The Scan Tool can identify the Flags or I/M Readiness Status. A flag ON for a system means that the test has been run. A flag OFF for a system means that the test has not been run. If a vehicle comes in with a problem, the technician should first look at the "Flags" screen on the Scan Tool to see if all flags were set to ON. If the EGR flag is OFF, there is a possibility that the EGR system has a fault or that the EGR system tests have not have been run (the EGR system may be okay or it may have a problem). The technician needs to drive the vehicle under the trip Conditions: and get the flag set to ON before proceeding with testing the EGR system. It should be noted that OBD II trips are different for vehicles with different body codes and engines.
If power to the PCM is removed (by removing a fuse or disconnecting the battery) the Inspection & Maintenance (I/M) Flags will be reset to "off". In effect, the vehicle must be driven under specific Conditions: until all flags are set to "on".
If the power is removed, a Scan Tool can be used to do a "quick relearn step" which resets the Fuel Trim and Idle Speed to the default settings. These steps are part of the MISC, FUNCTIONAL or SPECIAL menus found on many Aftermarket Scan Tools.