Cost, Location, Frequency, and Vehicles
Davidson County requires emission inspections on 1975 and newer light duty gasoline and diesel powered vehicles. Cars and light trucks weighing 10,500 lbs. or less gross vehicle weight rate (GVWR) registered in Davidson County require an annual emission inspection. Following is a list of vehicles that are exempt from the annual emissions inspection.
- New motor vehicles being registered for the first time.
- Heavy duty motor vehicles (more than 10,500 lbs. GVWR).
- Antique motor vehicles
- Electric powered light-duty motor vehicles (excluding all hybrid vehicles); and
- Gasoline-powered light-duty motor vehicles with a designated model year prior to 1975.
The fee for the vehicle emissions inspection is $9.00.
Cash (no bills larger than $20.00) and personal checks (check# over 500) and credit cards (Visa and MasterCard) accepted.
To have your vehicle inspected, take it to one of the inspection stations listed here.
Vehicles passing inspection receive a vehicle inspection report with a tear-off certificate of compliance .
Vehicles not passing the inspection will receive a vehicle inspection report with the reason(s) the vehicle is failing.
The Nashville VIP provides a free diagnostic service to Davidson County vehicle owners whose vehicle has failed the vehicle inspection. The free service is offered by appointment at the Metro Public Health Department. You may make an appointment by calling 615-340-5656.
Vehicles that do not successfully pass the emission inspection prior to the expiration of your tags will be subject to ticketing and fines.
Vehicles which must be tested according to the requirements of the Nashville VIP and whose owners attempt to circumvent the inspection requirement by signing an affidavit that their vehicle is greater than 10,500 lbs. GVWR, or by any other means, will be subject to citation(s) and fine(s). Once the citation(s) and fine(s) have been resolved, the vehicle must still be inspected and pass the requirements of the Nashville VIP. To inquire about citation(s) and fine(s) issued by the Nashville VIP, Please call 615-340-5656.
Definition: A kit vehicle is a motor vehicle (car or truck) that is built by an individual or a manufacturer of kit cars.
In order to begin the registration process for a kit car, please contact the Nashville Vehicle Inspection Program at 615-340-5656.
1975 model year and newer light duty (not more than 10,500 lbs. GVWR) motor vehicles registered in Davidson County are subject to inspection every year. Following are the inspections vehicles are subject to.
Gasoline 1975 – 1995 (tailpipe, visual anti-tampering including catalytic converter and fuel cap check)
Gasoline 1996 and newer (OBD, data link connector check, visual anti-tampering including catalytic converter and fuel cap pressure test)
Diesel 1975 – 2001 (Curb Idle-opacity, visual anti-tampering including catalytic converter, if applicable, and fuel cap check)
Diesel 2002 and newer (OBD, data link connector check, visual anti-tampering including catalytic converter and fuel cap check)
For more information about the Davidson County inspections, please refer to the Metro Public Health Department, Vehicle Inspection Program regulations, posted at:
- Inspection and Maintenance of Light-Duty Motor Vehicles - Regulation No. 8
The tailpipe test involves inserting a probe into the vehicle’s tailpipe and measuring the hydrocarbons, carbon monoxide and carbon dioxide emissions.
Visual Anti-Tampering Test
The visual anti-tampering test involves visually observing the catalytic converter, if applicable, and a check to see that a fuel cap is properly installed.
Data Link Connector Check
The data link connector check is a visual check for the presence and condition of the data link connector used to communicate with the vehicles on-board computer.
The Fuel Cap Pressure Test
The fuel cap pressure test is performed by removing the fuel cap from the vehicle and measuring the fuel cap leakage rate while it is being pressurized.
Curb Idle – Opacity
The curb idle test is an opacity (smoke density) test performed only on 1975 – 2001 light duty diesel vehicles (not more than 10,500 lbs. GVWR) measured at engine idle speed.
The OBD (on-board diagnostics) test is performed by connecting to the vehicle’s computer via the data link connector .
Background: About OBD
The U.S. EPA (Environmental Protection Agency) indicates:
"The first generation of On-Board Diagnostic requirements, called OBD I, was developed by the California Air Resources Board (ARB) and implemented in 1988. As technology and the desire to expand On-Board Diagnostic capability increased, a second-generation of On-Board Diagnostics requirements was developed. This second version of On-Board Diagnostic capabilities is called "OBD II". The Clean Air Act Amendments of 1990 mandated that, beginning with the 1996 model year, all light-duty vehicles and trucks made available for sale outside of the state of California must also be equipped with OBDII..."
"The OBD II system monitors virtually every component that can affect the emission performance of the vehicle to ensure that the vehicle remains as clean as possible over its entire life, and assists repair technicians in diagnosing and fixing problems with the computerized engine controls. If a problem is detected, the OBD II system illuminates a warning lamp on the vehicle instrument panel to alert the driver. This warning lamp typically contains the phrase Check Engine or Service Engine Soon. The system will also store important information about the detected malfunction so that a repair technician can accurately find and fix the problem."
