Air Bag Systems: Description and Operation

The Air Bag-Supplemental Restraint System (SRS AIRBAG) is designed to supplement the seat belt to help reduce the risk or severity of injury to the driver and passenger by activating and deploying the driver and passenger side airbag in certain frontal or side collisions.

The SRSCM type equipped with this model is HAE-3.
HAE-3 is applied for DAB + 2BPT, DAB + PAB + 2BPT, DAB + PAB + 2BPT + 2FSAB.

The SRS (Airbag) consists of:
A driver side airbag module located in the center of the steering wheel, which contains the folded cushion and an inflator unit.
A passenger side airbag module located in the passenger side crash pad contains the folded cushion assembled with inflator unit.
Side airbag modules located in the driver and passenger seat which contain the folded cushion and an inflator unit.
SRSCM located on the floor under the heater core which monitors the system.
An accelerometer which senses the vehicle deceleration.
A spring interconnection (clock spring) located within the steering column system wiring and wiring connector.
A knee bolster located under the steering column.
The impact sensing function of the SRSCM is carried out by electronic accelerometer that continuously measure the vehicle's acceleration and delivers a corresponding signal through amplifying and filtering circuity to the microprocessor.

Deployment of the airbag is designed to occur in frontal or near-frontal or side impacts of moderate of severe force. Only authorized service personnel should do work on or around the SRS components. Those service personnel should read this information carefully before doing any such work. Extreme care must be used when servicing the SRS to avoid injury to the service personnel (by inadvertent deployment of the airbag) or the driver (by render the SRS inoperative).

The SRS airbag system has sophisticate electrical and electronic components, therefore the airbag operating components should be handled very carefully.

SRSCM (Supplemental Restraint System Control Module)
SRSCM determines to deploy the airbag module by sensing the frontal and side impact sensed by the sensor built in SRSCM.
DC/DC convertor: The power supply DC/DC converters include a step-up and step-down converter, which provides the firing voltage for two firing circuits and the internal operating voltage. If the internal operating voltage falls below a defined threshold, a reset is executed.
Arming sensor/safing sensor: The arming/safing sensor built in the airbag firing circuit has the function of arming the airbag circuit under all required deployment condition and maintaining the airbag firing circuits unarmed under normal driving conditions. The safing sensor is a dual-contact electromechanical switch which closes if it experiences a deceleration exceeding a specified threshold.
Back-up power: The SRSCM reserves the energy supply to provide deployment energy for a short second when the vehicle voltage is low or if lost in a vehicle frontal crash.

Malfunction detection: The SRSCM continuously monitors the current SRS operation status while the ignition key is turned on and detects the malfunction of the system. The malfunction can be displayed in the form of diagnostic trouble code using Scan tool (Hi-scan).
MIL (Malfunction Indication Lamp) notification: If any fault is detected, the SRSCM sends signal to the indicator lamp on the cluster to warn the vehicle driver. The MIL indicator is the key to driver notification of SRS faults. Verify lamp and SRSCM operation by flashing 6 times when the ignition switch is first turned on.
Malfunction recording: Once a fault occurred in the system SRSCM records the fault in the memory in the form of DTC and the DTC can only be erased with the scan tool.
Data link connector: The SRSCM memory stored data is accessed through the OBD-II Data Link Connector (DLC) using a scan tool. The DLC is located underneath the driver side crash pad.
After firing the airbags once, the SRSCM cannot be used again and must be replaced.
Crash output:The crash output is used to control an external device such as door control module in case of a crash event.
The crash output is specified as follows:
* The crash output is open-collector type switch logic output with 500 mA of sine current and its output impedance is 100 ohms.
* The crash output is switched to ground for 200 ms after the crash detected.