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DTC P1391: Intermittent Loss Of CMP Or CKP: Testing

  1. Turn the ignition on. With the DRBIII(R), read DTCs. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  10 .
    2. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  2. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool (6801), backprobe the CMP sensor signal circuit in the CMP harness connector. Start the engine. Allow the engine to idle. Observe the lab scope screen. Are there any irregular or missing signals? If yes, go to next step. If no, go to step  6 .
  3. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Ensure the CKP sensor and the CMP sensor are properly installed and the mounting bolt(s) tight. Refer to any Technical Service Bulletin (TSB) that may apply. Were any of the above conditions present? If yes, repair as necessary. If no, go to next step.
  4. Remove the CMP sensor. Inspect the Tone wheel/pulse ring for damage, foreign material, or excessive movement. Were any problems found? If yes, repair or replace the tone wheel/pulse ring as necessary. If no, go to next step.
  5. There are no possible causes remaining, replace CMP sensor.
    6. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  6. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool, backprobe the CKP sensor signal circuit in the CKP harness connector. Start the engine. Allow the engine to idle. Observe the lab scope screen. Are there any irregular or missing signals? If yes, go to next step. If no, go to step  10 .
  7. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Ensure the CKP sensor and the CMP sensor are properly installed and the mounting bolt(s) tight. Refer to any Technical Service Bulletin (TSB) that may apply. Were any problems found? If yes, repair as necessary. If no, go to next step.
  8. Turn the ignition off. Remove the CKP sensor. Inspect the tone wheel/flex plate slots for damage, foreign material, or excessive movement. Were any problems found? If yes, repair or replace the tone wheel/flex plate as necessary. If no, go to next step.
  9. There are no possible causes remaining, replace CKP sensor.
    10. CAUTION: DO NOT start the engine in this step.
  10. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool, backprobe the CKP sensor signal circuit in the PCM harness connector. Turn the ignition on. Observe the lab scope screen. Look for any pulses generated by the CKP sensor. Did the CKP sensor generate any pulses? If yes, replace CKP sensor. If no, go to next step.
    11. CAUTION: DO NOT start the engine in this step.
  11. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool, backprobe the CMP sensor signal circuit in the PCM harness connector. Turn the ignition on. Observe the lab scope screen. Look for any pulses generated by the CMP sensor. Did the CMP sensor generate any pulses? If yes, replace CMP sensor. If no, go to next step.
    12. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  12. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool, backprobe the CKP sensor signal circuit in the PCM harness connector. Start the engine. Allow the engine to idle. Observe the lab scope screen while wiggling related wiring harness and connectors. Were there any irregularities while wiggling related wiring harness and connectors? If yes, check the harness connectors carefully. If okay, replace CKP sensor. If no, go to next step.
    13. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  13. Turn the ignition off. With the DRBIII(R) lab scope probe and the Miller Special Tool, backprobe the CMP sensor signal circuit in the PCM harness connector. Start the engine. Allow the engine to idle. Observe the lab scope screen while wiggling related wiring harness and connectors. Were there any irregularities while wiggling related wiring harness and connectors? If yes, check the harness connectors carefully. If okay, replace CMP sensor. If no, go to next step.
    14. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  14. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With the engine running at normal operating temperature, monitor the DRBIII(R) parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
    • Review the DRBIII(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
    • Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

    Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.

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