Test C: Speedometer/Odometer Inaccurate Or Inoperative

1. If instrument cluster diagnostic system check has been performed, go to next step. If instrument cluster diagnostic system check has not been performed, perform INSTRUMENT CLUSTER DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, near steering column. Raise and support vehicle. Start engine and place transmission into Drive. Using scan tool, observe vehicle speed parameter in Powertrain Control Module (PCM) engine data list. If vehicle speed parameter matches speedometer display, go to next step. If vehicle speed parameter does not match speedometer display, go to step  4 .
3. If odometer does not operate correctly, go to step  8 . If odometer operates correctly, inspect for intermittents. See TROUBLE SHOOTING  .
4. Turn ignition switch to OFF position. Disconnect PCM Blue 80-pin harness connector C1. PCM is located below air cleaner housing. Turn ignition switch to RUN position. Measure voltage between ground and PCM harness connector C1 terminal No. 26 (Dark Green/White wire). See Figure . If voltage is less than 9 volts, go to next step. If voltage is 9 volts or more, go to step  6 .
5. Inspect Dark Green/White wire for an open, high resistance or short to ground between PCM harness connector C1 terminal No. 26 and Instrument Panel Cluster (IPC) harness connector C2 terminal A6. See Figure and Fig 1 . If problem does not exist, go to step  7 . If problem exists, repair Dark Green/White wire as necessary. After repair, go to step  11 .
6. Inspect Dark Green/White wire for a short to voltage between PCM harness connector C1 terminal No. 26 and IPC harness connector C2 terminal A6. See Figure and Fig 1 . If problem does not exist, go to step  9 . If problem exists, repair Dark Green/White wire as necessary. After repair, go to step  11 .
7. Inspect IPC harness connector for poor connections. If problem does not exist, go to next step. If problem exists, repair IPC harness connector as necessary. After repair, go to step  11 .
8. Inspect PCM harness connector for poor connections. If problem does not exist, go to step  10 . If problem exists, repair PCM harness connector as necessary. After repair, go to step  11 .
9. Replace IPC, then go to step  11 .
10. Replace PCM. Program PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repair, go to next step.
11. Operate system to verify repair. If system is not operating correctly, repeat test beginning at step  2 .

Fig 1: Identifying Instrument Panel Cluster & Rear Integration Module Harness Connectors & Terminals

Courtesy of GENERAL MOTORS CORP.