For more information about OBD, please refer to the U.S. EPA (Environmental Protection Agency) web site at https://www.epa.gov/obd/index.htm.
EPA Frequently Asked Questions related to OBD can be found at https://www.epa.gov/obd/questions.htm.
OBD Emissions Inspection Procedure
The OBD inspection evaluates your vehicle's emissions status via its onboard computer. The OBD inspection occurs through the connection of the inspection analyzer to the data link connector (OBD-II SAE standardized port) on the vehicle.
The vehicle is required to pass a MIL (malfunction indicator light) command on test and a bulb check test. After the vehicle has passed the MIL command on test and the bulb check test, the supported readiness monitors must be ready, and the vehicle must not have any diagnostic trouble codes (DTC) set in order to pass the OBD inspection.
Connection: To start the procedure, the inspector connects a communication cable from the emissions analyzer to the Data Link Connector located in the vehicle. The emissions analyzer simply reads data from the vehicle's computer. No changes are made to the vehicle or its data.
Communication: If the vehicle's OBD system is not communicating with the inspection analyzer, necessary repairs must be made in order for proper communication to occur between the analyzer and the vehicle’s on-board computer.
Failure: Your vehicle will fail the OBD test if the MIL is illuminated. It may also fail if the appropriate readiness monitors are set as "not ready" or if any DTC (diagnostic trouble codes) are set. Please note the following “About Readiness” section for additional important information.
About Readiness: The computer in your vehicle performs diagnostic tests on certain emissions systems while you are driving. These system monitors are usually "Ready" or "Complete", unless there's a pending problem with a particular system. Sometimes system monitors become “ not ready” if the vehicle's battery has been disconnected or if the vehicle computer's memory has been erased. As part of the OBD test, the analyzer checks to see how many of the supported system monitors are "not ready".
For 1996 – 2000 light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 2 supported readiness monitors are not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.
For 2001 and newer light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 1 supported readiness monitor is not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.
Supported readiness monitors must be set before a vehicle returns for a retest. Failing to complete the diagnostic drive cycle can cause the vehicle to fail the retest if the supported monitors are not set to ready.
Successful repairs will cause the computer to automatically clear the diagnostic trouble codes (turns off the check engine light). If a mechanic clears the trouble codes, the readiness monitors will also be cleared. Readiness monitors may be cleared when the battery is disconnected. The vehicle will then need to complete a diagnostic drive cycle in order to reset the readiness monitors before it is returned to the station for a retest.
Some self-diagnostic tests will not occur until you have driven the car at highway speeds for a certain length of time. Others will not occur until you have driven the car the required number of “drive cycles” of warming up to normal engine temperature then cooling back down.
Automobile manufacturers have various strategies for resetting the vehicle’s readiness monitors. For this reason, we cannot give you a simple list of instructions. Drive cycles are a combination of highway driving, stop and go driving, and for some vehicles, an overnight cool down period.
Specific drive cycles for your vehicle can be obtained from the vehicle’s manufacturer. Check with your mechanic to make sure that the readiness monitors have all been set to ready before bringing the vehicle back to a station to be retested.
Reminder: Unset readiness monitor(s) may cause additional test costs (each paid test receives one free retest).
Residents in Nashville/Davidson County experiencing difficulties with readiness monitors can contact the Metro Public Health Department, Vehicle Inspection Program at (615)-340-5656. Residents of counties outside of Davidson County should call the State of Tennessee Vehicle Inspection Program at 1-866-329-9632 or visit their website.
About Your OBD Vehicle's MIL: If your vehicle's MIL (malfunction indicator light) is flashing or blinking, you should have the vehicle serviced as soon as possible. The flashing light may indicate there is an engine misfire. Extensive driving with an engine misfire could damage your vehicle's catalytic converter.
Vehicles not eligible for the OBD test are inspected using one of the following tailpipe inspection procedures:
- Single-Speed Idle Inspection (1975 – 1995 Gasoline Vehicles)
- Curb Idle Opacity Inspection (1975 – 2001 Diesel Vehicles)
Single-Speed Idle Inspection
To conduct the single-speed idle inspection, a probe attached to the emission analyzer is inserted into the vehicle’s tailpipe. The vehicle’s emissions are tested at normal idle speed. If there are dual tailpipes, exhaust emissions will be measured from each tailpipe simultaneously with the exhaust emissions read as the total from both exhausts.
If the vehicle fails the first single-speed idle inspection, you will be instructed to raise the rpm of your vehicle for a short time. The vehicle will be allowed to return to normal idle speed and the emissions will be measured.
Curb Idle Opacity Inspection
To conduct the curb idle test, a calibrated opacity monitor is attached to the vehicle’s exhaust. The opacity (smoke density) of the vehicle’s exhaust emissions is measured at normal idle speed.
For Additional Questions and Comments
If you have questions, please contact us by calling the Nashville Vehicle Inspection Program toll-free hotline at 1-866-OBD-TEST (1-866-623-8378), or contact us by email at firstname.lastname@example.org. We can answer questions and assist you in finding the location of inspection stations in your area.