SRS Airbag Construction and Operation – Center airbag sensor assembly


The center airbag sensor assembly is mounted on the center floor under the instrument panel and consists of diagnosis circuit, ignition control circuit, deceleration sensor, safing sensor, etc.
Front airbags and seat belt pretensioners circuit
Side and curtain shield airbags circuit (When the safing sensor is stored in the side airbag sensor and curtain shield airbag sensor)
(1)Diagnosis circuit
This circuit constantly diagnoses the system for any malfunction. When a malfunction is detected, it lights up or blinks the SRS warning light to warn the driver.
(2)Ignition control circuit
The ignition control circuit performs a prescribed calculation based on the signal output by the deceleration sensors of the airbag sensor assembly and front airbag sensor assembly. If these calculated values are larger than a predetermined value, it activates the ignition operation.

(3)Deceleration sensor
Based on the deceleration of the vehicle that occurs during a frontal collision, the distortion that is created in the sensor is converted into an electric signal. This signal is a linear representation of the deceleration rate.
(4)Safing sensor
The safing sensor, which is built in the center airbag sensor assembly, turns on if a deceleration force that is higher than a predetermined value is applied to the safing sensor as a result of a collision.
(5)Back-up power source
The back-up power source consists of a power supply capacitor and a DC-DC converter. In case of a power system failure during a collision, the power supply capacitor discharges and supplies electric power to the system. The DC-DC converter is a boosting transformer when the battery voltage drops below a certain level.
(6)Memory circuit
When a malfunction is detected by the diagnosis circuit, it is coded and stored in this memory circuit.
The codes can be retrieved later to identify the location of the malfunction and provide quicker troubleshooting. Depending on the model, this memory circuit is either the type in which the memory contents are erased when power is interrupted, or the type in which the memory contents are retained even if the power is interrupted.
In some models, center airbag sensor assembly transmits the signal that deploys the airbags to the body ECU and unlocks all the doors, which makes it easier for the occupants to get out of the vehicle or to be rescued in case of an accident.
At this time, center airbag sensor assembly also transmits signal to the engine ECU to stop the fuel pump.

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