Depending on the model year of your vehicle, Clean Air Car Check uses different types of emissions tests. All vehicles receive a Gas Cap Pressure Check, which tests to see if a vehicle's gas cap is effectively keeping fuel vapors from escaping. Fuel evaporation is a major cause of ground level smog and a properly functioning gas cap improves gas mileage by preventing fuel waste.The Second Generation On-Board Diagnostics (OBD II) Test is the most common test procedure and is used to test model year 1996 or newer vehicles. During this simple test, data is downloaded from the vehicle's on-board computer to check for emissions equipment malfunctions. An OBD scanner is attached to a connector typically located under the vehicle's dashboard.The Inspection and Maintenance (I/M 93) Test is used to test model year 1981 through 1995 or newer vehicles. During this test, an inspector drives the vehicle on a treadmill device called a dynamometer. The test simulates driving on a road. While driving, the vehicle's tailpipe emissions are captured and analyzed to evaluate the effectiveness of the vehicle's emissions control equipment. It is important that a vehicle subject to this type of test has an exhaust system that is intact and leak free. The vehicle also needs properly functioning brakes and should not have any major fluid leaks.The Single Idle Speed (BAR 90) Test is used to test 1976 to 1980 model year vehicles. A metal probe is inserted into the vehicle's tailpipe while the vehicle idles to sample the exhaust stream. At the same time, a sensor is placed on the hood of the vehicle to measure the engine speed. The probe measures the vehicle's emissions and they are analyzed to determine whether or not the vehicle's emission control equipment is working properly. The vehicle's exhaust system must be intact and leak free.