1, 2 and 3 Digit Codes: 186

Mis-fire Adaptive Numerator At Limit:

Trouble Code Number
- Scan tool BA (186)
- General scan tool P1398

Fault Message
- Mis-Fire Adaptive Numerator at Limit

Background
- Because of the need for increased engine speed resolution to detect a misfire, machining variation has to be learned. The crankshaft has two 40 degree windows that are 180 degree apart. The window for cylinders No. 1 and No. 4 is the reference window. This window position is checked against the window for cylinders No.2 and No.3. If the reference window detects a variance, the PCM will learn this variance and make the appropriate engine speed adjustment. If the variance exceeds 2.86%, the trouble code will set.

Range of Check
- Under closed throttle deceleration; NC off; engine coolant temperature above 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., above 58 km/h (36 mph) in first gear or above 105 km/h (65 mph) in high gear.

Set Condition
- When one of the CKP sensor target windows (40 degrees) has more than 2.86% variance from the reference window.

Probable Cause
- Crankshaft position sensor improperly installed.
- Crankshaft position sensor failed.
- Crankshaft position sensor crankshaft target variation. -
- Severely worn crankshaft bearings.
- Wiring harness and connectors failed.
- PCM failed.
- Low compression in one or more cylinders.