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Pcm Controlled Tachometer

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES article.
  2. Check instrument cluster. See INSTRUMENT PANEL article in ACCESSORIES/SAFETY EQUIPMENT in section. If instrument panel is okay, go to next step.
  3. Turn ignition switch to LOCK position. Disconnect PCM connector. Turn ignition switch to RUN position. Measure voltage between ground tachometer control circuit (White wire) at PCM harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, go to step 7).
  4. Set DVOM to 10-amp scale. Check current between ground and tachometer control circuit (White wire) at PCM harness connector. Monitor reading for about 2 minutes. DVOM should read less than .05 amps. If reading is as specified, go to step 12). If reading is not as specified, go to next step.
  5. Turn ignition switch to LOCK position. Disconnect instrument cluster harness connectors, but leave PCM connector disconnected. Measure voltage between ground and tachometer control circuit (White wire) at PCM harness connector. If zero volts exists, go to step 17). If voltage exists, go to next step.
  6. Locate and repair short to voltage in tachometer control circuit between instrument panel and PCM harness connectors. After repairs are complete, go to step 19).
  7. Check ignition feed fuse for instrument panel cluster. If fuse is blown, go to next step. If fuse is okay, go to step 9).
  8. Locate and repair short to ground in ignition feed circuit for instrument panel cluster. After repairs are complete. replace fuse and go to step 19).
  9. Disconnect instrument cluster connectors. Turn ignition switch to RUN position. Measure voltage between ground and ignition feed circuit (Pink wire) at instrument cluster harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, go to step 16).
  10. Check tachometer control circuit (White wire) for open or short to ground, between instrument cluster and PCM harness connectors. If open or short exists, repair as necessary and go to step 19). If open or short does not exist, go to next step.
  11. Check tachometer and ignition feed circuits for poor connection at instrument panel cluster and PCM. If problem exists, repair as necessary and go to step 19). If problem does not exist, go to step 17).
  12. Turn ignition switch to LOCK position. Connect PCM harness connectors. Disconnect instrument cluster connectors. Turn ignition switch to RUN position. Connect a test light between tachometer control circuit and ignition feed circuit at instrument panel harness connector. Start engine. If test light flashes, check for shorted component or circuit in the output driver circuit. Check for faulty instrument cluster. If test light does not flash, go to next step.
  13. If test light illuminates constantly, go to next step. If test light does not illuminate, go to step 15).
  14. Locate and repair the following circuit conditions:
    • Short to ground in crankshaft position sensor feed circuit.
    • Open in camshaft position sensor ground circuit.
    • Poor connection at crankshaft position sensor. After repairs are complete, go to step 19).
  15. Check for poor connection at PCM. If problem does not exist, go to step 18). If problem exists, repair as necessary and go to step 19).
  16. Locate and repair open in instrument cluster ignition feed circuit. After repairs are complete, go to step 19).
  17. Repair or replace instrument cluster as necessary. After repairs, go to step 19).
  18. Replace PCM and go to next step.
  19. Start engine. Observe tachometer. If tachometer is operating properly, system is okay at this time. If tachometer is not operating properly, repair instrument cluster as necessary.
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