The ECM/PCM stores various specific data to correct the system even if there is no electrical power such as when the battery negative terminal is 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/PCM reset, and CKP 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/PCM reset command erases all stored DTC codes, freeze data, on-board snapshot, and all specific data to correct the system except CKP pattern. If the CKP pattern data in the ECM/PCM was cleared, you must do the CKP pattern learn procedure. The CKP pattern clear command erases only CKP pattern data. This command is for repair of a misfire or the CKP sensor.