Passenger and light duty vehicles built for use in the United States since 1996 include an On Board Diagnostics (OBD) system. The OBD systems monitors the vehicle’s major components, including those responsible for controlling emissions. While continuously checking for issues, the OBD system identifies emissions-related problems before they might be noticed otherwise.
When the OBD system determines that a problem exists, a corresponding “diagnostic trouble code” is stored in the computer memory. If the OBD system detects a problem that may cause the vehicle emissions to exceed federal emissions standards, the Malfunction Indicator Light (MIL) or “Check Engine” light, turns on. Federal law says this dashboard light can only be used to indicate an emissions problem.
What does a FAIL test result mean?
A vehicle that has one or more Diagnostic Trouble Codes (DTC) stored in the on board computer will fail an emission test. Vehicle manufacturers determine which DTCs they consider emissions-related. Federal law only allows a Check Engine light to be turned on for an emissions-related code. Therefore, if your Check Engine light is on, your vehicle will fail the inspection.
DTCs identify an emissions component or system that needs further diagnosis to determine the best course of action for repair. Diagnostic testing and repairs should be performed by a person or facility with proper training and tools. To find an Indiana State Certified Emissions Repair Facility, you can refer to the Vehicle Emission Repair Index (VERI) brochure.
Successful repairs will result in the computer automatically clearing the trouble code which will turn off the check engine light. If the mechanic clears the trouble codes by resetting the on board computer, the vehicle will then need to be driven for three to five days doing a combination of city and highway driving before coming back for a retest. If the vehicle is retested too soon after repairs, it may receive a REJECT test result.
Part of the inspection also ensures that the Check Engine light is working properly. A vehicle will fail the inspection if the Check Engine light is not operable.