For 1990-2009 cars

### Circuit Description

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.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1620 ECU Performance

### Conditions for Running the DTC

Ignition voltage is within the normal operating voltage range.

### Conditions for Setting the DTC

The SDM does not implement diagnostic operation. In case of the above, the wiring harness of the SDM should be inspected before replacing the SDM.

### Action Taken When the DTC Sets

The SDM commands the AIR BAG indicator ON.

### Conditions for Clearing the DTC

The condition responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used.

Warning: Refer to Sensing and Diagnostic Module Voltage after Ignition is Turned Off Warning in the Preface section.

Warning: Refer to Sensing and Diagnostic Module Handling Warning in the Preface section.