For 1990-2009 cars
SIR Schematics
SIR Caution
SIR Components
Handling ESD Sensitive Parts Notice

### Circuit Description

When the ignition switch is first turned to the RUN position, the CHIME Fuse (Buick UB3) or PCM Fuse (All others) applies battery voltage to the AIR BAG warning lamp that is connected to SIR INDICATOR, terminal 7. The AIR BAG Fuse applies battery voltage to the IGNITION POSITIVE VOLTAGE input, terminal 10. The inflatable restraint Sensing and Diagnostic Module (SDM) responds by flashing the AIR BAG warning lamp seven times. If IGNITION POSITIVE VOLTAGE is outside of the normal operating voltage range (8.2 volts - 17.1 volts), the AIR BAG warning lamp will come ON solid with no DTCs set.

### Diagnostic Aids

In order to disable the shorting bar from terminal 6 to terminal 7 inside the inflatable restraint Sensing and Diagnostic Module (SDM) harness connector, the following two conditions must be met:

• | The SDM harness connector must be properly connected to the SDM.

• | The Connector Position Assurance (CPA) must be properly installed in the SDM harness connector.

When measurements are requested in this table, use the J 39200 DMM with the correct terminal adapter from the J 35616 Connector Test Adapter Kit. When an inspection for proper connection is requested, refer to Testing for Electrical Intermittents in Wiring Systems. When a wire, connector or terminal repair is requested, use the J-38125 Terminal Repair Kit and refer to Wiring Repairs in Wiring Systems.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. This test checks for sufficient IGNITION POSITIVE VOLTAGE voltage applied to the SDM.

2. This test checks for excessive IGNITION POSITIVE VOLTAGE voltage applied to the SDM.

3. This test checks for a properly installed CPA.

4. This test determines if the SDM is turning on the AIR BAG warning lamp.

5. This test checks for a damaged shorting bar.

6. This test determines whether the malfunction is a short-to-ground in CKT 358.

7. This test checks for a short between CKTs 358 and 1751.

8. An open AIR BAG Fuse would cause the AIR BAG warning lamp to come on steady.

9. This test checks whether a short-to-ground caused the AIR BAG Fuse to open.

10. This test determines whether the short-to-ground is due to a short in the wiring or internal to the SDM.

11. This test checks for a disconnected SDM.

12. This test checks for an open in the IGNITION POSITIVE VOLTAGE circuit.

#### Air Bag Warning Lamp Comes On Steady

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 OFF position.
2. Connect a scan tool to the Data Link Connector (DLC).
3. Turn the ignition switch to the RUN position.
4. Request the SIR data list display.

Is IGNITION more than the specified value?

8.2 V

Go to Step 3

Go to Step 14

3 |

1. Set the parking brake.
2. Start the engine.
3. Using the scan tool, read the SIR data list.

Is IGNITION more than the specified value?

17.1 V

Go to Charging System Check

Go to Step 4

4 |

1. Turn the ignition switch to the OFF position.
2. Inspect the inflatable restraint Sensing and Diagnostic Module (SDM) harness connector CPA.

Is the CPA properly installed?

--

Go to Step 6

Go to Step 5

5 | Properly install the CPA. Are the repairs complete? | -- | Go to SIR Diagnostic System Check | --
6 |

1. Disconnect the inflatable restraint steering wheel and I/P module yellow 2-way connectors at the base of the steering column and above the RH sound insulator.
2. Disconnect the SDM harness connector.
3. Install J 38715-96 SIR Shorting Bar Tool to the SDM harness connector.
4. Install the CPA.
5. Turn the ignition switch to the RUN position.

Does the AIR BAG warning lamp come ON steady?

--

Go to Step 7

Go to Sensing and Diagnostic Module Integrity Check

7 |

1. Turn the ignition switch to the OFF position.
2. Remove J 38715-96 from the SDM harness connector.
3. Inspect the shorting bar within the SDM harness connector.

Is the shorting bar damaged or corroded?

