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.

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 SIR Diagnostic System Check. All SIR diagnostics must begin with the SIR Diagnostic System Check. The SIR Diagnostic System Check determines the following functions:

•	Proper AIR BAG warning lamp operation

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

•	Existence of SIR diagnostic trouble codes (DTC)

•	Existence of State Of Health (SOH) diagnostic trouble codes (DTC)

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

•	Extended diagnostic time

•	Incorrect diagnosis

•	Incorrect parts replacement

3. Repeat the SIR Diagnostic System Check after you perform any repair 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 the ignition 1 voltage to the inflatable restraint sensing and diagnostic module (SDM) at terminal 3 using the SIR Fuse. The ignition switch also supplies ignition 1 voltage to the instrument cluster. When the ignition switch is first turned to the RUN position, the instrument cluster responds by flashing the AIR BAG warning lamp 7 times. The SDM performs tests on the SIR system while the instrument cluster is flashing the warning lamp. If the SDM detects no malfunctions, the SDM commands the IPC to turn the warning lamp OFF. If the SDM detects a malfunction, the SDM commands the IPC in order to turn the warning lamp ON. If the instrument cluster receives no message from the SDM, the instrument cluster will turn the warning lamp ON.

Ensure that you diagnose the diagnostic trouble codes in the order specified by the SIR Diagnostic System Check. Failure to do so may result in the following conditions:

If the AIR BAG warning lamp does not flash 7 times when the ignition switch is turned to RUN, then the instrument cluster is not operating correctly.

If a State Of Health (SOH) DTC is present, refer to the diagnostic aids for that specific SOH DTC in this section.

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

1. This test checks for scan tool communication with SDM module on the Serial Data Line.

2. This test checks for scan tool communications with other modules on the Serial Data Line.

3. This test refers to the appropriate DTC Table and Diagnostic Aids for diagnosis of the current and/or history DTCs.

4. The AIR BAG warning lamp should flash seven times after the ignition switch is first turned to the RUN position.

5. The AIR BAG warning lamp indicates improper operation.