehicle impact, regardless of whether or how the active hood is deployed.

The EPP system electrical circuits are continuously monitored and controlled by the ORC microcontroller. If the ORC detects a problem it stores a fault code or Diagnostic Trouble Code (DTC) in its memory circuit and sends an electronic request message to the Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) to illuminate the airbag indicator. The airbag indicator may be turned ON or OFF by the ORC to indicate a problem in either the Supplemental Restraint System (SRS) or the EPP system electrical circuits.

The hard wired circuits between components related to the EPP system may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

However, conventional diagnostic methods will not prove conclusive in the diagnosis of the EPP system or the electronic controls or communication between other modules and devices that provide inputs to the ORC. The most reliable, efficient, and accurate means to diagnose the ORC or the electronic controls and communication related to EPP system operation, as well as the retrieval or erasure of a DTC requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.