SIR Diagnostic System Check

CIRCUIT DESCRIPTION
When the ignition switch is first turned "ON" (Run), system voltage is applied from the "AIR BAG" fuse to the DERM at "Ignition 1" input terminals "A9" and "A10" and from the "GAGES" fuse to the DERM at the "Redundant Indicator Ignition 1" input terminal "B2". The DERM responds by flashing the "AIR BAG" warning lamp seven times while performing tests on the SIR system.

When the engine is being cranked, system voltage is applied from the "CRANK" fuse to the DERM at the "Crank" input terminal "B10". The DERM responds by grounding the "SIR Indicator" output terminal "B1" until system voltage is removed from the "Crank" input. This results in the "AIR BAG" warning lamp being "ON" steady during cranking.

After cranking, the DERM will flash the "AIR BAG" warning lamp six times and perform tests on the SIR system.

NOTES ON SYSTEM CHECK CHART
1. The "AIR BAG" warning lamp should flash seven times after the ignition switch is first turned "ON."
2. The "AIR BAG" warning lamp should remain "ON" steady during cranking.
3. After cranking, the "AIR BAG" warning lamp should flash six times then go "OFF."
4. This test checks for the proper operation of the "Serial Data" line. This test will also determine whether history diagnostic trouble codes are stored and, if so, identify them.
5. When the "AIR BAG" warning lamp flashes four times during "Bulb Check," this indicates a malfunction in the redundant lamp driver circuitry. These malfunctions are diagnosed by DTC 62 chart.
6. Improper operation of the "AIR BAG" warning lamp is indicated. This test differentiates a warning lamp stays "ON" condition from a warning lamp does not come "ON" condition.
7. This check differentiates a current diagnostic trouble codes exist condition from a diagnostic request enabled when not requested condition.
8. This test checks for proper operation of the "Serial Data" line. This test will also identify the stored diagnostic trouble codes and whether they are current or history.

DIAGNOSTIC AIDS
The order in which diagnostic trouble codes are diagnosed is very important. Failure to diagnose the diagnostic trouble codes in the order specified may result in extended diagnostic time, incorrect diagnosis, and incorrect parts replacement.