On-Board Diagnostics (OBD) II

Frequently Asked Questions

 
 

 

Important: If your "check engine" light is on, your vehicle will automatically fail the test if it is a 1996 model year or newer.


 
 

 

 


What is OBD II?

 

On-board diagnostics (OBD II) is a complex computer package installed on 1996 and newer cars
and light trucks, and 1997 and newer diesel vehicles. This sophisticated system serves as an
advanced warning to alert vehicle owners and auto technicians of potentially high emissions.
OBD II is now being used by auto emissions testing facilities.

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What does my Diagnostic Trouble Code (DTC) mean?

Each DTC indicates the type of fault and the area of the OBD and power train/emission control system where the fault is located.. When a problem occurs which may cause the vehicles emissions to exceed applicable standards, the OBD system identifies the failure with a specific DTC, illuminates the malfunction indication light (MIL) and records a record of what has occurred. The link provided below contains a reference list of codes associated with OBD, specifically related to emission system repairs.

Link: OBD DTC Reference List for emission repairs

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Why is Ohio changing the E-Check test?

Federal regulations require Ohio to implement the OBD II test for most 1996 and newer vehicles
in place of the current tailpipe emissions test. The OBD II test will improve the testing process by
detecting problems in a vehicle's emission control systems before they cause costly repairs and
allow more harmful pollutants into Ohio's air.
 

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How does OBD II work?

The computer continuously tracks and stores information about the vehicle"s performance. The on-board computer turns on the "check engine" or "service engine soon" light if it finds a problem with the vehicle's emission control system.

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What vehicles are tested using the OBD II test?

Most 1996 or newer gasoline-powered cars and trucks up to 10,000 lbs (and 1997 and newer
diesel-powered vehicles) can be tested using OBD II. If the vehicle's computer is found to be not ready after communicating with the test equipment during the initial test, a tailpipe emissions test may be conducted.

**NOTE: BMW Series 7 owners must provide accessibility to the OBD computer by removing the cover plate prior to inspection. BMW dealers can complete this task.  We regret any inconvenience this may cause.

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What are the advantages of using the OBD II test?

OBD II identifies the causes for a vehicle to fail its emissions test. By issuing specific diagnostic
codes, OBD II pinpoints the problem, allowing repair technicians to make quicker, more effective
repairs. This saves time and money. OBD II is an early warning system that alerts vehicle owners
to emissions problems at a stage where repairs are less costly and perhaps even under warranty.
OBD II inspections also are quicker than previous tests.
 

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What does OBD II have to do with clean air?

While we have made significant achievements in improving air quality in Ohio over the last 20 years,
air pollution from automobiles remains a challenge. The number of registered vehicles in Ohio has
increased 125 percent since 1970, and vehicle miles traveled have steadily increased as well.
Newer vehicles operate cleaner due to improved technology and sophisticated emission control
systems, but these systems must be in proper working order for the vehicle emissions to remain
low. When an engine is not running as designed, performance is lost, fuel is wasted and air
pollution increases. OBD II can detect problems drivers do not. By detecting emissions control
deterioration and/or failures, and alerting the driver to the need for attention, vehicles can be
properly serviced before more serious problems develop.
 

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How is OBD II technology used to test for emissions?

OBD II testing uses a hand-held tool that plugs into the vehicle's computer and determines whether
the emissions system and components are working properly. The test downloads information stored
in the vehicle's computer to identify malfunctioning emission systems or components. Information
can be downloaded only to the E-Check computer system; no information can be altered or added
to the vehicle's computer.
 

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How sophisticated is the OBD II system?

OBD II can detect malfunctioning components and systems before more serious failures occur and even before the driver of the vehicle becomes aware of a problem. The OBD II system enables a vehicle owner to make cost-effective repairs before costly damage is done to the vehicle.

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What is the difference between the OBD II and the existing treadmill tests?

The treadmill test measures the concentration of gases coming from the vehicle's exhaust pipe.
The OBD II test is an electronic test that uses a hand-held reader device plugged into the vehicle's
computer through a port mounted under the dash. The vehicle's computer will communicate if there
are any components that are deteriorating or failing that may cause the vehicle to exceed allowable
emissions limits.
 

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Does this mean vehicles won't be tested on the dynamometer anymore?

No. Vehicles that are not equipped with the OBD II system or have an OBD II system that is not
"ready" during the initial test will continue to be tested using the dynamometer unless the vehicle is a 2005 model year or newer.  Vehicles that are 2005 model year and newer are not permitted to downgrade to the "tailpipe" test.

