SRS System Description - SRS Unit(Except Touring)
System Diagram
- Power supply circuit (booster circuit, backup power supply): Provided to maintain power when battery voltage is low or in case of power supply damage due to a collision.
- Front impact G sensor and Side impact G sensor: Detects impact to the SRS unit as acceleration, and converts it to electrical signal.
- Rollover judgment circuit: Predicts an impending rollover using signals such as the one from the G sensor located inside of the SRS unit. Based on the rollover judgment made and the seat belt buckle switch status, the circuit determines to whether the side airbags and the side curtain airbags should deploy or not.
- Microprocessor: An impact decision algorithm decides whether or not the collision signal warrants deployment of the airbags or the tensioners.
- Diagnostic circuit: Performs self-diagnosis to determine whether system abnormalities are present. If an abnormality is detected, the SRS indicator in the gauge control module turns on.
- Non-volatile memory: Records fault conditions. The SRS memories are not erased even if the 12 volt battery terminal is disconnected.
- Communication circuit: Circuit for outputting or deleting memory contents.
When airbags or tensioners are to be deployed, a large amount of current passes through the SRS unit. After the airbags and tensioners are deployed, the interior of the SRS unit is damaged, and must be replaced.
Automatic Short Circuit Mechanism of SRS Unit Connectors
When the SRS unit connectors are disconnected from the SRS unit, the automatic short-circuit mechanism in the connectors creates short-circuits to prevent accidental deployment of an airbag or tensioner. This automatic short-circuit mechanism is configured in such a way that the respective deployment side circuits (adjacent terminal) are short-circuited when the connector is disconnected.
Connected condition
Disconnected condition
Electrical Terminal Fit Detection System
The connectors connected to the SRS unit are equipped with a terminal that short-circuits the fit detection terminals with each other. If the connectors are properly connected, the fit detection terminals are short-circuited to each other, and the SRS unit detects the fitting of the various connectors. If the SRS unit activates when a fitting is not detected, poor terminal fitting is judged and a DTC is stored.
Rollover Detection
A sensor integrated into the SRS unit performs rollover detection. The sensor detects the degree of vehicle roll and converts it to an electrical signal. If the SRS unit determines that a vehicle rollover is occurring, one or both side curtain airbags and seat belt tensioners will be deployed depending on the direction and number of rollover events.