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Q&As: On-Board Diagnostic Systems

What is OBD?

On-Board Diagnostic (OBD) is a term used to describe a computerized system that monitors the vehicle’s emission controls. This system includes self-diagnostic and reporting functions. Most 1996 and newer vehicles less than 14,000 pounds gross vehicle weight rating (GVWR) (e.g., passenger cars, pickup trucks, sport utility vehicles) are equipped with second-generation OBD systems also known as OBD II.

What are the benefits of OBD II?

OBD II systems monitor the vehicle's emission control system performance and notify the driver when defects that cause an increase in air pollution are identified. These systems have the ability to alert the driver of a problem using a malfunction indicator light, or check engine light, located on the vehicle's dashboard. OBD II also stores important information about a detected malfunction that will help a repair technician identify and correct the problem. Early diagnosis and timely repair benefit air quality, may improve fuel economy, and can prevent major repair bills.

Check Engine

Should I continue to drive my vehicle if the Check Engine light stays on or is blinking?

If the check engine light comes on, take your vehicle to a licensed repair station as soon as you can to have the problem diagnosed. A blinking or flashing light indicates a malfunction that should be addressed immediately to avoid serious damage to the engine or emission control system. Check your owner's manual for repairs that may be covered under your vehicle manufacturer's emission warranty.

Will my car receive an OBD test during a Smog Check inspection?

Most 1996 and newer model year gasoline and alternative fueled vehicles under 14,001 pounds GVWR require an OBD test during a Smog Check inspection.

Most 1998 and newer model year diesel-powered vehicles under 14,001 pounds GVWR require an OBD II test during a Smog Check inspection.

How can I help my vehicle pass the OBD II test?

Repair defects causing the malfunction indicator light to illuminate. Drive the vehicle after repair or battery replacement to run the readiness monitors (i.e., vehicle self-tests). Performing regular and proper vehicle maintenance according to your owner's manual and not tampering with the emission control equipment are keys to passing the Smog Check inspection.

What is a BAR-OIS inspection?

A BAR On-Board Diagnostic Inspection System (BAR-OIS) inspection is performed on most 2000 and newer model year gasoline, CNG, and propane vehicles, as well as 1998 and newer model year diesel vehicles. The BAR-OIS inspection omits a tailpipe test that is still applicable to older model year vehicles, but includes an OBD test and visual inspection of emission control components.

How much does the BAR-OIS test cost?

BAR does not regulate the price of inspections, so the cost of a Smog Check varies from station to station. Consumers should shop around for the best price.

What are some of the ways a vehicle can fail the new BAR-OIS test?

The following list includes possible reasons why a vehicle may not pass the BAR-OIS inspection:

  • The vehicle's malfunction indicator light, or check engine light, is illuminated or flashing. The vehicle turns this lamp on when the OBD system detects a fault found when running its self-diagnostics. Diagnostic Trouble Codes (DTCs) aiding repair typically accompany an illuminated check engine light.
  • The check engine light fails to illuminate during the bulb check. When the key is turned on and the engine is off, the bulb should turn on for a few seconds to prove that it is working.
  • A number of monitors are "not ready." This means the vehicle has not had the opportunity to complete one or more of the required self-diagnostic checks of the vehicle's OBD system. The number of allowed unready monitors varies by model year and fuel type.
  • The OBD data retrieved from the vehicle does not match what is expected for that vehicle. Plugging into an incorrect vehicle to perform the OBD inspection, or a tampered OBD system, can cause this failure. This failure may require re-inspection at a State Referee facility.
  • The vehicle fails to communicate with the OBD inspection equipment. This failure is typically caused by a vehicle design defect, wiring, or damaged OBD under dash connector.
What if my vehicle fails the BAR-OIS test?

If a vehicle fails its Smog Check, ask the inspector to provide an explanation of the reason for the failure. Schedule an appointment for a diagnosis at a station licensed to perform Smog Check repairs. This is important because Test-Only stations are licensed only to perform the Smog Check test itself. Visit BAR's station locator page to locate a licensed Smog Check Test-and-Repair station in your area.

After completion of repairs, seek re-inspection to get your vehicle’s Smog Check certificate. If there is a dispute about the results of your Smog Check inspection, call the Referee at (800) 622-7733 to make an appointment for an inspection.

How can I learn more about OBD?

Check your vehicle owner's manual or visit the Air Resources Board (ARB) website at http://www.arb.ca.gov/msprog/obdprog/obdfaq.htm for more information.