P1398 Misfire Adaptive Numerator at Limit

SYMPTOM
P-1398 MISFIRE ADAPTIVE NUMERATOR AT LIMIT

WHEN MONITORED
Under closed throttle decel; A/C off; engine coolant temp > 75 degrees; longer than 50 seconds after engine start. The speed at which the deceleration occurs must be sufficient for the given gear range, e.g., > 36 mph in first gear or> 65 in high gear.

SET CONDITION
When one of the CKP Sensor target windows (60 degrees) has more than 2.86% variance from the reference window.

POSSIBLE CAUSES
- CKP sensor connector observable defect
- CKP sensor defective
- CKP sensor not properly installed
- Notches in crankshaft defective
- Slots in flexplate defective