OBD port DODGE RAM 1999 Service Repair Manual

protective cover is fitted to front of air bag module bearing the SRS
air bag logo. Air bag module contains air bag cushion, inflator and
supporting components. Air bag module is a sealed unit and is not
serviceable. The module inflator assembly produces nitrogen gas to
fill air bag cushion when a small amount of current from ACM is
applied to the ignitor assembly. Gas pressure builds and discharges
from inflator through a diffuser and screen assembly, forcing steering
wheel cover to burst along its seams until air bag is fully inflated.
Once air bag cushion is fully inflated, gas escapes from bag through
vents, away from driver.
Passenger-Side
Air bag module is mounted to instrument panel mounting
bracket. Module is covered by a protective door bearing the SRS air
bag logo. When supplied an electrical signal, inflator will discharge
argon gas directly into air bag. When air bag inflates, protective
door will pivot aside allowing air bag to deploy.
AIR BAG CONTROL MODULE (ACM)
ACM is located under instrument panel, on transmission
tunnel. Impact sensor, energy reserve capacitor and On-Board
Diagnostics (OBD) are an integral part of ACM. ACM monitors critical
input and output circuits within air bag system, ensuring they are
operating correctly. Some circuits are tested continuously; others are
checked only under certain conditions. ACM provides information about
air bag system through AIR BAG warning light and Data Link Connector
(DLC). When diagnostic trouble code (fault message) is stored, AIR B\
AG
warning light will be activated for 12 seconds or more.
DATA LINK CONNECTOR (DLC)
DLC is located under left side of instrument panel, left of
steering column. DLC is used to access SRS on-board diagnostics.
CLOCKSPRING
Clockspring connects air bag module to steering column
wiring, completing air bag system circuit. See Fig. 1. Inside
clockspring is a flat, ribbon-like tape of conductive material, which
winds and unwinds with steering wheel movement. Clockspring is the
most fragile part of air bag system. Clockspring must be centered
properly to allow 1 1/2 steering wheel turns in either direction. If
clockspring is not centered properly, it can break from stretching or
fatigue.
Fig. 1: Identifying Clockspring Assembly
Courtesy of DaimlerChrysler Corp.