Test 9: Speedometer &/Or Odometer Malfunction: Diesel

1. Perform on-board diagnostic system check. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. If no DTCs exist, go to next step. If any DTCs exist, perform appropriate test. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.
2. Turn ignition off. Disconnect instrument cluster harness connector. Disconnect Brown Powertrain Control Module (PCM) harness connector C2. Disconnect vehicle speed sensor buffer harness connector. Check continuity between ground and terminal No. 14 (Dark Green wire) at instrument cluster harness connector. See Figure. If continuity exists, go to next step. If continuity does not exist, go to step  4.
NOTE: Vehicle speed circuit between instrument cluster and vehicle speed sensor buffer runs through convenience center.
3. Repair short to ground in Dark Green wire between instrument cluster and vehicle speed sensor buffer, and/or between instrument cluster and PCM. See WIRING DIAGRAMS .
4. Check continuity in Dark Green wire between terminal No. 14 at instrument cluster harness connector and terminal A6 at PCM harness connector C2. See Figure and Fig 1 . If continuity does not exist, go to next step. If continuity exists, go to step  6.
NOTE: Vehicle speed circuit between instrument cluster and vehicle speed sensor buffer runs through convenience center.
5. Repair open in Dark Green wire between instrument cluster and vehicle speed sensor buffer, and/or between instrument cluster and PCM. See WIRING DIAGRAMS .
6. Replace instrument cluster.

Fig 1: Identifying Powertrain Control Module Harness Connector Terminals

Courtesy of GENERAL MOTORS CORP.