Flywheel Adaptation: Background

The ECM monitors crankshaft speed variations to help detect misfire. In order to make misfire detection very accurate, the ECM uses an adaptive program to make sure that any variations in flywheel speed are due to the actions of misfire rather than small manufacturing tolerance variations which are normally present in the flywheel trigger wheel teeth. This adaptive process occurs naturally during normal driving.

If the battery is disconnected or if the Flywheel Adaptive values are reset, the Flywheel Adaptive Status ("F ADAP") will change from READY to NOT READY. In order to be able to successfully perform an OBD II 'TRIP', the flywheel status must be changed to READY before starting the 'TRIP'.

The Flywheel Adaptive program is only active during engine fuel cut-off. The program only adapts when the throttle is closed, the engine speed is decreasing, and the ECM is in fuel cutoff. That is the only time that crankshaft speed variation is so small that it is reliable to start the adaptive process. The ECM will use one section of the flywheel signal as a reference, and "adapt" the other sections of the signal so that they match.

After a certain period of time, when the ECM is satisfied that the different sections of the flywheel signal look the same, the adaptive process stops and the Flywheel Adaptive status changes to 'READY'.