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DTC P1391: Intermittent Loss Of CMP Or CKP: Testing

  1. Turn ignition on. Using scan tool, read DTCs. If GOOD TRIP is displayed and equal to zero, go to next step. If GOOD TRIP is not displayed and equal to zero, go to step  13 .
  2. Using lab scope, backprobe CMP sensor signal circuit (Tan/Yellow wire) at CMP sensor connector. See Figure . Start engine and observe lab scope pattern. If CMP sensor signal pattern is not consistent, go to next step. If CMP sensor signal pattern is consistent, go to step  6 .
  3. Turn ignition off. Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires. Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals. Ensure CKP and CMP sensors are properly installed and mounting bolts are tight. Refer to any Technical service Bulletins (TSBs) that may apply. If any of these conditions are present, repair as necessary. If none of these conditions are present, go to next step.
  4. Turn ignition off. Remove CMP sensor. Inspect tone wheel/pulse ring for damage, foreign material or excessive movement. Repair or replace tone wheel/pulse ring as necessary. If tone wheel/pulse ring is okay, go to next step.
  5. If no other possible causes are remaining, replace CMP sensor.
  6. Using lab scope, backprobe CKP sensor signal circuit (Gray/Black wire) at CKP sensor connector. See Figure . Start engine and observe lab scope pattern. If CKP sensor signal pattern is not consistent, go to next step. If CKP sensor signal pattern is consistent, go to step  10 .
  7. Turn ignition off. Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires. Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals. Ensure CKP and CMP sensors are properly installed and mounting bolts are tight. Refer to any Technical service Bulletins (TSBs) that may apply. If any of these conditions are present, repair as necessary. If none of these conditions are present, 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. Turn ignition off. Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires. Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals. Ensure CKP and CMP sensors are properly installed and mounting bolts are tight. Refer to any Technical service Bulletins (TSBs) that may apply. If any of these conditions are present, repair as necessary. If none of these conditions are present, go to next step.
  11. Turn ignition off. Using lab scope, backprobe CKP signal circuit (Gray/Black wire) at terminal No. 32 at PCM C1 connector. See Figure and Figure . Start engine. Observe lab scope pattern while wiggling related wiring harness and connectors. If wiggling causes an irregular lab scope pattern, repair wiring where wiggling caused irregular lab scope pattern. If wiggling does not cause an irregular lab scope pattern, go to next step.
  12. Turn ignition off. Using lab scope, backprobe CMP signal circuit (Tan/Yellow wire) at terminal No. 33 at PCM C1 connector. Start engine. Observe lab scope pattern while wiggling related wiring harness and connectors. If wiggling causes an irregular lab scope pattern, repair wiring where wiggling caused irregular lab scope pattern. If wiggling does not cause an irregular lab scope pattern, test is complete.
  13. Turn ignition off. Using lab scope, backprobe CMP signal circuit (Tan/Yellow wire) at terminal No. 33 at PCM C1 connector. See Figure and Figure . Start engine. Observe lab scope pattern while wiggling related wiring harness and connectors. If no irregularities in lab scope pattern exist, go to next step. If any irregularities in lab scope pattern exist, carefully inspect wiring harness and connectors. Repair wiring or connectors as necessary. If wiring and connectors are okay, replace CMP sensor.
  14. Turn ignition off. Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires. Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals. Refer to any Technical service Bulletins (TSBs) that may apply. If any of these conditions are present, repair as necessary. If none of these conditions are present, go to next step.
  15. Turn ignition off. Using lab scope, backprobe CKP signal circuit (Gray/Black wire) at terminal No. 32 at PCM C1 connector. Start engine. Observe lab scope pattern while wiggling related wiring harness and connectors. If any irregularities in lab scope pattern exist, carefully inspect wiring harness and connectors. Repair wiring or connectors as necessary. If wiring and connectors are okay, replace CKP sensor. If no irregularities in lab scope pattern exist, test is complete.
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