What is OBD II?

OBD is short for "On-Board-Diagnostic" and simply refers to those systems that are controlled or incorporated into the new automobile computers to monitor or control systems that affect the vehicle emissions. 


The Clean Air Act of 1970 established the Environmental Protection Agency (EPA) and several graduated emission standards were established over time. Vehicle manufacturers eventually turned to electronics to control the fuel and ignition systems to meet the standards. While each manufacturer had their own systems and signals early on, the EPA eventually set standards and practices for implementation by all manufacturers. 


All cars built since January 1, 1996 have what is identified as OBD-II. Usually a problem with the emissions system will alert the driver via "CHECK ENGINE" light on the instrument panel. Should this light appear, you should see your repair technician right away. Lengthy delay in seeking repairs could cause major damage to your engine or its components. 


Why Perform OBD II Inspection?

On-Board Diagnostic systems (OBD) on 1996 and newer vehicles will be checked as part of Delaware's vehicle inspection program. OBD technology benefits motorists, repair technicians and our environment. It's good for motorists because it monitors the vehicles performance every time it is driven and identifies problems immediately allowing service to be done before more serious problems develop. It's good for repair technicians because it helps to accurately diagnose problems, allowing for efficient and proper repairs. And it's good for the environment and our health because it identifies problems that cause vehicle emissions to increase. 


If any of the following conditions are met, the vehicle will fail the OBDII inspection and the vehicle must be serviced.

  1. The Malfunction Indicator Light (MIL) does not illuminate at all when the ignition key is turned to the "key on, engine not running" position. Depending on the vehicle make, the MIL will display something similar to "Service Engine Soon" or "Check Engine".
  2. The MIL status, as indicated by the scan tool, is ON. The purpose of inspecting the MIL status is to determine if the vehicle's OBDII system has commanded the MIL to turn on based on a malfunction. In most cases, the MIL should be illuminated when the engine is running and there is a malfunction.
  3. More than the allowable numbers of monitors are not ready. The purpose of the readiness status check is to determine if the vehicle's OBDII system has tested all emission control components. If the vehicle's battery has been recently disconnected, or if trouble codes have been recently cleared with a scan tool, OBD components will be set to "not ready".
  4. Data Link Connector (DLC) is missing or damaged or there is a communication failure.


My car didn't pass.  Now what should I do?

It depends on why it didn't pass, but you will probably need to take your vehicle to a repair facility for service.

  • If the Malfunction Indicator Light (MIL) is on (the light that says "check engine" or "service engine soon"), the OBD II system has found a problem that needs to be fixed.
  • If the MIL won't light, then the bulb and/or circuitry must be repaired.
  • If the required readiness monitors are not set, usually, this is caused by routine maintenance. For example, if the battery has been disconnected for any reason, the monitors of most vehicles are reset. Also, a service technician may have to reset them as part of a repair process. Essentially, the car must be driven to reset the monitors. Some manufacturers advise driving procedures while others do not. Most vehicles will become ready just through a few days of normal driving which includes a mix of highway driving and stop-and-go, city-type driving. The vehicle manufacturer or qualified service technician is the best source for this information.


More details available at DMV OBD II FAQs Page


Winner Subaru employs a Delaware Department of Motor Vehicle certified OBD-II technician.

Schedule a Service Appointment.


  • Monday 09:00am - 08:00pm
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  • Saturday 09:00am - 06:00pm
  • Sunday Closed