How is the Drive Clean test done?

At an accredited Drive Clean facility, a certified inspector will drive your car or light-duty truck onto a dynamometer. This machine is like a treadmill that allows the vehicle to be "driven" on one spot. A probe is placed in the tailpipe of your vehicle. The probe is connected to a gas analyzer and computer, which can measure the concentration of nitrogen oxides, volatile organic compounds including hydrocarbons and carbon monoxide.

The vehicle is warmed up, and emissions readings are taken while the vehicle is driven on the dynamometer and then while idling. The test results are compared by a Drive Clean computer to emissions standards for the vehicle and its model year. For example, if you drive a 1986 model car, it will be tested against 1986 emissions standards, with an allowance for vehicle deterioration. If your vehicle has a safety problem, a missing catalytic converter, or releases visible smoke from the tailpipe, it will not be tested until it has been repaired. Such problems could lead to injury and/or malfunctioning of the test equipment. If your vehicle can not be tested on a dynamometer, it will be given a two-speed idle test.