Today's action revises the federal vehicle inspection and maintenance (I/M) rules relating to the implementation deadline by which states are required to begin On-Board Diagnostic Checks (OBD) as a routine part of basic and enhanced I/M programs. This rule change delays to January 1, 2001, the required implementation date for OBD in basic and enhanced I/M program areas in the Ozone Transport Region (OTR) and in all other areas. During this time extension the Agency will generate, collect and analyze the data necessary to accord OBD checks the appropriate level of emission reduction credits. Additionally, certain clarifying amendments are being made to this rule to allow for updates to the Code of Federal Regulations which are cross-referenced in the OBD rule.