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Division of Motor Vehicles

Vehicle Services Inspections

On-Board Diagnostic System (OBD II)


On-board diagnostic systems (OBD) on 1996 and new vehicles will be checked as part of Delaware's vehicle inspection program. OBD technology benefits motorists, technicians, and our environment. For the motorist it monitors the vehicle's performance every time it is driven and identified problems immediately, allowing service to be done before serious problems develop. For technicians it helps accurately diagnose problems, allowing for efficient and proper repairs. For the environment it identifies problems that cause vehicle emissions to increase.


Early (pre-1996) Onboard Diagnostic System - to assist technicians in diagnosing problems in electronically controlled engine systems, manufacturers equipped them with onboard diagnostics (OBD). The first OBD system appeared on 1980 model year vehicles. These systems are often referred to as OBDI technology. Although OBDI systems were not standardized, most OBDI systems were designed to monitor fuel, ignition, and emission system components to determine if they are operating correctly. OBD is a second generation of the onboard diagnostics. This second generation is phased in starting with model year 1994 and by the 1996 model year; all light-duty vehicles sold in the United States met OBDII standards. The primary purpose of OBDII is to insure that vehicles emit the minimum amount of pollutants through their useful life.

OBDII has identified the following:

  • Standardized Data Link Connectors (DLC) and Communication Protocol - this requires the manufacturer to use a standard connector and common communication protocol.
  • Standardized Terminology - the Society of Automotive Engineers (SAE) developed standardized terminology for engine and emission control system.
  • Malfunction Indicator Light (MIL) - is a term used for the light on the instrument panel, which notifies the vehicle operator is a term used for the light on the instrument panel, which notifies the vehicle operator of an emission related problem.
  • Diagnostic Trouble Codes (DTC's) - identifies the specific area of the vehicle that is experiencing malfunction problems.
  • Freeze Frame - identified when an emission related malfunction occurs, the vehicle operating parameters that will be stored in the power train control module (PCM-OBDII).
  • System Monitors and Readiness Status - there are periodic tests run on specific systems and components to ensure that they are performing within their prescribed range.
  • Continuous Monitors - some of the vehicle components or system are continuously tested by the OBDII system. Those components consist of: (1) Misfire, (2) Fuel System and (3) Comprehensive Components.
  • Non-Continuous Monitors - These consists of: (1) EGR System, (2) O2 Sensors, (3) Catalyst, (4) Evaporative System, (5) Others if vehicle is so equipped (secondary air system, heated catalyst, and A/C system. These are items that require specific conditions before monitoring.
  • Pass/Fail Criteria For OBDII Inspection – If any of the above noted items are detected the vehicle will fail the OBDII inspection.