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Airbag (SRS)

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Since its launch, the NSX was equipped with a driver's airbag. As of 1993 a passenger airbag and seat belt tensioners were added. The system is of rather simple design with the ECU containing an acceleration sensor that works together with two dash sensors and fires the airbag and seat tensioners upon front impact.

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SRS ECU under the centre console (JDM)
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SRS ECU (1997)
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SRS top PCB (1997)


Due to it's simple nature, the SRS ECU does not record crash data or the like. It's more or less an analogue circuit device.
To ensure proper detection as well as firing, the system monitors both the acceleration sensor inside the ECU as well as the dash sensors. If one or both of the dash sensors are activated together with the internal acceleration sensor, all airbags and seat tensioners are activated.

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Start-up, monitoring and fire sequence

Since >1993 the ECU needs to check and fire more activators. To do so, more and larger backup-power supply capacitors as well as a second PCB has been added to the housing. The number of sensors and the detection mechanism is identical, though.

Honda Legend SRS ECUs are utilizing the same sensor and detection mechanism.

The first character on the model number sticker defines whether the unit is from a Right Hand Drive (RHD) or Left Hand Drive (LHD) vehicle. N__ indicates an RHD unit and A__ an LHD unit. Although the housing is different between LHD and RHD, the inside is the same.

Fault Detection
The SRS ECU is of a rather simple design. Its most important task is to charge-up the emergency power supply capacitors and check all attached sensors (internal and dash) as well as all activators (airbag and seat tensioner).

Any issues are displayed on the gauge cluster via the SRS warning light. The warning indicator lights up upon ignition-on and turns off within six seconds. If it stays lit this indicates an issue with the SRS system. Due to it's simple nature, the SRS ECU does not store or provide any fault codes.

Known Issues
Similar to many other ECUs in the car, the SRS ECU suffers from capacitor leakage. A typical symptom is the warning light staying lit because of a blown SRS fuse and the fuse keeps blowing until the ECU is disconnected.
Due to the difficulties of acquiring replacement units a preventive capacitor replacement is highly recommended.

Updated 12-02-2021 at 06:48 PM by Heineken

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