Air Bag Control Module: Description and Operation

The SRS airbag system has sophisticated 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 converter: The DC/DC convertors of the power supply includes a step up and a step down converter, which provides the firing voltage for six 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.
- 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 is erased only by Scan tool.
- Data link connector: The SRSCM memory stored data are linked through this connector located at the underneath of driver side crash pad to the external output device such as Scan tool.
- 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 which will unlock the doors in case of a crash event.
The crash output is specified as follows: 0 - 200 micro-amps in OFF mode and 200 mA in ON mode. In case of the unlock command the switch is closed for 200 ms.