Component Definitions
"AIR BAG" WARNING LAMP
Ignition voltage is applied to the "AIR BAG" warning lamp when the ignition switch is at the ON or START positions. The SDM controls the lamp by providing ground with a lamp driver. The "AIR BAG" warning lamp is used in the SRS to do the following:
1. Verify lamp and SDM operation by flashing SEVEN (7) times when the ignition switch is first turned "ON".
2. Warn the vehicle driver of SRS electrical system malfunctions which could potentially affect the operation of the SRS. These malfunctions could result in non- deployment in case of a frontal crash or deployment for conditions less severe than intended.
The "AIR BAG " warning lamp is the key to driver notification of SRS malfunctions.
SRS Coil Assembly
The SRS coil assembly consists of two current carrying coils. This is attached to the steering column and allow rotation of the steering wheel while maintaining continuous contact of the driver deployment loop to the driver air bag assembly.
There is a shorting clip on the yellow 3-way connector near the base of steering column which connects the SRS coil to the SRS wiring harness.
The shorting clip shorts to the SRS coil and driver air bag assembly when the yellow 3-way connector is disconnected. The circuit to the driver air bag assembly is shorted in this way to help prevent unwanted deployment of the air bag when servicing the steering column or other SRS components.
Air Bag Assemblies
The air bag assembly consist of an inflatable air bag assembly and an inflator (a canister of gas - generating material and an initiating device). When the vehicle is in a frontal crash of sufficient force.
The SDM causes current flows through the deployment loops. Current passing through the inflator ignites the material in the air bag assembly. The gas produced from this reaction rapidly inflates the air bag assembly.
There is a shorting clip on the driver air bag assembly connector which connects the SRS coil assembly. The shorting clip shorts across the driver air bag assembly circuits when driver air bag assembly connector is disconnected.
The circuit to the driver air bag assembly is shorted in this way to help prevent unwanted deployment of the air bag when servicing the driver air bag assembly, the steering column or other SRS components.
Sensing and Diagnostic Module (SDM)
Sensing and Diagnostic Module (SDM) is designed to perform the following functions in the SRS:
1. Energy Reserve - The SDM maintains 24-Volt Loop Reserve(24VLR) energy supply to provide deployment energy when ignition voltage is lost in a frontal crash.
2. Frontal Crash Detection - The SDM monitors vehicle velocity changes to detect frontal crashes which are severe enough to warrant deployment.
3. Air Bag Deployment - When a frontal crash of sufficient force is detected, the SDM will cause enough current to flow through the air bag assembly to deploy the air bag.
4. Malfunction Detection - The SDM performs diagnostic monitoring of SRS electrical components and sets a diagnostic trouble code when a malfunction is detected.
5. Frontal Crash Recording - The SDM records information regarding SRS status during frontal crash.
6. Malfunction Diagnosis - The SDM display SRS diagnostic trouble codes and system status information through the use of a scan tool.
7. Driver Notification - The SDM warns the vehicle driver of SRS malfunctions by controlling the "Air Bag" warning lamp.
STEERING COLUMN
The steering column absorbs energy and is designed to compress in a frontal crash to decrease the chance of injury to the driver.
Knee Bolsterds
The knee bolsters are used to absorb energy to protecting knees and control the forward movements of the vehicle's front seat occupants during a frontal crash, by limiting leg movements.