Occupant Restraint Controller - Operation

OPERATION

The microprocessor in the Occupant Restraint Controller (ORC) contains the Supplemental Restraint System (SRS) logic circuits and controls all of the SRS components. The ORC 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 used for control of the airbag indicator in the Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) and for SRS diagnosis and testing through the 16-way data link connector located on the driver side lower edge of the instrument panel.

The ORC microprocessor continuously monitors all of the SRS electrical circuits to determine the system readiness. If the ORC detects a monitored system fault, it sets an active and stored Diagnostic Trouble Code (DTC) and sends electronic messages to the IC over the CAN data bus to turn ON the airbag indicator. An active fault only remains for the duration of the fault, or in some cases for the duration of the current ignition cycle, while a stored fault causes a DTC to be stored in memory by the ORC. For some DTCs, if a fault does not recur for a number of ignition cycles, the ORC will automatically erase the stored DTC. For other internal faults, the stored DTC is latched forever.

The ORC receives battery current through two circuits; a fused ignition switch output (run) circuit through a fuse in the Body Control Module (BCM) (also known as the Common Body Controller/CBC) and a fused ignition switch output (run-start) circuit through a second fuse in the BCM. The ORC receives ground through a ground circuit and take out of the instrument panel wire harness that is secured by a ground screw to the body sheet metal. These connections allow the ORC to be operational whenever the ignition switch is in the START or ON positions.

The ORC 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 SRS components for up to one second following a battery disconnect or failure. The purpose of the capacitor is to provide backup SRS protection in case there is a loss of battery current supply to the ORC during an impact.

Various sensors within the ORC are continuously monitored by the ORC logic. These internal sensors, along with several external impact sensor inputs allow the ORC to determine both the severity of an impact and to verify the necessity for deployment of any SRS components. Two remote front impact sensors are located on the back of the right and left vertical members of the radiator support near the front of the vehicle. The electronic impact sensors are accelerometers that sense the rate of vehicle deceleration, which provides verification of the direction and severity of an impact.

The ORC also monitors inputs from an internal rollover sensor, seat track position sensors, seat belt switches and six additional remote side impact sensors located on the left and right front door module carriers, on the right and left lower B-pillars and on the right and left C-pillars near the belt line to control deployment of the side curtain airbag units and seat (also known as pelvic and thorax) airbags. On vehicles so equipped, the ORC also uses the passenger side seat belt switch input along with an input from the Occupant Detection Sensor (ODS) in the passenger front seat cushion to support the passenger belt alert feature, and will send electronic messages to the IC to illuminate the seat belt indicator when appropriate.

The impact sensors within the ORC are electronic accelerometer sensors that provide an additional logic input to the ORC microprocessor. These sensors are used to verify the need for a SRS component deployment by detecting impact energy of a lesser magnitude than that of the primary electronic impact sensors, and must exceed a safing threshold in order for the SRS components to deploy. On vehicles equipped with side curtain airbags or seat airbags, a separate impact sensor within the ORC provides confirmation to the ORC microprocessor of side impact forces. This separate sensor is a bi-directional unit that detects impact forces from either side of the vehicle.

Pre-programmed decision algorithms in the ORC microprocessor determine when the deceleration rate as signaled by the impact sensors indicate an impact that is severe enough to require SRS protection and, based upon the severity of the monitored impact, determines the level of front airbag deployment force required for each front seating position. When the programmed conditions are met, the ORC sends the proper electrical signals to deploy the dual multistage front airbags at the programmed force levels, the front seat belt tensioners and, if the vehicle is so equipped, the seat airbags and either side curtain airbag unit.

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

PEDESTRIAN PROTECTION SYSTEM

In vehicles so equipped, a microcontroller within the ORC also contains the Electronic Pedestrian Protection (EPP) system (also known as the PedPro or the Active Hood System) logic circuits. The EPP system logic of the ORC continuously monitors the three dedicated EPP acceleration-type electronic impact sensors located behind the front bumper area of the fascia 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 ORC also monitors electronic ignition status, vehicle speed and ambient temperature message inputs received from other electronic modules over the CAN data bus. The EPP system logic of the ORC uses a pre-programmed decision algorithm to analyze all of these inputs, which allows the ORC 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 ORC sends the proper electrical signals to deploy the actuators. As a safing function, the ORC requires confirming sensor inputs from at least two of the three EPP impact sensors before it will issue a deployment signal.

The ORC 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 ORC during an impact event.

An Event Data Recorder (EDR) within the ORC stores EPP near-deployment event records. The ORC microcontroller continuously monitors all of the EPP system electrical circuits to determine the system readiness. If the ORC detects a monitored system fault, it logs an active DTC. The ORC also stores a DTC after it has been resolved. When the ORC 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 EPP inputs and outputs for 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 ORC 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 ORC 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.