Air Bag Control Module: Description and Operation

ORC - Location:

The Occupant Restraint Controller (ORC) is also sometimes referred to as the Airbag Control Module (ACM). The ORC is concealed beneath the instrument panel center stack, just in front of the floor console, where it is secured by three screws to a stamped steel mounting bracket welded onto the top of the floor tunnel in the passenger compartment of the vehicle. Concealed within a hollow in the center of the die cast aluminum ORC housing is the electronic circuitry of the ORC which includes a microprocessor, an electronic impact sensor, an electronic safing sensor, and an energy storage capacitor. A stamped metal cover plate is secured to the bottom of the ORC housing with four screws to enclose and protect the internal electronic circuitry and components.

An arrow printed on the label on the top of the ORC housing provides a visual verification of the proper orientation of the unit, and should always be pointed toward the front of the vehicle. Two molded plastic electrical connector receptacles exit the right side of the ORC housing. These two receptacles connect the ORC to the vehicle electrical system through a dedicated take out and connector of the instrument panel wire harness, and a dedicated take out and connector of the airbag overlay wire harness. The ORC contains a second bi-directional safing sensor for the curtain airbags.

The impact sensor and safing sensor internal to the ORC are calibrated for the specific vehicle, and are only serviced as a unit with the ORC. The ORC cannot be repaired or adjusted and, if damaged or faulty, it must be replaced. Refer to the proper Body Diagnostic Procedures manual for diagnosis and testing.

The microprocessor in the Occupant Restraint Controller (ORC) contains the supplemental restraint system logic circuits and controls all of the supplemental restraint system components. The ORC uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the DRBIII(R) scan tool using the Programmable Communications Interface (PCI) data bus network. This method of communication is used for control of the airbag indicator in the Instrument Cluster and for supplemental restraint system 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 supplemental restraint system 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 cluster over the PCI data bus to turn on the airbag indicator. An active fault only remains for the duration of the fault or in some cases the duration of the current ignition switch cycle, while a stored fault causes a DTC to be stored in memory by the ORC. For some DTC's, 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; on a fused ignition switch output (RUN) circuit through a fuse in the Integrated Power Module (IPM), and on a fused ignition switch output (START/ RUN) circuit through a second fuse in the IPM. The ORC is grounded through a ground circuit and take out of the instrument panel floor wire harness. 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 supplemental restraint components for up to one second following a battery disconnect or failure. The purpose of the capacitor is to provide backup supplemental restraint system protection in case there is a loss of battery current supply to the ORC during an impact.

Two sensors are contained within the ORC, an electronic impact sensor and a safing sensor. The ORC also monitors inputs from two remote front impact sensors located on brackets on the outboard sides 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 provide verification of the direction and severity of an impact. The ORC also monitors inputs from six additional remote side impact sensors, located in the B and C-pillars and over the rear wheelhouse, to control the deployment of the curtain airbag units.

The safing sensor is an electronic accelerometer sensor within the ORC that provides an additional logic input to the ORC microprocessor. The safing sensor is used to verify the need for a supplemental restraint 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 airbags to deploy. Because of the side curtain airbags feature, a second safing sensor within the ORC is to provide confirmation to the ORC of side impact forces. This second safing sensor is a bidirectional 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 and the safing sensors indicate an impact that is severe enough to require supplemental restraint system 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 and; if the vehicle is so equipped, knee blocker airbag, and the front seat belt tensioners and either curtain airbag.