Restraints and Safety Systems: Description and Operation
System DescriptionSRS Components
Airbags
The SRS is a safety device which, when used with the seat belt, is designed to help protect the driver and front 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 front passenger's airbag (D), side airbags (E), side curtain airbags (L), seat belt tensioners (I), front impact sensors (J), side impact sensors (first) (F), and side impact sensors (second) (K).
Since the driver's and front 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 the severity of a collision is at the margin, or threshold, that the SRS unit determines whether or not the airbags will deploy. In such cases, the seat belt will provide sufficient protection, and the supplemental protection offered by the airbag would be minimal.
Front Passenger's Weight Sensors
The front passenger's weight sensor unit (M) is under the front passenger's seat along with the weight sensors (N). The weight sensors detect the weight on the seat, and send the information to the front passenger's weight sensor unit. If the total weight is about 65 lbs (30 kg) or less, the front 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 front passenger's airbag will not deploy in a front-end collision.
Driver's Seat Position Sensor
The driver's seat position sensor (O) 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.
Rear Safing Sensor
The rear safing sensor (P) is located under the middle of the rear seat. The rear safing sensor performs the same basic function as the safing sensor in the SRS unit. It measures sideways G force, such as the force the vehicle would receive in a side collision in the rear, and sends that information to the SRS unit. The SRS unit uses that information, and the information from the second side impact sensors to determine the side that is impacted and the force. If the threshold is met, the SRS unit deploys the side airbag, the side curtain airbag and the seat belt tensioner on that side.
Side Airbags
The side airbags (E) are in each front seat-back. They help protect the upper torso of the driver or front seat passenger during a moderate to severe side impact. Side impact sensors (first) (F) in each door sill, side impact sensors (second) (K) in each rear door sill, rear safing sensor under the rear seat (P), and the SRS unit safing sensor detect such an impact and instantly inflate the driver's or the passenger's side airbag. Only one side airbag will deploy during a side impact. If the impact is on the passenger's side, the passenger's side airbag will deploy even if there is no passenger.
Side Curtain Airbags
The side curtain airbags (L) are in each side of the roof. They help protect the head of the driver, front passenger, and passengers in the rear outer seats during a moderate to severe side impact. Side impact sensors (first) (F) in each front door sill, side impact sensors (second) (K) in each rear door sill, rear safing sensor (P) under the rear seat, and the SRS unit detect such an impact and instantly inflate the driver's or the passenger's side curtain airbag. A side impact causes the side curtain airbag and the side airbag on the impacted side to deploy at the same time.
Seat Belt Tensioners
The seat belt tensioners are linked with the SRS airbags to further increase the effectiveness of the seat belt. In a front-end collision, the tensioners instantly retract the belt firmly to secure the driver and front passenger in their seats.
OPDS
The side airbag system also includes an occupant position detection system (OPDS). This system consists of sensors (G) and a OPDS unit (H) in the front passenger's seat-back. The OPDS unit sends occupant height and position data to the SRS unit. If the OPDS unit determines that the front passenger is of small stature (for example, a child) or the front passenger is leaning into the side airbag deployment path, the SRS unit will automatically disable the passenger's side airbag. The SRS unit will also disable the airbag when the OPDS detects certain objects on the seat. When the side airbag is disabled, the side airbag cutoff indicator on the instrument panel alerts the driver that the passenger's side airbag will not deploy in a side impact. When the object is removed, or the passenger sits upright, the side airbag cutoff indicator will go off after a few seconds, alerting the driver that the passenger's side airbag will deploy in a side impact.
Side Airbag Cutoff Indicator/OPDS Operation
The indicator comes on if the front passenger's seat is occupied by a small adult or child who is leaning into the deployment path, or an object (grocery bag, briefcase, purse, etc.) is in the seat. This indicates the passenger's side airbag is off and will not deploy; there is no problem with the side airbag. If the passenger sits upright or moves to another seat, or you remove the object from the seat, the light should go off. There will be some delay between the occupant's repositioning, and when the indicator will turn on or off.
Passenger Airbag Cutoff Indicator
The indicator comes on if the weight of the front passenger is about 65 lbs 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
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 or side impact sensor must activate and send electric signals to the microprocessor.
2. The microprocessor must compute the signals and send them to the tensioners.
3. The charges must ignite and deploy the tensioners.
Driver's and Front 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 send them to the airbag inflator(s).
3. The inflators that received signals must ignite and deploy the airbags.
Side Airbag(s)
1. A side impact sensor must activate and send electric signals to the microprocessor.
2. The microprocessor must compute the signals and send them to the side airbag inflator(s). However, the microprocessor cute off the signals to the front passenger's side airbag if the SRS unit determines that the front passenger's head is in the deployment path of the side airbag.
3. The inflator that received the signal must ignite and deploy the side airbag.
Side Curtain Airbag(s)
1. Side impact sensors must activate and send electrical signals to the microprocessor.
2. The microprocessor must compute the signals and send them to the side curtain airbag and side airbag inflator(s).
3 The inflator that received the signals must ignite and deploy the side curtain airbag and side airbag at the same time.
Self-diagnosis System
A self-diagnosis circuit is built into the SRS unit; when the ignition switch is turned ON (II), the SRS indicator comes on and goes off after about 6 seconds if the system is operating normally. If the indicator does not come on, or does not go off after 6 seconds, or if it comes on while driving, it indicates an abnormality in the system. The system must be inspected and repaired as soon as possible.
For better serviceability, the SRS unit memory stores a DTC that relates 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 (16P).
NOTE: Before you disconnect the negative cable from the battery for troubleshooting, make sure you have the anti-theft code for the audio and the navigation system. Write down the frequencies for the audio presets.
E-pretensioner ('06 Model)
When at a risk of a collision, the e-pretensioner system, working with the collision mitigation braking system (CMBS), retracts the driver's and front passenger's seat belt several times slightly to provide a tactile warming to the driver. And when a collision is imminent, the e-pretensioner system retracts the seat belt tightly to help reduce injury from the impact. The e-pretensioner system also works when the driver brakes hard and the brake assist system is turned on.
CMBS and E-pretensioner Operation ('06 Model)
Approaching a vehicle ahead: When driving, the millimeter wave radar detects a vehicle ahead, and the system provides audible and visual warnings if it detects a risk of collision.
Closing on a vehicle ahead: The system applies light braking, and increases seat belt tension slightly to provide a tactile warning to the driver. The front passenger does not feel the tactile warning.
Collision unavoidable: The system active strong braking, and securely tightens both the driver's and passenger's seat belts to help reduce injury caused by the impact.
E-pretensioner ('06 Model)
The mechanical portion of the e-pretensioner consists of the motor and the gear systems. When the collision mitigation brake or the brake assist system signals are input, the motor in the retractor system is driven to rewind or retract. If the system judges that the driving situation is safe, the tension on the seat belts is released. The e-pretensioners used in conjunction with the conventional tensioners.
E-pretensioner Unit ('06 Model)
The e-pretensioner unit operates the motor-driving controls based on F-CAN data it receives from the adaptive cruise control unit, VSA modulator-control unit, and the PCM. Also the e-pretensioner unit receives seat belt buckle switch signals from the SRS unit by an interactive communication function. The e-pretensioner unit has a self-diagnostic function, and if it detects a malfunction, it sends its information to the SRS unit. The SRS indicator is then turned on by the SRS unit.