Restraints

OPERATION

The microcontroller within the Electronic Pedestrian Protection Module (EPPM) contains the Electronic Pedestrian Protection (EPP) system (also known as the PedPro or the Active Hood System) logic circuits. The EPPM receives battery current through a fused ignition switch output (run-start) circuit and a fuse in the Power Distribution Center (PDC). The EPPM receives ground through two ground circuits and a take out of the body wire harness that is secured by a ground screw to the body sheet metal. These connections allow the EPPM to be operational whenever the ignition switch is in the START or ON positions.

The EPPM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the diagnostic scan tool using the Controller Area Network (CAN) data bus. This method of communication is also used by the Occupant Restraint Controller (ORC) to monitor the EPPM and for EPP system diagnosis and testing through the 16-way data link connector located on the driver side lower edge of the instrument panel.

The EPPM logic continuously monitors the three dedicated EPP acceleration-type electronic impact sensors located on the top of the front bumper support beam at the front of the vehicle. The impact sensors are accelerometers that sense the rate of vehicle deceleration, which provides verification of the direction and severity of an impact. The EPPM also monitors electronic ignition status, vehicle speed and ambient temperature message inputs received from other electronic modules over the CAN data bus. The EPPM uses a pre-programmed decision algorithm to analyze all of these inputs, which allows the EPPM to determine both the type and severity of an impact.

When the deceleration rate as signaled by the impact sensors indicate an impact that requires the deployment of the pyrotechnic EPP actuator located on each active hood hinge at the rear corners of the hood panel and all other programmed conditions are met, the EPPM sends the proper electrical signals to deploy the actuators. As a safing function, the EPPM requires confirming sensor inputs from at least two of the three EPP impact sensors before it will issue a deployment signal.

The EPPM also contains an energy-storage capacitor. When the ignition switch is in the START or ON positions, this capacitor is continually being charged with enough electrical energy to deploy the active hood hinge actuators for up to one second following a battery disconnect or failure. The purpose of the capacitor is to provide backup EPP system protection in case there is a loss of battery current supply to the EPPM during an impact event.

An Event Data Recorder (EDR) within the EPPM stores both deployment event and near-deployment event records. The near-deployment records can be overwritten, the deployment records cannot. After three deployment records have been stored, a Deployment Data Record Full Diagnostic Trouble Code (DTC) is logged. Once the Deployment Data Record Full DTC is logged, the EPPM and both active hood hinges must be replaced with new units.

The EPPM microcontroller continuously monitors all of the EPP system electrical circuits to determine the system readiness. If the EPPM detects a monitored system fault, it logs an active DTC. The EPPM also stores a DTC after it has been resolved. The ORC continually monitors the EPPM and, when it detects that the EPPM has logged a DTC, it sends electronic request messages over the CAN data bus to the Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) to turn ON the airbag indicator.

The hard wired inputs and outputs for the EPPM 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 EPPM or the electronic controls or communication between other modules and devices that provide features of the EPP system. The most reliable, efficient, and accurate means to diagnose the EPPM or the electronic controls and communication related to EPP system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.