For 1990-2009 cars

### Circuit Description

When you first turn the ignition switch to the ON position, the inflatable restraint Sensing and Diagnostic Module (SDM) performs tests to diagnose critical malfunctions within itself. The SDM internally monitors the air bag sensor, the safing sensor, the drive circuit, the diagnosis circuit and the ignition control. When system voltage is applied to the SDM, it performs the Primary Check followed by the Constant Check. If a malfunction is detected, the SDM will set a DTC and illuminate the AIR BAG warning lamp.

### Conditions for Setting the DTC

The SDM detects an overcharge condition.

The SDM detects an internal malfunction.

### Action Taken When the DTC Sets

• | The SDM sets a Diagnostic Trouble Code.

• | The SDM turns ON the AIR BAG warning lamp.

### Conditions for Clearing the DTC

All DTCs are cleared with each ignition cycle.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the SIR Diagnostic System Check performed? | -- | Go to Step 2 | Go to SIR Diagnostic System Check
2 |

1. Turn the ignition switch to the LOCK position
2. Turn the ignition switch to the ACC or ON position and wait 20 seconds.
3. Read the SIR DTCs.

Is DTC 31 flashed?

--

Go to Step 3

Go to SIR Diagnostic System Check

3 | Is DTC 31 the only DTC flashed? | -- | Go to Step 5 | Go to Step 4
4 | Diagnose the DTCs from the lowest to the highest. Are the other DTCs diagnosed and the repairs made? | -- | Go to SIR Diagnostic System Check | --
5 |

1. Turn the ignition switch to the LOCK position.
2. Disable the SIR system. Refer to Disabling the SIR System .
3. Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .

Has the SDM been replaced?

--

Go to Step 6

--

6 | Reconnect all of the SIR components. Are all the SIR components reconnected and properly installed? | -- | Go to SIR Diagnostic System Check | --