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DTC P1398: Misfire Adaptive Numerator At Limit

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: Misfire adaptive numerator is monitored during closed throttle deceleration with A/C off, engine coolant temperature more than 75°F (23.9°C) and more than 50 seconds after the engine is started. The speed that deceleration occurs must be sufficient for the given gear range. DTC may be stored in Powertrain Control Module (PCM) when one of the Crankshaft Position (CKP) sensor target windows is more than 2.86 percent variance from the reference window. Possible causes are: defective CKP sensor, improperly installed CKP sensor, defective crankshaft notches, or defective connectors or wiring.
  1. Turn ignition on with engine off. Using scan tool, read Diagnostic Trouble Codes (DTCs). If global good trip counter is displayed and equal to zero, go to next step. If global good trip counter is not displayed or displayed with a value, go to step  4.
  2. Refer to Technical Service Bulletins (TSBs) for related problems. Check FREEZE FRAME data on scan tool to determine the conditions when DTC was set. Attempt to duplicate the conditions for added diagnosis. Turn ignition on with engine off. Using scan tool, clear PCM (battery disconnect), to resent PCM. Select MIS-FIRE PRE-TEST. Road test vehicle and relearn adaptive numerator. Procedure is complete when ADAPTIVE NUMERATOR DONE LEARNING changes to YES. If adaptive numerator relearned, go to next step. If adaptive numerator did not relearn, go to step  4.
  3. Ensure ignition is off. Disconnect connector at CKP sensor. CKP sensor is located on cylinder block, behind generator, near oil filter. See Figure. Check that CKP sensor is properly installed and retaining bolt is tightened to 80 INCH lbs. (9.0 N.m). Inspect connector for corroded, pushed out, miswired or damaged terminals. If terminals are not corroded, pushed out, miswired or damaged, test is complete. If terminals are corroded, pushed out, miswired or damaged, repair connector as necessary. Perform TEST VER-5A .
  4. Ensure ignition is off. Disconnect connector at CKP sensor. CKP sensor is located on cylinder block, behind generator, near oil filter. See Figure. Inspect connector for corroded, pushed out, miswired or damaged terminals. If terminals are not corroded, pushed out, miswired or damaged, go to next step. If terminals are corroded, pushed out, miswired or damaged, repair connector as necessary. Perform TEST VER-5A .
  5. Check that CKP sensor is properly installed and retaining bolt is tightened to 80 INCH lbs. (9.0 N.m). If CKP sensor is properly installed and retaining bolt is tightened to specification, go to next step. If CKP sensor is not properly installed or retaining bolt is not tightened to specification, repair as necessary. Perform TEST VER-2A .
  6. Remove CKP sensor. Inspect notches on crankshaft for damage. Crankshaft contains 2 sets of notches ground into the No. 2 counterweight on the crankshaft. If notches on crankshaft are okay, replace CKP sensor. Perform TEST VER-2A . If notches on crankshaft are damaged, repair or replace crankshaft as necessary. Perform TEST VER-2A .
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