Part 2

Fig.6 Airbag Control Module:

AIRBAG CONTROL MODULE
The Airbag Control Module (ACM) is also sometimes referred to as the Occupant Restraint Controller (ORC). The ACM is concealed underneath the center floor console, where it is secured by four screws to a stamped steel mounting bracket welded onto the top of the floor panel transmission tunnel just forward of the park brake mechanism in the passenger compartment of the vehicle.

Concealed within a hollow in the center of the die cast aluminum ACM housing is the electronic circuitry of the ACM 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 ACM housing with four screws to enclose and protect the internal electronic circuitry and components. A printed label on the top of the ACM 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 forward side of the ACM housing. These two receptacles connect the ACM 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. For vehicles equipped with the optional side curtain airbags, both ACM connector receptacles are black in color and the ACM contains a second bi-directional safing sensor for the side airbags. For vehicles not equipped with the optional side curtain airbags, the ACM connector receptacles are both gray.

The impact sensor and safing sensor internal to the ACM are calibrated for the specific vehicle, and are only serviced as a unit with the ACM. The ACM cannot be repaired or adjusted and, if damaged or faulty it must be replaced.

The microprocessor in the Airbag Control Module (ACM) contains the supplemental restraint system logic circuits and controls all of the supplemental restraint system components. The ACM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the DRB III 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 ElectroMechanical Instrument Cluster (EMIC) 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. (Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES/COMMUNICATION - OPERATION).

The ACM microprocessor continuously monitors all of the supplemental restraint system electrical circuits to determine the system readiness. If the ACM detects a monitored system fault, it sets an active and stored Diagnostic Trouble Code (DTC) and sends electronic messages to the EMIC 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 ACM. For some DTCs, if a fault does not recur for a number of ignition cycles, the ACM will automatically erase the stored DTC. For other internal faults, the stored DTC is latched forever.

The ACM receives battery current through two circuits, on a fused ignition switch output (RUN) circuit through a fuse in the Junction Block (JB), and on a fused ignition switch output (start-run) circuit through a second fuse in the JB. The ACM is grounded through a ground circuit and take out of the instrument panel floor wire harness. This take out has a single eyelet terminal connector secured by a nut to a ground stud located behind the ACM mount on the floor panel transmission tunnel. These connections allow the ACM to be operational whenever the ignition switch is in the Start or ON positions. The ACM 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 airbags 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 ACM during an impact.

Two sensors are contained within the ACM, an electronic impact sensor and a safing sensor. The ACM also monitors inputs from two remote front impact sensors located on brackets on the inboard 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. On models equipped with optional side curtain airbags, the ACM also monitors inputs from two remote side impact sensors located near the base of both the left and right inner B-pillars to control the deployment of the side curtain airbag units.

The safing sensor is an electronic accelerometer sensor within the ACM that provides an additional logic input to the ACM microprocessor. The safing sensor is used to verify the need for an airbag 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. The ACM also monitors a Hall effect-type seat belt switch located in the buckle of each front seat belt to determine whether the seatbelts are buckled, and provides an input to the EMIC over the PCI data bus to control the seatbelt indicator operation based upon the status of the driver side front seat belt switch. Vehicles with the optional side curtain airbags feature a second safing sensor within the ACM to provide confirmation to the ACM of side impact forces. This second safing sensor is a bi-directional unit that detects impact forces from either side of the vehicle.

Pre-programmed decision algorithms in the ACM 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. The ACM also determines the level of front airbag deployment force required for each front seating position based upon the status of the two seat belt switch inputs and the severity of the monitored impact. When the programmed conditions are met, the ACM sends the proper electrical signals to deploy the multistage dual front airbags at the programmed force levels, and to deploy either side curtain airbag.

The hard wired inputs and outputs for the ACM may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the ACM, the PCI data bus network, or the electronic message inputs to and outputs from the ACM. The most reliable, efficient, and accurate means to diagnose the ACM, the PCI data bus network, and the electronic message inputs to and outputs from the ACM requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.

