Air Bag Control Module: Description and Operation
SRSCMThe SRS airbag system has sophisticated electrical and electronic components. Therefore the airbag operating components should be handled very carefully.
SRSCM (Supplement Restraint System Control Module)
The SRSCM will deploy the airbag modules by sensing the frontal impact sensed by the sensor built in to the SRSCM.
1. DC/DC convertor: The DC/DC converter in the power supply includes a step-up and a step-down converter, which provides the firing voltage for four firing circuits and the internal operating voltage. If the internal operating voltage falls below a defined threshold, a reset is executed.
2. Arming sensor/safing sensor : The arming/safing sensor built in to the airbag firing circuit has the function of arming the airbag circuit under all required deployment conditions and maintaining the airbag firing circuits unarmed under normal driving conditions. The safing sensor is a dual-contact electromechanical switch that closes if it experiences a deceleration exceeding a specified threshold.
3. Back-up power: The SRSCM reserves an energy reserve to provide deployment energy for a short period when the vehicle voltage is low or if lost in a vehicle frontal crash.
4. Malfunction detection : The SRSCM continuously monitors SRS operating status while the ignition key is turned on and detects possible malfunctions in the system. The malfunction can be displayed in the form of a diagnostic trouble codes using the Hi-Scan Pro.
5. MIL (Malfunction Indication Lamp) notification: If any fault is detected, the SRSCM sends a signal to the indicator lamp on the instrument cluster to warn the vehicle driver.
The MIL indicator is the key item in notifying the driver of SRS faults. It verifies lamp and SRSCM operation by flashing 6 times when the ignition switch is first turned on.
6. Malfunction recording : Once a fault occurs in the system, the SRSCM records the fault in memory in the form of a DTC, which can only be erased by the Hi-Scan Pro.
7. Data link connector: SRSCM memory stored is linked through this connector located underneath the driver side crash pad to an external output device such as the Hi-Scan Pro.
8. What if only BPT's deploy.
9. Crash output
The crash Output is used to unlock the doors in case of a crash. The crash output is : 0-200 micro A in OFF mode and 200mA in ON mode. During the unlock command, the switch is closed for 200 mS.
SRS HARNESS
The SRS harness is wrapped in a yellow tube to be discriminated from other system harnesses. A shorting bar is included inside the wiring connectors of DAB, PAB, SAB and BPT inflator side. The shorting bar shorts the current flow the DAB, PAB, SAB and BPT module circuits when the connectors are disconnected. The circuits to the inflator module are shorted in this way to help prevent unwanted deployment of the airbag when servicing the airbag module.
SRSCM INDEPENDENT LAMP ACTIVATION
The SRS malfunction indicator lamp (MIL) is located in the cluster giving information of SRS operating conditions by control signals from the SRSCM.
There are certain fault conditions in which the SRSCM (SRS Control Module) cannot function and thus cannot control the operation of the lamp. In these cases, the lamp is directly activated by appropriate circuitry that operates independently of the SRSCM, follows:
1. Loss of ignition voltage supply to the SRSCM : lamp turned on continuously.
2. Loss of internal operating voltage: lamp turned on continuously.
3. SRSCM not connected: lamp turned on through shorting bar in wiring harness connector.
MIL Operating Method:
MIL OPERATING METHOD