Air Bag Systems: Description and Operation

SRS System Description

SRS Components ('00-05 models)

Airbags

The SRS is a safety device which, when used with the seat belt, is designed to help protect the driver and passenger in a frontal impact exceeding a certain set limit. The system consists of the SRS unit, including a safing sensor and an impact sensor (A), the cable reel (B), the driver's airbag (C) and the passenger's airbag (D).

Seat Belt Tensioners

The seat belt tensioners (E) is linked with the SRS airbags to further increase the effectiveness of the seat belt. In a front-end collision, the tensioner instantly retracts the belt firmly to secure the occupants in their seats.

SRS Operation ('00-05 models)

The main circuit in the SRS unit senses and analyzes the force of impact and, if necessary, ignites the inflator charges. If the battery voltage is too low or power is disconnected due to impact, the voltage regulator and the back-up power circuit respectively will keep voltage at a constant level.

For the SRS to operate:

(1) The impact sensor must activate and send electronic signals to the microprocessor.

(2) The microprocessor must compute the signals and trigger the airbag inflators (and seat belt tensioners).

(3) The triggered inflators must ignite and deploy the airbags (and activate the tensioners).

Self-diagnostic System

A self-diagnostic circuit is built into the SRS unit; when the ignition switch is turned to ON (II), the SRS indicator comes on and goes off after about 6 seconds if the SRS is operating normally.

If the indicator does not come on, or does not go off after 6 seconds, or comes on while driving, it indicates an abnormality in the SRS. The SRS must be inspected and repaired as soon as possible.

For better serviceability, the SRS unit memory stores a DTCs related to the cause of the malfunction, and the unit is connected to the data link connector (DLC). This information can be read with the HDS when it is connected to the DLC. Initial Inspection and Diagnostic Overview

NOTE: Before you disconnect the negative cable from the battery for troubleshooting, review Battery Terminal Disconnection and Reconnection. Procedures

SRS Components ('06-09 models)

Airbags

The SRS is a safety device which, when used with the seat belt, is designed to help protect the driver and passenger in a frontal impact exceeding a certain set limit. The system consists of the SRS unit, including safing sensor and impact sensor (A), the cable reel (B), the driver's airbag (C), the passenger's airbag (D), seat belt tensioners (E), and front impact sensors (F).

Since the driver's and passenger's airbags use the same sensors, both normally inflate at the same time. However, it is possible for only one airbag to inflate. This can occur when collision severity is near the threshold for airbag. In such case, the SRS system will only deploy airbags when the protection provided by the seat belt is insufficient.

Passenger's Weight Sensors

The passenger's weight sensor unit (G) is under the passenger's seat along with the passenger's weight sensors (H). The passenger's weight sensors detect the weight on the seat, and send the information to the passenger's weight sensor unit. If the total weight is about 65 lbs (30 kg) or less, the passenger's weight sensor unit sends a signal to the SRS unit to prevent the passenger's airbag from deploying. When the passenger's airbag is disabled, the passenger airbag cutoff indicator on the center panel comes on to alert the driver that the passenger's airbag will not deploy in a front-end collision.

Driver's Seat Position Sensor

The driver's seat position sensor (I) is under the driver's seat on the left side. When the driver's seat is moved to its full forward position, the deployment of the driver's airbag is moderated to decrease its force of impact during a front-end collision.

Passenger Airbag Cutoff Indicator ('06-09 models)

The indicator comes on when the weight of the passenger is about 65 lbs (30 kg) or less. This indicates the passenger's front airbag is off and will not deploy. The front airbag is shut off to reduce the chance of airbag-caused injuries.

SRS Operation ('06-09 models)

The main circuit in the SRS unit senses and judges the force of impact and, if necessary, ignites the inflator charges. If battery voltage is too low or power is disconnected due to the impact, the voltage regulator and the back-up power circuit will keep voltage at a constant level.

For the SRS to operate:

Seat Belt Tensioners

(1) A front impact sensor must activate and send electric signals to the microprocessor.

(2) The microprocessor must compute the signals and trigger the tensioners.

(3) The charges must ignite and deploy the tensioners.

Driver's and Passenger's Airbag(s)

(1) A front impact sensor must activate and send electric signals to the microprocessor.

(2) The microprocessor must compute the signals, and trigger the airbag inflator(s).

(3) The triggered inflators must ignite and deploy the airbags.

*: GRN wire be substituted for the wire color in this table.

SRS Unit Inputs and Outputs at Connector A (28P) ('06-09 models)

*: BLU, GRN, GRY, ORN, or BRN wires may be substituted for the wire colors in this table.

SRS Unit Inputs and Outputs at Connector B (28P) ('06-09 models)

*: BLU, GRN, GRY, ORN, or BRN wires may be substituted for the wire colors in this table.