--

Go to Step 8

Go to Step 9

8 | Replace the SDM harness connector. Are the repairs complete? | -- | Go to Step 28 | --
9 |

1. Install J 38715-96 to the SDM harness connector.
2. Install the CPA.
3. Disconnect the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges, and Console.
4. Measure the resistance from the SDM harness connector terminal 7 to ground.

Is the resistance reading less than the specified value?

OL

Go to Step 10

Go to Step 13

10 |

1. Disconnect CKT 1751 from G301. Refer to SIR COMPONENTS.
2. Measure the resistance from the SDM harness connector terminal 7 to terminal 6.

Is the resistance reading less than the specified value?

OL

Go to Step 12

Go to Step 11

11 | Repair a short-to-ground condition in CKT 358. Are the repairs complete? | -- | Go to Step 28 | --
12 |

1. Repair the short between CKTs 358 and 1751.
2. Inspect CKT 1751 for any cut or chafed wires.

Are the repairs complete?

--

Go to Step 28

--

13 | Service the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges, and Console. Are the repairs complete? | -- | Go to Step 28 | --
14 |

1. Turn the ignition switch to the OFF position.
2. Remove the AIR BAG Fuse.
3. Inspect the AIR BAG Fuse.

Is the AIR BAG Fuse good?

--

Go to Step 20

Go to Step 15

15 |

1. Replace the AIR BAG Fuse.
2. Turn the ignition switch to the RUN position for 10 seconds.
3. Turn the ignition switch to the OFF position.
4. Remove the AIR BAG Fuse.
5. Inspect the AIR BAG Fuse.

Is the AIR BAG Fuse good?

--

Go to Step 19

Go to Step 16

16 |

1. Disconnect the SDM.
2. Replace the AIR BAG Fuse.
3. Turn the ignition switch to the RUN position for 10 seconds.
4. Turn the ignition switch to the OFF position.
5. Remove the AIR BAG Fuse.
6. Inspect the AIR BAG Fuse.

Is the AIR BAG Fuse good?

--

Go to Step 18

Go to Step 17

17 |

1. Repair a short-to-ground condition in CKT 1139.
2. Connect the SDM.
3. Replace the AIR BAG Fuse.

Are the repairs complete?

--

Go to Step 28

--

18 |

1. Replace the inflatable restraint Sensing and Diagnostic Module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement .
2. Install the AIR BAG Fuse.

Are the repairs complete?

--

Go to Step 28

--

19 | Install the AIR BAG Fuse. Are the repairs complete? | -- | Go to Step 28 | --
20 | Inspect the SDM harness connector. Is the connector secure? | -- | Go to Step 22 | Go to Step 21
21 |

1. Properly connect the SDM harness connector.
2. Install the CPA.

Are the repairs complete?

--

Go to Step 28

--

22 |

1. Disconnect the inflatable restraint steering wheel and I/P module yellow 2-way connectors located at the base of the steering column and above the RH sound insulator.
2. Disconnect the SDM.
3. Check for proper connection to the SDM at terminal 10.

Is the SDM harness connector terminal damaged or corroded?

--

Go to Step 23

Go to Step 24

23 | Replace the SDM harness connector. Refer to Wiring Repair . Are the repairs complete? | -- | Go to Step 28 | --
24 | Inspect the SDM terminals for damage or corrosion. Are any terminals damaged or corroded? | -- | Go to Step 25 | Go to Step 26
25 | Replace the inflatable restraint Sensing and Diagnostic Module (SDM). Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement . Are the repairs complete? | -- | Go to Step 28 | --
26 | Measure the resistance from the SDM harness connector terminal 10 to each terminal of the AIR BAG Fuse fuseholder. Is either resistance reading within the specified values? | 0-5 ohms | Go to Sensing and Diagnostic Module Integrity Check | Go to Step 27
27 | Repair an open condition in CKT 1139. Are the repairs complete? | -- | Go to Step 28 | --
28 | Reconnect all the SIR system 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 | --