For 1990-2009 cars

### Circuit Description

The inflatable restraint Sensing and Diagnostic Module (SDM) is equipped with a DC-DC converter to regulate the voltage to the SIR system. If the battery voltage drops, the DC-DC converter responds by increasing the voltage supply to the SIR system. If the battery voltage drops below a certain level, the SDM will respond by illuminating the AIR BAG warning lamp, but will not store a DTC. If DTCs are read when there is a low battery source voltage, the AIR BAG warning lamp will flash continously. When the source voltage returns to normal, the AIR BAG warning lamp goes out.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. This test checks to see if a discharged battery is causing the malfunction.

2. This test checks to see if there is excessive drain on the electrical system.

3. This test checks to see if the inflatable restraint Sensing and Diagnostic Module (SDM) is malfunctioning.

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. Disconnect and remove the inflatable restraint steering wheel module.
3. Disconnect the inflatable restraint IP module.
4. Disconnect both inflatable restraint front end discriminating sensors.
5. Disconnect both seat belt pretensioners.
6. Disconnect both inflatable restraint seat modules.
7. Disconnect the inflatable restraint Sensing and Diagnostic Module (SDM).
8. Turn the ignition switch to the ON position.
9. Turn the headlights and rear defogger ON.
10. Turn the windshield wipers and blower motor to HI.
11. Measure voltage from the SDM connector C2 terminal 3 to ground.

Is the voltage reading within the specified values?

6.0-11.5 V

Go to Step 3

Go to Charging System Check in Engine Electrical

3 |

1. Turn the ignition switch to the LOCK position.
2. Turn the headlights and rear defogger OFF.
3. Turn the windshield wipers and blower motor OFF.
4. Reconnect all the SIR components and make sure all the components are properly mounted.
5. Turn the ignition switch to the ON position.
6. Clear the SIR DTCs.
7. Turn the ignition switch to the ON position.
8. Turn the headlights and rear defogger ON.
9. Turn the windshield wipers and blower motor to HI.

Does the AIR BAG warning indicator go OFF after six seconds?

--

Go to Charging System Check in Engine Electrical

Go to Step 4

4 | Enter Flash Code Diagnostics. Does the AIR BAG warning indicator flash continuously? | -- | Go to Step 6 | Go to Step 5
5 |

1. Record all flashed DTCs on repair order.
2. Diagnose the DTCs from the lowest to the highest.

Have all the DTCs been diagnosed?

--

Go to Step 7

--

6 | Replace the SDM. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement . Are all the repairs complete? | -- | Go to Step 7 | --
7 | Reconnect all the SIR components. Make sure all the components are properly mounted. Have all the SIR components been reconnected and properly mounted? | -- | Go to SIR Diagnostic System Check | --