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Tachometer Control Circuit Diagnosis (Hombre 2.2L)

  1. Start engine. Vary engine speed. Observe tachometer. Turn ignition off. If tachometer indicated varying engine speed, go to step 11). If tachometer did not vary, go to step 2).
  2. Disconnect connector PCM. Using ohmmeter, measure resistance between PCM terminal No. 10 and ground. Resistance should be 1.2 ohms. If resistance is less than specified, go to step 3). If resistance is higher than specified, go to step 6).
  3. Disconnect instrument cluster. Using an ohmmeter, measure resistance between instrument cluster pins No. 8 and No. 11. Resistance should be 1.2 ohms. If resistance is less than specified, go to step 5). If resistance is greater than specified, go to step 4).
  4. Locate and repair short to ground on WHT (121) wire between PCM and instrument cluster. Reconnect PCM connector. Reconnect instrument cluster. Recheck tachometer operation.
  5. Replace instrument cluster. Reconnect PCM connector. Start engine and recheck tachometer operation.
  6. Disconnect instrument cluster. Connect a self-powered test light between instrument cluster connector terminal No. 8 and PCM connector terminal No. 10 for WHT (121) wire. If test light illuminates, go to step 8). If light does not illuminate, go to step 7).
  7. Locate and repair open circuit in WHT (121) wire between PCM and instrument cluster. Reconnect instrument cluster and PCM. Start engine and recheck tachometer operation.
  8. Reconnect PCM connector and instrument cluster. Using a voltmeter, backprobe terminal No. 8 WHT (121) wire of instrument cluster and ground. Start engine. Observe voltage indication. Turn ignition off. If signal voltage was present, go to step 9). If signal voltage was not present, Go to step 10).
  9. Replace instrument cluster. Start engine and recheck tachometer operation.
  10. Replace PCM. Start engine and recheck tachometer operation.
  11. Connect scan tool to DLC. Start engine. Monitor engine speed with scan tool and instrument cluster. Instrument tachometer reading should be within 100 RPM of actual engine speed. If not as specified, go to step 12).
  12. Using scan tool, monitor engine RPM. Connect a DVOM with counting capability by backprobing at in-line connector between PCM and instrument cluster WHT (121) wire and ground. Measure engine speed output from PCM on wht (121) wire. Monitor engine speed by scan tool. If PCM produces an accurate engine speed output (within 100 RPM of scan tool), go to step 14). If PCM engine speed is not within specifications, go to step 13).
  13. Replace PCM. Start engine and recheck tachometer operation.
  14. Replace instrument cluster. Start engine and recheck tachometer. Tachometer Control Circuit Diagnosis (Hombre 4.3L)
  15. Start engine. Vary engine speed. Observe tachometer. Turn ignition off. If tachometer indicated varying engine speed, go to step 11). If tachometer did not vary, go to step 2).
  16. Disconnect Ignition coil connector. Using ohmmeter, measure resistance between ignition coil terminal "B" WHT (121) wire and ground. Resistance should be 1.2 ohms. If resistance is less than specified, go to step 3). If resistance is higher than specified, go to step 6).
  17. Disconnect instrument cluster. Using an ohmmeter, measure resistance between instrument cluster pins No. 8 and No. 11. Resistance should be 1.2 ohms. If resistance is less than specified, go to step 5). If resistance is greater than specified, go to step 4).
  18. Locate and repair short to ground on WHT (121) wire between ignition coil and instrument cluster. Reconnect ignition coil connector. Reconnect instrument cluster. Start engine and recheck tachometer operation.
  19. Replace instrument cluster. Reconnect ignition coil connector. Start engine and recheck tachometer operation.
  20. Disconnect instrument cluster. Connect a self-powered test light between instrument cluster connector terminal No. 8 and ignition coil connector terminal "B" for WHT (121) wire. If test light illuminates, go to step 8). If light does not illuminate, go to step 7).
  21. Locate and repair open circuit in WHT (121) wire between ignition coil and instrument cluster. Reconnect instrument cluster and ignition coil. Start engine and recheck tachometer operation.
  22. Reconnect ignition coil connector and instrument cluster. Using a voltmeter, backprobe terminal No. 8 WHT (121) wire of instrument cluster and ground. Start engine. Observe voltage indication. Turn ignition off. If signal voltage was present, go to step 9). If signal voltage was not present, go to step 10).
  23. Replace instrument cluster. Start engine and recheck tachometer operation.
  24. Replace ignition coil. Start engine and recheck tachometer operation.
  25. Connect scan tool to DLC. Start engine. Monitor engine speed with scan tool and instrument cluster. Instrument tachometer reading should be within 100 RPM of actual engine speed. If not as specified, go to step 12).
  26. Replace instrument cluster. Start engine and recheck tachometer operation.
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