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Test G: Tachometer Inaccurate/Inoperative

  1. If instrument panel cluster diagnostic system check has been performed, go to next step. If instrument panel cluster diagnostic system check has not been performed, go to INSTRUMENT PANEL CLUSTER DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Connect scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel. Raise vehicle drive wheels and support vehicle. Start engine. Place transmission into Drive position. Using scan tool, observe ENGINE SPEED parameter in IPC data list. If ENGINE SPEED parameter matches tachometer display, go to next step. If ENGINE SPEED parameter does not match tachometer display, leave vehicle supported and go to step  4 .
  3. If tachometer operates normally, concern maybe intermittent. See PROBLEM DIAGNOSIS  under INTERMITTENTS. If tachometer does not operate normally, go to step  12 .
  4. Turn ignition switch to OFF position. Disconnect Heating Ventilation Air Conditioning (HVAC) module 22-pin harness connector C1. HVAC harness connector C1 is located on rear of module, to access harness connector remove HVAC control module, see AUTOMATIC A/C-HEATER SYSTEMS - CATERA article. Start engine. Place transmission into Drive position. Using scan tool, observe ENGINE SPEED parameter in IPC data list. If ENGINE SPEED parameter does not match tachometer display, go to next step. If ENGINE SPEED parameter matches tachometer display, go to step  8 .
  5. Turn ignition switch to OFF position. Disconnect Engine Control Module (ECM) 64-pin harness connector C2. ECM is located left front corner of engine compartment, in ECM housing. Turn ignition switch to RUN position. Using DVOM, measure voltage between ground and ECM harness connector C2 terminal No. 35 (Green wire). See Figure . If less than 9 volts exists, go to next step. If 9 volts or more exists, go to step  7 .
  6. Check for open, high resistance or short to ground in RPM signal output circuit (Green wire) between IPC harness connectors C1 terminal No. 22 and C2 terminal No. 13, and ECM harness connector C2 terminal No. 35. See WIRING DIAGRAMS  . If problem is found, repair as necessary and go to step  14 . If no problem is found, go to step  9 .
  7. Check short to voltage in RPM signal output circuit (Green wire) between IPC harness connectors C1 terminal No. 22 and C2 terminal No. 13, and ECM harness connector C2 terminal No. 35. See WIRING DIAGRAMS  . If problem is found, repair as necessary and go to step  14 . If no problem is found, go to step  10 .
  8. Check for poor, loose or corroded terminals in HVAC harness connector. If problem is found, repair as necessary and go to step  14 . If no problem is found, go to step  11 .
  9. Check for poor, loose or corroded terminals in IPC harness connector. If problem is found, repair as necessary and go to step  14 . If no problem is found, go to step  12 .
  10. Check for poor, loose or corroded terminals in ECM harness connector. If problem is found, repair as necessary and go to step  14 . If no problem is found, go to step  13 .
  11. Replace HVAC control module. See AUTOMATIC A/C-HEATER SYSTEMS - CATERA article. After repairs are made, go to step  14 .
  12. Replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION. After repairs are made, go to step  14 .
  13. Replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION - CARS article in ENGINE PERFORMANCE. After repairs are made, go to next step.
  14. Operate system to verify repair. If system operates normally, testing is complete. If system does not operate normally, go to step  2 .
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