Repair Information Area
Diagnosing a vehicle for emission inspection failure can be complicated. As a Nashville motorist, you are free to select a qualified repair technician or repair the vehicle yourself. However, due to the complexity of today's vehicles, you should strongly consider having your vehicle repairs performed by a qualified technician who is experienced in diagnosing and repairing vehicle emission systems.
Vehicles not passing the inspection will receive a vehicle inspection report with the reason(s) the vehicle is failing. After appropriate repairs are made to the vehicle, you are entitled to one free retest within ninety (90) days of the initial inspection, at any of the Middle Tennessee vehicle inspection stations.
When returning for a retest, 1975 - 1995 gasoline vehicles and all diesel vehicles will be subject to the entire anti-tampering and appropriate emissions test. 1996 and newer gasoline vehicles will only be subject to the portion of the inspection which the vehicle originally failed.
If the vehicle fails the retest, a vehicle inspection report will be provided indicating the reason(s) for failure. The vehicle must have the necessary repairs made in order for the vehicle to pass the vehicle inspection.
The next retest will cost $9.00 with the following retest (if needed) free. This cycle will continue, pay for a test, receive a free test, until the vehicle passes.
The Nashville VIP provides a free diagnostic service to Davidson County vehicle owners whose vehicle has failed the vehicle inspection. Under no circumstances will we repair the vehicle. This free service is offered by appointment only by calling the Metro Public Health Department. Our telephone number is 615-340-5656.
Emission Components Functions
Exhaust Gas Recirculation (EGR) - recirculates exhaust gasses into intake manifold and is controlled by vacuum pressure.
Spark Controls (SPK) - ensures that air/fuel mixture is ignited at the best possible moment to provide optimum efficiency, power and cleaner emissions.
Positive Crankcase Ventilation (PCV) - controls the flow of crankcase fumes into the intake manifold while preventing gases and flames from traveling in the opposite direction.
Thermostatic Air Cleaner (ACL) - supplies warm air to air intake during cold engine operation. This system is only active during cold engine warm-up only.
Fuel Evaporative System (EVAP) - Allows for proper fuel system ventilation while preventing fuel vapors from reaching the atmosphere. Catches and store vapors until engine is restarted. Vapors are then removed from storage and burned.
Catalytic Converters (OC)(TWC) - Removes/Reduces NOx, CO and HC emissions as gasses pass through it.
Fill Pipe Restrictor (FR) - prohibits the introduction of leaded fuel into the fuel tank.
Air Injection Systems (AIS) - draws filtered air in through the intake port and pushes air out the exhaust port.
Oxygen Sensor (O2s) - monitors the oxygen content of exhaust gases. It produces a voltage signal which is proportional to exhaust gas oxygen compared to outside oxygen.
Low voltage signal= lean mixture
High voltage signal= rich mixture
Computerized Engine Controls (CEC) - Monitors and controls a variety of engine/vehicle functions. CEC system is primarily an emission control system designed to maintain a 14.7: 1 air/fuel ratio under most operating conditions.
Possible Causes for Emission Failure
|High CO Readings
||High HC Readings
A. Incorrect Air fuel mixture
|| A. Defective points/electronic ignition
| B. Dirty air cleaner, choke or carb./fuel injection
|| B. Open plug wire or fouled spark plug
| C. Carburetor float level improperly adjusted
|| C. Vacuum leak
| D. Inoperative air pump
|| D. Incorrect air/fuel mixture
| E. Diluted lubricating oil
|| E. Inoperative air pump
| F. Soaked fuel evaporative canister
|| F. Incorrect ignition timing