Town Car V8-4.6L SOHC VIN W (1999)
Air Bag Control Module: Description and Operation
The Restraints Control Module (RCM) performs the following functions:
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signals the inflators to deploy the air bags in the event of a deployable crash.
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monitors the air bag Supplemental Restraint System (SRS) for faults.
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illuminates the air bag indicator if a fault is detected.
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flashes the air bag indicator to indicate the Lamp Fault Code (LFC) detected.
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communicates through the Data Link Connector (DLC) the current or historical Diagnostic Trouble Codes (DTCs).
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signals the Lighting Control Module (LCM) to activate a chime if the air bag indicator is not available and another SRS fault exists.
NOTE: The safety sensor is internal to the RCM and is not serviced separately.
The RCM monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the RUN Position, the RCM will illuminate the air bag
indicator located in the instrument cluster.
When the ignition is cycled (turned off and then on), the air bag indicator will flash the two-digit LFC. The air bag indicator will flash the LFC five
times, then it will remain illuminated for the rest of the key cycle. The RCM will also communicate the current and historical DTCs through the DLC,
using the New Generation Star (NGS) tester. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the
LCM to activate an audible chime. The chime is a series of five sets of five tone bursts. If the chime is heard, the SRS and the air bag indicator require
repair.
LFCs are prioritized. If two or more faults occur at the same time, the fault having the highest priority will be displayed first. After that fault has been
corrected, the next highest priority fault will be displayed.
The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the air bags in the event that the ignition circuit is
damaged in a collision before the safing and air bag sensors close. The backup power supply will deplete its stored energy approximately one minute
after the battery ground cable is disconnected.
