Caution: In order to avoid deploying the air bag when troubleshooting the SIR system, use only the equipment specified in this manual and the instructions given in this manual. Failure to use the specified equipment as instructed could cause air bag deployment, personal injury to you or someone else, or unnecessary SIR system repairs.

Caution: If any water enters the vehicle's interior up to the level of the carpet or higher and soaks the carpet, the sensing and diagnostic module (SDM) and the SDM harness connector may need to be replaced. The SDM could be activated when powered, which could cause deployment of the air bag(s) and result in personal injury. Before attempting these procedures, the SIR system must be disabled. Refer to Disabling the SIR System.

These diagnostic procedures will help you to find and repair SIR system malfunctions. This service category also contains information for repairing SIR system malfunctions. For best results, use the diagnostic tables, and follow the sequence listed below:

1. Perform the A Diagnostic System Check-SIR. All SIR diagnostics must begin with the A Diagnostic System Check-SIR. The A Diagnostic System Check-SIR determines the following results:

•	Proper AIR BAG warning lamp operation

•	Ability of the SDM to communicate through the data link connector (DLC)

•	Existence of SIR current and/or history diagnostic trouble codes (DTC)

2. Refer to the diagnostic table as directed by the A Diagnostic System Check-SIR. The diagnostic tables will help enable you to diagnose any SIR system malfunction. Bypassing these procedures may result in the following problems:

•	Extended diagnostic time

•	Incorrect diagnosis

•	Incorrect parts replacement

3. Repeat the A Diagnostic System Check-SIR after you perform any repairs or diagnostic procedures. This will verify that you correctly performed the repair. This will also ensure that no other malfunctions exist.

The ignition switch supplies Ignition 1 voltage through the SIR fuse to the inflatable restraint sensing and diagnostic module (SDM) at terminal A1 of the SDM connector C1 through the SDM Fuse. When the ignition switch is turned ON, the SDM responds by performing tests on the SIR system while the instrument cluster flashes the AIR BAG warning lamp seven times. Then, the SDM commands the instrument cluster to turn the AIR BAG warning lamp OFF through the Class 2 data circuit. If the SDM detects a malfunction, the SDM commands the instrument cluster to turn the AIR BAG warning lamp ON.

When an intermittent concern is indicated by a customer symptom that cannot be duplicated or by a diagnostic trouble code (DTC) that is retrieved as a history DTC without a corresponding current DTC, an intermittent condition may exist. Intermittent problems are usually caused by circuit or connector concerns. Refer to Testing for Electrical Intermittents and Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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

1. This step checks to see if the AIR BAG warning lamp flashes seven times when the ignition key is turned ON.

2. This step checks to see if the scan tool powers up.

3. This step checks to see if the scan tool can communicate with the inflatable restraint sensing and diagnostic module (SDM).

4. This step checks to see if there are any current or history diagnostic trouble codes (DTCs) present.

5. This step checks to see if there are communication DTCs (U-codes) present.

6. This step checks to see if DTC B1000 (ECU Malfunction) is present.