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 engine controls diagnostic system check has been performed, go to next step. If engine controls diagnostic system check has not been performed, perform engine controls diagnostic system check. See ENGINE CONTROLS DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
2. Turn ignition switch to LOCK position. Connect scan tool to Data Link Connector (DLC). DLC is located under instrument panel, right of steering column. Attempt to communicate with Sensing and Diagnostic Module (SDM). If scan tool does not display SDM data, go to next step. If scan tool displays SDM data, system is okay.
3. If vehicle is equipped with Anti-Lock Brake System (ABS), go to next step. If vehicle is not equipped with ABS, go to step  5 .
4. Attempt to communicate with Brake Pressure Modulator Valve/Electronic Brake Control Module (BPMV/EBCM). If scan tool displays BPMV/EBCM data, go to next step. If scan tool does not display BPMV/EBCM data, go to step  6 .
5. Turn ignition switch to LOCK position. Disconnect SDM 20-pin harness connector. SDM is located in front of center console, under heater case. Measure resistance in White wire between DLC terminal No. 7 and SDM harness connector terminal No. 18. See Figure and Fig 1 . If resistance is 2 ohms or more, repair open in White wire between DLC and SDM. After repair, go to step  2 . If resistance is less than 2 ohms, go to step  12 .
6. Disconnect scan tool from DLC. Turn ignition switch to RUN position. Measure voltage between ground and DLC terminal No. 7 (White wire). See Figure . If battery voltage exists, go to next step. If battery voltage does not exist, go to step  8 .
7. Using a test light connected to ground, probe DLC terminal No. 7 (White wire). If test light illuminates, go to step  10 . If test light does not illuminate, go to step  11 .
8. Turn ignition switch to LOCK position. Disconnect SDM 20-pin harness connector. SDM is located in front of center console, under heater case. Measure resistance in White wire between DLC terminal No. 7 and SDM harness connector terminal No. 18. See Figure and Fig 1 . If resistance is less than 2 ohms, go to next step. If resistance is 2 ohms or more, repair open in White wire between DLC and SDM. After repair, go to step  2 .
NOTE: Serial data circuit is connected to DLC, EBCM, PCM and SDM. It may be necessary to disconnect each module to ensure module is not internally grounded. For circuit identification, see DATA LINK COMMUNICATIONS article in WIRING DIAGRAMS.
9. Repair short to ground in serial data circuit. After repair, go to step  2 .
NOTE: Serial data circuit is connected to DLC, EBCM, PCM and SDM. It may be necessary to disconnect each module to ensure module is not internally shorted to voltage. For circuit identification, see DATA LINK COMMUNICATIONS article in WIRING DIAGRAMS.
10. Repair short to voltage in serial data circuit. After repair, go to step  2 .
11. Replace defective scan tool. After repair, go to step  2 .
12. Inspect SDM harness connector for loose, corroded terminals or intermittent condition. See PROBLEM DIAGNOSIS  under INTERMITTENTS. If concern still exists, go to next step. If concern does not exist, go to step  2 .
13. Replace SDM. See appropriate AIR BAG RESTRAINT SYSTEMS article. After repair, go to step  2 .

Fig 1: Identifying Sensing & Diagnostic Module Harness Connector Terminals

Courtesy of GENERAL MOTORS CORP.