The ECM stores various specific data to correct the system even if there is no electrical power such as when the battery negative terminal or No. 9 IGP (15 A) fuse are disconnected. Stored data based on failed parts should be cleared by using the ‘‘CLEAR COMMAND'' of the HDS, if parts are replaced.

The HDS has three kinds of clear commands to meet this purpose. They are clear DTCs, ECM reset, and crank pattern clear. DTC clear command erases all stored DTC codes, freeze data, and on-board snapshot. This must be done with the HDS after reproducing the DTC during troubleshooting.

The ECM reset command erases all stored DTC codes, freeze data, on-board snapshot, and all specific data to correct the system except crank (CKP) pattern. If the crank (CKP) pattern data in the ECM was cleared, you must do the crank (CKP) pattern learn procedure. The crank (CKP) pattern clear command erases only crank (CKP) pattern data. This command is for repair of a misfire or the CKP sensor.