DTC P1398: Misfire Adaptive Numerator At Limit: Description

Misfire adaptive numerator is monitored under closed throttle deceleration, with A/C off, engine coolant temperature more than 75°F (23.9°C) and more than 50 seconds after engine start. DTC will set in Powertrain Control Module (PCM) memory when PCM senses one of Crankshaft Position (CKP) sensor target windows has more than 2.86 percent variance from CKP sensor reference window. Possible causes for DTC to set are: improperly installed CKP sensor, defective CKP sensor, defective flywheel/flexplate, defective connectors or defective wiring.