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How does the OBD II system notify the driver of a problem?

When an emissions control malfunction is detected, a dashboard light illuminates with the message
"check engine" or "service engine soon." If the OBD II system detects a problem, the on-board
computer stores a diagnostic trouble code that identifies the malfunction. Using an OBD II scan
tool, a repair technician can quickly retrieve the diagnostic codes and make necessary repairs,
often before a more serious problem develops.
 

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My "check engine" light is on, but my vehicle is running fine. What should I do?

If the "check engine" light is flashing, take the vehicle to a repair facility as soon as possible to prevent
major damage to your vehicle. If the light is not flashing, and you do not notice any changes to
the engine's performance, drive the vehicle in a normal manner for one week to see if the problem
corrects itself and turns the light off. If the light remains illuminated after a week of normal driving,
take the vehicle to a dealership or repair facility to fix the problem. Read your owner's manual for
further information on your vehicle's OBD II system. Your vehicle will fail the E-Check test if the "check engine" light is on.

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What does "not ready" mean?

A service technician will turn off the dashboard "check engine" light after most repairs. This resets the vehicle's emission system components to "not ready". The status remains "not ready" until the vehicle's computer has had adequate time to review the repaired component. This happens after the vehicle is driven for a period of time established by the manufacturer.

 

If the vehicle's emissions system status is "not ready" when it is presented at the E-Check station during the initial test cycle, a tailpipe emissions test may be conducted.  As of January 1, 2013, 2005 and newer model year vehicles will not be permitted to downgrade to the tailpipe test. 

 

If the vehicle is transferred to another test type, the vehicle must remain on the different test track until the vehicle passes the emissions test or receives a waiver. For example, if the vehicle undergoes an OBD II test and fails, it cannot be downgraded to a tailpipe test on a re-test; the vehicle must pass the OBD II test.

For initial and subsequent tests, if a dashboard light is on when the vehicle is presented at the E-Check station, the vehicle will fail the test.
 

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How can the vehicle status be made ready?

When a vehicle is driven through its normal drive cycle, the computer reviews the emission control
system and if the vehicle was properly repaired, the system resets itself to ready. A normal drive
cycle includes operation at both cruising speeds and in stop-and-go traffic for up to a couple
weeks. This process should be followed before bringing the vehicle in to be tested.
 

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How can the dashboard light be turned off?

After fixing the problems, the service technician may turn off the dashboard light. There are also
situations under which the vehicle's OBD II system can turn off the dashboard light automatically if
the conditions that caused a problem are no longer present. If the OBD II system evaluates a
component or system three consecutive times and no longer detects the initial problem, the
dashboard light will turn off automatically. This could happen if the gas cap is not properly tightened
after refueling. The OBD II system will detect the vapor leak and turn on the dashboard light. If the
cap is properly tightened, the situation will correct itself and the light will turn off.
 

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Why would a vehicle fail an OBD II test?

  • Malfunctioning catalytic converter
  • Faulty gas cap
  • Fuel system malfunction
  • Incorrect ignition timing
  • Malfunctioning air injection system
  • Misrouted vacuum lines
  • Contaminated engine oil
  • Faulty positive crankcase ventilation (PCV) system or exhaust gas re-circulation (EGR) system

 


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Can anyone service an OBD II-related problem?

E-Check recommends that motorists utilize qualified, trained technicians equipped with the
appropriate diagnostic and repair equipment to conduct OBD II-related service. E-Check lane
inspectors can provide a list of Ohio E-Check licensed repair facilities.
 

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If my "check engine" light is not on, will I automatically pass the OBD II test?

No. A vehicle may fail the OBD II test even when the "check engine" light is not on.

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Why must I take the OBD II test if my "check engine" light is not on?

The complete test is performed to ensure that the light is working properly and that all required
OBD II monitors have tested the emissions systems and components.

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How do I know if my vehicle is covered by warranty?

Federal law requires that the emission control systems on 1995 and newer model year vehicles
be warranted for a minimum of two years or 24,000 miles. Warranty coverage for the on-board
computer and catalytic converter (only) is extended to eight years or 80,000 miles for these same
vehicles. Many automakers provide extended warranty coverage beyond that required by law.
Depending on the model year, emission system repairs may be covered by the manufacturer.
Consult your vehicle's warranty documents or your auto dealer for more information.

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Additional questions about the Ohio E-Check Program?
Call 1-800-CAR-TEST or 1-614-644-3059.