When the ignition switch is turned to ON, the sensing and diagnostic module (SDM) will perform a turn-on test to diagnose critical malfunctions within the SDM itself.

In case of the 1st stage air bag inflation by a vehicle collision, the SDM maintains the warning lamp ON and all the air bag systems including the SDM, air bag module, and wiring should be replaced.

The history of the 1st stage air bag inflation or the belt pretensioner explosion is in the SDM.