Symptom Related Diagnostic Procedures

Circuit Description
When the ignition switch is first turned to the ON position, the SIR Fuse applies battery voltage to the inflatable restraint sensing and diagnostic module (SDM) at the Ignition 1 input, terminal 3. Battery voltage is also applied to the instrument cluster (IPC). The IPC responds by flashing the AIR BAG warning lamp seven times. The SDM performs tests on the SIR system while the IPC 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 to turn the warning lamp ON. The SDM commands the IPC over the Serial Data Line Class 2.

Diagnostic Aids
If the IPC receives no message from the SDM the IPC will do the following when the ignition is turned to the ON position:
^ Flash the AIR BAG warning lamp seven times
^ Turn the warning lamp ON
^ Set DTC U1088 (Loss of Serial Data Line Class 2 State Of Health (SOH) with the SDM) or DTC U1255 (Generic Loss of Serial Data Line Class 2 (SOH)).

When measurements are requested in this table, use J 39200 Digital Multimeter with the correct terminal adapter from J 35616-A Connector Test Adapter Kit. When a check for proper connection is requested, refer to General Electrical Diagnosis Procedures in Wiring Systems. When a wire, connector or terminal repair is requested, use J 38125-B Terminal Repair Kit and refer to Wiring Repair. SIR Wiring Repair

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. This test determines if the SDM can communicate with the scan tool.
3. This test checks for sufficient Ignition 1 voltage applied to the SDM.
5. This test determines whether the Class 2 serial data line is malfunctioning.
6. This test checks for an open SIR Fuse.
7. This tests determines whether a short-to-ground caused the SIR Fuse to open.
8. This test determines whether the short to ground is due to a short in the wiring or internal to the SDM.
12. This test checks for a disconnected SDM.
18. This test checks for an open in the Ignition 1 circuit.