Initial Inspection and Diagnostic Overview

CIRCUIT DESCRIPTION
When the ignition switch is first turned "On" (Run), system voltage is applied from the "Air Bag" fuse to the DERM at the "IGN 1" input terminals "A3" and "B3" and from "IGN 1" fuse to the DERM at the "WLAMPHI" input. The DERM responds by flashing the "AIR BAG" telltale lamp seven times while performing tests on the SIR system.

When the engine is being cranked, system voltage is applied from the "IGN 3" fuse to the DERM at the "Crank" input. The DERM responds by grounding the "WLAMPLO" output until system voltage is removed from the "Crank" input. This results in the "Air Bag" Telltale lamp being "On" steady during cranking.

After cranking, the DERM will again flash the "Air Bag" telltale lamp seven times and perform tests on the SIR system.

NOTES ON DIAGNOSTIC SYSTEM CHECK CHART
Number(s) below refer to circled number(s) on the diagnostic system check chart.
1. The "Air Bag" telltale lamp should flash seven times after ignition is first turned "On."
2. The "Air Bag" telltale lamp should remain "On" steady during cranking. After cranking, the "Air Bag" telltale lamp should flash seven times then go "Off. " The "Air Bag" telltale lamp has successfully completed the "Bulb Check." If "Air Bag" telltale lamp remains "ON", use PDT to check for SIR Codes.
3. This test checks for the proper operations of the "Serial Data" circuit.
4. Improper operation of the "Air Bag" telltale lamp is indicated. This test differentiates a telltale lamp that stays "On" from a telltale lamp that does not come "On."

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