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DTC P1398: Misfire Adaptive Numerator At Limit: Testing

    NOTE: Check for any Technical Service Bulletins (TSB) that may apply to this symptom.
  1. Read and record the Freeze Frame Data. Use this information to help you duplicate the conditions that set the DTC. Pay particular attention to the DTC set conditions, such as VSS, MAP, ECT, and Load. Turn ignition on, engine not running. With the DRBIII® in the miscellaneous menu, choose Clear PCM (battery disconnect) to reset the PCM. With the DRBIII®, choose the Misfire Pretest screen. Road test the vehicle and relearn the adaptive numerator. The adaptive numerator is learned when the Adaptive Numerator Done Learning line on the Misfire Pretest screen changes to Yes. Did the adaptive numerator relearn? If yes, go to next step. If no, go to step  3.
    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. The conditions that set this 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. With the DRBIII® as a Dual Channel Lab Scope and the Miller Special Tool (6801), backprobe the related circuit at the O2 Sensor connector and PCM connector. Look for any difference in the two readings. 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.
  3. Turn ignition off. Visually inspect the related wire harness connectors. Look for broken, bent, pushed out, or corroded terminals. Visually inspect the related wire harness. Look for any chafed, pierced, pinched, or partially broken wires. Make sure the Camshaft Position Sensor is tight. Refer to any Technical Service Bulletins (TSB) that may apply. Were any problems found? If yes, repair as necessary. If no, go to next step.
  4. Turn the ignition off. Visually inspect the Crankshaft Position Sensor and related wire harness connectors. Look for broken, bent, pushed out, or corroded terminals. Visually inspect the related wire harness. Look for any chafed, pierced, pinched, or partially broken wires. Make sure the sensor mounting bolt(s) are tight. Were any problems found? If yes, repair as necessary. If no, go to next step.
  5. Disconnect and remove the crankshaft position sensor. Inspect the tone wheel/flexplate slots for damage, foreign material, or excessive movement. Is the tone wheel/flexplate free from defects? If yes, go to next step. If no, repair/replace tone wheel/flex plate as necessary.
    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 Sensor Signal circuit in the PCM harness connector. Start the engine and observe the lab scope screen for any erratic CKP Sensor pulses. Were any erratic Crankshaft Position signals detected? If yes, replace the Crankshaft Position Sensor. If no, go to next step.
    7. NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
  7. Using the wiring diagram as a guide, inspect the wire harness and connectors. Pay particular attention to all power and ground circuits. If there are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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