Air Bag: Description and Operation

Airbag Warning Lamp




The instrument cluster contains an airbag warning indicator and sensing and diagnostic module (SDM). The SDM performs a turn-on test when the ignition is turned on. The SDM flashes the airbag indicator seven times by supplying an intermittent ground to the indicator lamp circuit. After flashing seven times, the airbag indicator will turn off if no more malfunctions have been detected.

If the SDM has detected malfunctions in the internal and external circuits, which could potentially affect the operation of the supplemental inflatable restraints (SIR), the airbag indicator stays on. Some malfunctions could result in non-deployment when necessary or deployment under conditions which would not normally result in deployment. When the SDM is not properly attached to its connector, the airbag circuit is shorted to ground because there is a shorting bar in the SDM electrical connector. The shorting bar is disengaged when proper connection is made, but if a poor connection exists the SDM connector supplied a ground to the airbag indicator independently of the SDM connector, and the airbag indicator turns on.