Test D: Scan Tool Does Not Communicate With Sensing & Diagnostic Module

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting any repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in appropriate AIR BAG RESTRAINT SYSTEMS article.

1. If data link communications system check has been performed, go to next step. If data link communications system check has not been performed, perform data link communications system check. Perform DATA LINK DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition switch to LOCK position. Remove and inspect air bag fuse (15-amp) from junction block. Junction block is located under left side of instrument panel. If air bag fuse is not blown, go to next step. If fuse is blown, go to step  8 .
3. Install air bag fuse. Disconnect Sensing and Diagnostic Module (SDM) 12-pin harness connector. SDM is located under center console. Measure resistance in Black/White wire between ground and SDM harness connector terminal No. 6. See Fig 1 . If resistance is less than 2 ohms, go to next step. If resistance is more than 2 ohms, go to step  11 .
4. Turn ignition switch to RUN position. Measure voltage between ground and SDM harness connector terminal No. 8 (Yellow/Black wire). If battery voltage exists, go to next step. If battery voltage does not exist, go to step  12 .
NOTE: Wire color changes from Purple/Red wire at SDM terminal No. 1 to Purple wire at DLC terminal No. 9 at in-line 5-pin harness connector C210. In-line harness connector C210 is located behind left side of instrument panel, near junction block.
5. Turn ignition switch to LOCK position. Measure resistance in Purple wire between DLC terminal No. 9 and SDM harness connector terminal No. 1. See Figure and Fig 1 . If resistance is less than 2 ohms, go to next step. If resistance is more than 2 ohms, go to step  13 .
6. Measure resistance between ground and SDM terminal No. 9 (Purple wire). If resistance is 2 ohms or more, go to next step. If resistance is less than 2 ohms, go to step  14 .
7. Turn ignition switch to RUN position. Measure voltage between ground and DLC terminal No. 9 (Purple wire). If more than one volt exists, go to step  15 . If less than one volt exists, go to step  16 .
8. Disconnect Sensing and Diagnostic Module (SDM) harness connector. SDM is located under center console. Check continuity between ground and SDM harness connector terminal No. 8 (Yellow/Black wire). See Fig 1 . If continuity does not exist, go to next step. If continuity exists, go to step  10 .
9. Install air bag fuse. Reconnect SDM harness connector and perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
10. Repair short to ground in Yellow/Black wire between SDM and junction block. Replace air bag fuse (15-amp) and perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
11. Repair open in Black/White wire between SDM and ground. After repairs perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
12. Repair open in Yellow/Black wire between SDM and junction block. After repairs perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
NOTE: Wire color changes from Purple/Red wire at SDM terminal No. 1 to Purple wire at DLC terminal No. 9 at in-line 5-pin harness connector C210. In-line harness connector C210 is located behind left side of instrument panel, near junction block.
13. Repair open in appropriate wire between SDM and DLC. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repairs perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
14. Repair short to ground in appropriate wire between SDM and DLC. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repairs perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
15. Repair short to voltage in appropriate wire between SDM and DLC. See DATA LINK CONNECTORS article in WIRING DIAGRAMS. After repairs, perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
16. Replace SDM. See REMOVAL & INSTALLATION in AIR BAG RESTRAINT SYSTEMS article. After repairs perform air bag system diagnostic system check. See AIR BAG SYSTEM DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.

Fig 1: Identifying Sensing & Diagnostic Module Harness Connector Terminals

Courtesy of GENERAL MOTORS CORP.