Air Bag Supplemental Restraint System (SRS) (Description and Operation)

The air bag supplemental restraint system (SRS) is designed to provide increased collision protection for front seat occupants in addition to that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantages of the SRS.

The air bag supplemental restraint system (SRS) components are shown in the following illustration.

Air Bag Supplemental Restraint System (SRS) Components

Driver Air Bag Module

The driver air bag module:

• is installed as an assembly.
• is mounted in the center of the steering wheel.

Clockspring

The clockspring:

• is mounted on the steering column, behind the steering wheel.
• provides a continuous electrical path from the restraints control module (RCM) to the driver air bag.

Passenger Air Bag Module

The passenger air bag module:

• is installed as an assembly.
• is mounted in the RH side of the instrument panel.

Restraints Control Module (RCM)

The restraints control module (RCM) performs the following functions:

• signals the inflators to deploy the air bags in the event of a deployable crash.
• monitors the air bag supplemental restraint system (SRS) for faults.
• illuminates the air bag indicator if a fault is detected.
• flashes the air bag indicator to indicate the lamp fault code (LFC) detected.
• communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).
• signals the generic electronic module (GEM) to activate a chime if the air bag indicator is not available and another SRS fault exists.

NOTE: The safing sensor is internal to the RCM and is not repaired 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 begin its prove out sequence. During prove out the air bag indicator will illuminate for six seconds, go off for two seconds and then, if a system fault exists, 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 a scan tool. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the GEM 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. 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 determine that deployment is required. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected.

Electrical System

The electrical system that supports the air bag supplemental restraint system (SRS):

• is powered from the battery through the ignition circuit.
• provides the electrical path from the restraints control module (RCM) to the air bag modules.
• provides the electrical path from the RCM to the air bag indicator.
• provides the electrical path from the RCM to the data link connector (DLC).
• provides the electrical path from the RCM to the generic electronic module (GEM).

Sensor

WARNING: The restraints control module (RCM) orientation is critical for proper system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, the RCM must be replaced whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.

The SRS contains two sensors which are integral to the RCM. The RCM is mounted on the center tunnel under the instrument panel.

• Pinpoint Test A: The Air Bag Warning Indicator Is Illuminated Continuously - RCM Disconnected, Inoperative or Lost/Low Ignition Feed
• Pinpoint Test B: LFC 21/DTC B1921 - RCM Bracket Ground Resistance High
• Pinpoint Test C: LFC 29/DTC C1414 - Incorrect Vehicle Identification Code
• Pinpoint Test D: LFC 15/DTC B 1887- Driver Air Bag Circuit Shorted to Ground
• Pinpoint Test E: LFC 15/DTC B1916 - Driver Air Bag Circuit Shorted to Battery or Ignition
• Pinpoint Test F: LFC 16/DTC B1888 - Passenger Air Bag Circuit Shorted to Ground
• Pinpoint Test G: LFC 16/DTC B1925 - Passenger Air Bag Circuit Shorted to Battery or Ignition
• Pinpoint Test H: LFC 32/DTC B1932 - Driver Air Bag Circuit Resistance High
• Pinpoint Test I: LFC 33/DTC B1933 - Passenger Air Bag Circuit Resistance High
• Pinpoint Test J: LFC 34/DTC B1934 - Driver Air Bag Circuit Resistance Low
• Pinpoint Test K: LFC 35/DTC B1935 - Passenger Air Bag Circuit Resistance Low
• Pinpoint Test L: B1892 - Air Bag Tone Warning Indicator Circuit Shorted to Ground or Open
• Pinpoint Test M: DTC B1891 - Air Bag Tone Warning Indicator Circuit Shorted to Battery or Ignition
• Pinpoint Test N: DTC B1869 - Air Bag Indicator Inoperative
• Pinpoint Test O: DTC B1870 - Air Bag Indicator Shorted to Battery
• Pinpoint Test P: No Communication With The Restraints Control Module