Fig.10 Child Tether Anchors - North America:

Fig.11 Child Tether Anchors - Rest-Of-World:

CHILD TETHER ANCHOR
All vehicles are equipped with fixed-position, child seat tether anchors. Vehicles manufactured for sale in North America have two stamped steel child tether anchor brackets, one secured with a screw to each outboard end of the inner liftgate opening header at the rear of the passenger compartment. These child tether anchors are concealed behind a removable molded plastic cap that snaps into a bezel located in the headliner over each anchor bracket position. Vehicles manufactured for sale in Rest-Of-World (ROW) markets have two anchors that are integral to the back of the right rear seat back panel, and one that is integral to the left rear seat back panel. The North American child seat tether anchor brackets are available for separate service replacement. The ROW child seat tether anchors cannot be adjusted or repaired and, if faulty or damaged, they must be replaced as a unit with the rear seat back panel.

See the owner's manual in the vehicle glove box for more information on the proper use of the factory-installed child seat tether anchors.

Fig.13 Clockspring (Upper View):

Fig.14 Clockspring (Lower View):

CLOCKSPRING
The clockspring assembly is secured with two screws to the multi-function switch mounting housing near the top of the steering column behind the steering wheel. The clockspring consists of a flat, round molded plastic case with a stubby tail that hangs below the steering column and contains two connector receptacles that face toward the instrument panel. Within the plastic housing is a spool-like molded plastic rotor with a large exposed hub. The upper surface of the rotor hub has a large center hole, two large flats, an index hole, two short pigtail wires with connectors, and two connector receptacles that face toward the steering wheel.

The lower surface of the rotor hub has three pins, two round and one oblong. These pins index the clockspring to the turn signal cancel cam unit in the multi-function switch mounting housing. Within the plastic case and wound around the rotor spool is a long ribbon-like tape that consists of several thin copper wire leads sandwiched between two thin plastic membranes. The outer end of the tape terminates at the connector receptacles that face the instrument panel, while the inner end of the tape terminates at the pigtail wires and connector receptacles on the hub of the clockspring rotor that face the steering wheel.

Service replacement clocksprings are shipped precentered and with a molded plastic locking pin installed. The locking pin secures the centered clockspring rotor to the clockspring case during shipment and handling, but must be removed from the clockspring after it and the multi-function switch mounting housing are installed on the steering column. (Refer to ELECTRICAL/RESTRAINTS/CLOCKSPRING - STANDARD PROCEDURE - CLOCKSPRING CENTERING).

The clockspring cannot be repaired. If the clockspring is faulty damaged, or if the driver airbag has been deployed, the clockspring must be replaced.

The clockspring is a mechanical electrical circuit component that is used to provide continuous electrical continuity between the fixed instrument panel wire harness and the electrical components mounted on or in the rotating steering wheel. On this model the rotating electrical components include the driver airbag, the horn switch, the speed control switches, and the remote radio switches, if the vehicle is so equipped. The clockspring case is positioned and secured to the multi-function switch mounting housing on the upper steering column housing by two screws. The two connector receptacles on the tail of the fixed clockspring case connect the clockspring to the vehicle electrical system through two take outs with connectors from the instrument panel wire harness. The clockspring rotor is movable and is keyed to the hub of the steering wheel by two large flats that are molded into the rotor hub. The three pins (two round and one oblong) on the lower surface of the clockspring rotor hub engage and index the clockspring rotor to the turn signal cancel cam. The turn signal cancel cam is integral to the multi-function switch mounting housing and is keyed to the upper steering column shaft. Two short, yellow-sleeved pigtail wires on the upper surface of the clockspring rotor connect the clockspring to the driver airbag, while a steering wheel wire harness connects the two connector receptacles on the upper surface of the clockspring rotor to the horn switch, the two speed control switches, and the remote radio switches on vehicles that are so equipped.

Like the clockspring in a timepiece, the clockspring tape has travel limits and can be damaged by being wound too tightly during full stop-to-stop steering wheel rotation. To prevent this from occurring, the clockspring must be centered when it is installed on the steering column. Centering the clockspring indexes the clockspring tape to the movable steering components so that the tape can operate within its designed travel limits. However, if the clockspring is removed from the steering column or if the steering shaft is disconnected from the steering gear, the clockspring spool can change position relative to the movable steering components and must be re-centered following completion of the service or the tape may be damaged. Service replacement clocksprings are shipped pre-centered and with a locking pin installed. This locking pin should not be removed until the clockspring has been installed on the steering column. If the locking pin is removed before the clockspring is installed on a steering column, the clockspring centering procedure must be performed. (Refer to ELECTRICAL/RESTRAINTS/CLOCKSPRING - STANDARD PROCEDURE - CLOCKSPRING CENTERING).