See Figure 1
The air bag system used on Celica is referred to as Supplemental Restraint System (SRS). The SRS provides additional protection for the driver and front passenger, if a forward collision of sufficient force is encountered. The SRS assists the normal seatbelt restraining system by deploying an air bag, via the steering column.
The center air bag sensor is the heart of the SRS. It consists of safing sensors, ignition control and drive circuit, diagnosis circuit, etc. The center air bag sensor receives signals from the air bag crash sensors and determines whether the air bag must be activated or not. The center air bag sensor is also used to diagnose system malfunctions.
The air bag warning light circuit is equipped with an electrical connection check mechanism which detects when the connector to the center air bag sensor assembly is not properly connected.
All connectors in the air bag system are colored yellow. These connectors use gold-plated terminals with twin-lock mechanism. This design assures positive locking; there-by, preventing the terminals from coming apart.
When the ignition switch is turn to the ON or ACC position, the air bag warning lamp will turned on for approximately 6 seconds. If no malfunctions are detected in the system, after the 6 second period have elapse, the warning light will go off.
The safing sensors are designed to go on at a lower deceleration rate than the front or center air bag sensor. When the vehicle is involved in a frontal collision, the shock is great enough to overcome the predetermine level of the front or center air bag sensor. When a safing sensor and a front air bag sensor and/or the center air bag sensor go on simultaneously, it causes the squib of the air bag to ignite and the air bag is deployed automatically. The inflated bag breaks open the steering wheel pad.
After air bag deployment have occurred, the gas is discharged through the discharge holes provided behind the bag. The bag become deflated as a result.
The connector of the air bag contains a short spring plate, which provides an activation prevention mechanism. When the connector is disconnected, the short spring plate automatically connects the power source and grounding terminals of the inflator module (squib).
Front Air Bag Sensors
See Figure 1
A front air bag sensor is mounted inside each of the front fenders. The sensor unit is basically a mechanical switch. When the sensor detects a deceleration force above a predetermined level in a collision, the contacts in the sensor close, sending a signal to the center air bag sensor assembly. The sensor cannot be disassembled. If the front fenders on the vehicle are damaged in any way, do a visual check of the sensors even if the air bag is not deployed. Inspect for:
Center Air Bag Sensor
See Figure 1
The center air bag sensor is mounted on the floor inside the console box. The air bag sensor determines whether or not the air bag should be deployed and is also used to diagnose system malfunction.Spiral Cable
See Figure 1
The spiral cable, part of the combination switch, is used as an electrical joint from the vehicle body to the steering wheel. The spiral cable is referred to as a clock spring.Drivers Air Bag
See Figure 1
The drivers air bag, located in the steering wheel pad, contains a gas generant which will rapidly inflate the bag in a case of frontal collision.Passengers Air Bag
See Figure 1
The inflator and bag of the SRS are located in the front of the passengers air bag assembly and can not be disassembled. The air bag will inflate only when the sensor instructs it to do so.SRS Warning Lamp
See Figure 2
The air bag SRS warning lamp, located on the combination meter, is used to alert the driver of any malfunctions within the air bag system. In normal operating conditions when the ignition switch is turned to the ON or ACC , the light goes on for about 6 seconds and then goes off.
All connectors in the SRS are colored yellow to distinguish them from the other connectors. These connectors have special functions are specifically designed for the SRS. These connectors use durable gold-platted terminals.TWIN TERMINAL LOCKING MECHANISM
Each connector has a two-piece construction consisting of a housing and a spacer. This secures the locking of the terminal by two locking devices (the spacer and lance) to prevent terminals from coming out.ACTIVATION SPRING PREVENTION MECHANISM
See Figure 3
Each connector contains a short spring plate. When the connector is disconnected, the short spring plate automatically attaches the power source and grounding terminals of the squib.
This mechanism is designed to electrically check if the connectors are attached correctly and completely. The connection check mechanism is designed so that the connection detection pin connects with the diagnosis terminals when the housing lock is in the locked position.CONNECTOR TWIN LOCK MECHANISM
See Figure 4
With this mechanism connectors (male and female) are locked by two devices to increase the connection reliability. If the primary lock is incomplete, ribs interfere and prevent the secondary lock from engaging.
See Figure 5
DISARMING THE SYSTEM
Work must be started only after 90 seconds from the time the ignition switch is turned to the LOCK position and the negative battery cable has been disconnected. The SRS is equipped with a back-up power source so that if work is started within 90 seconds of disconnecting the negative battery cable, the SRS may deploy. When the negative terminal cable is disconnected from the battery, memory of the clock and radio will be canceled. Before you start working, make a note of the contents memorized by the audio memory system. When you have finished work, reset the audio systems as before and adjust the clock. To avoid erasing the memory of each system, never use a back-up power supply from outside the vehicle.
ARMING THE SYSTEM
Reconnect the negative battery cable and perform the airbag warning light check by turning to the ON or ACC position, the air bag warning lamp will turned on for approximately 6 seconds. If no malfunctions are detected in the system, after the 6 second period has elapsed, the warning light will go off.