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DTC P1391: Intermittent Loss Of CMP Or CKP: Testing

  1. Turn the ignition on. With the DRBIII®, 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® lab scope probe and the Miller Special Tool (6801), backprobe the CMP Signal circuit in the CMP harness connector. Start the engine. 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 Crankshaft Position Sensor and the Camshaft Position Sensor are properly installed and the mounting bolt(s) tight. Refer to any TSBs that may apply. Were any of the above conditions present? If yes, repair as necessary. If no, go to next step.
  4. Turn the ignition off. Remove the Camshaft Position 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 Camshaft Position 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® lab scope probe and the Miller Special Tool (6801), backprobe the CKP Signal circuit in the CKP harness connector. Start the engine. 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 Crankshaft Position Sensor and the Camshaft Position Sensor are properly installed and the mounting bolt(s) are tight. Refer to any TSBs that may apply. Were any of the above conditions present? If yes, repair as necessary. If no, go to next step.
  8. Turn ignition off. Remove CKP sensor. Inspect tone wheel/flexplate for damage, foreign material or excessive movement. Repair or replace tone wheel/flexplate as necessary. If tone wheel/flexplate is okay, go to next step.
  9. If no other possible causes are remaining, replace CKP sensor.
    10. 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.
  10. Turn the ignition off. With the DRBIII® lab scope probe and the Miller Special Tool (6801), backprobe the CKP Signal circuit in the PCM harness connector. Turn the ignition on, with the engine off. Observe the lab scope screen. Look for any pulses generated by the CKP Sensor. Did the CKP Sensor generate any pulses? If yes, replace the Crankshaft Position Sensor. If no, go to next step.
  11. Turn the ignition off. With the DRBIII® lab scope probe and the Miller Special Tool (6801), backprobe the CMP Signal circuit in the PCM C1 harness connector. Turn the ignition on, with the engine off. Observe the lab scope screen. Look for any pulses generated by the CMP Sensor. Did the CMP Sensor generate any pulses? If yes, replace the Camshaft Position Sensor. If no, go to next step.
  12. Turn the ignition off. With the DRBIII® lab scope probe and the Miller Special Tool (6801), backprobe the CKP Signal circuit in the PCM C1 harness connector. Start the engine. Observe the lab scope screen while wiggling the wiring harness and connectors. Were there any irregularities in the lab scope pattern? If yes, check the harness connectors carefully. If connectors are okay, replace the Crankshaft Position Sensor. If no, go to next step.
  13. Turn the ignition off. With the DRBIII® lab scope probe and the Miller Special Tool (6801), backprobe the CMP Signal circuit in the PCM harness connector. Start the engine. Observe the lab scope screen while wiggling the wiring harness and connectors. Were there any irregularities in the lab scope pattern? If yes, check the harness connectors carefully. If okay, replace the Camshaft Position Sensor. If no, go to next step.
  14. Conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® 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® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (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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