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Test F: Tachometer Inaccurate Or Inoperative

  1. If Instrument Panel Cluster (IPC) diagnostic system check has been performed, go to next step. If IPC diagnostic system check has not been performed, see INSTRUMENT PANEL CLUSTER DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Start engine. Observe ENGINE SPEED parameter in PCM ENGINE DATA 1 list. If ENGINE SPEED parameter matches tachometer indication, system is functioning properly at this time. Check wiring and connectors in system for intermittent fault conditions. See WIRING DIAGRAMS  . If ENGINE SPEED parameter and tachometer indication do not match, go to next step.
  3. Turn ignition switch to OFF position. Disconnect PCM connector C2. Turn ignition switch to ON position. Using DVOM, measure voltage between PCM connector C2 terminal No. 10 and ground. See Figure . See WIRING DIAGRAMS  . If measured voltage is more than 9.0 volts, go to step  6 . If measured voltage is not more than 9.0 volts, go to next step.
  4. Check White wire between PCM connector C2 terminal No. 10 and IPC connector terminal A3. See Figure . See WIRING DIAGRAMS  . Check wiring for open circuit or high resistance. Repair as necessary, then go to step  9 . If wiring is okay, go to next step.
  5. Check IPC connector for poor connections or corroded terminals. Repair connection as necessary, then go to step  9 . If no problems are found, go to step  7 .
  6. Check PCM connector for poor connections or corroded terminals. Repair connection as necessary, then go to step  9 . If no problems are found, go to step  8 .
  7. Replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION. When repair is complete, go to step  9 .
  8. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - TRUCKS article in ENGINE PERFORMANCE. When repair is complete, go to next step.
  9. Operate vehicle and ensure tachometer is operating normally. If tachometer operates normally, repair is complete. If tachometer does not operate normally, go to step  2 .
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