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DTC P1398: Misfire Adaptive Numerator At Limit: Testing

  1. Turn ignition on. Using scan tool in MISCELLANEOUS menu, select CLEAR PCM (battery disconnect) to reset PCM. Using scan tool, select MISFIRE PRETEST screen. Road test vehicle to allow relearn of adaptive numerator. Adaptive numerator is learned when ADAPTIVE NUMERATOR DONE LEARNING line on MISFIRE PRETEST screen changes to YES. If adaptive numerator relearned, go to next step. If adaptive numerator did not relearn, go to step  3 .
  2. At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, monitor parameters related to DTC while wiggling connectors and wiring harness. If value changes while wiggling connectors and wiring harness, repair connectors and wiring harness where wiggling caused value to change. If value does not change, review FREEZE FRAME data using scan tool. Attempt to duplicate condition that caused DTC to set. Check for any related technical service bulletins that may apply. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. See WIRING DIAGRAMS article. If no problems are indicated, test is complete.
  3. Turn ignition off. Disconnect CKP sensor connector. CKP sensor is mounted to left side of transmission bellhousing. CKP sensor connector is located on top of intake manifold, near firewall. Visually inspect CKP sensor wiring harness for damage. Repair wiring harness as necessary. If wiring harness is okay, visually inspect CKP sensor connector for corroded, damaged, pushed-out or miswired terminals. Repair connector as necessary. If connector is okay, ensure CKP sensor is installed properly and mounting bolts/nuts are tight. Tighten mounting bolts/nuts as necessary. See TORQUE SPECIFICATIONS in REMOVAL, OVERHAUL & INSTALLATION article. If mounting bolts/nuts are tight, go to next step.
  4. Ensure ignition is off. Remove CKP sensor. Inspect notches on flywheel/drive plate for damage or debris. Flywheel/drive plate contains 3 sets of notches which contain 4 slots in each set. Check slotted areas for damage or any foreign debris. If slotted areas on flywheel/drive plate are okay and no debris exists, go to next step. If slotted areas on flywheel/drive plate are damaged or debris exists, repair or replace flywheel/drive plate as necessary.
  5. At this time, CKP sensor is assumed to be defective. Replace CKP sensor.
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