What is a common reason vehicles fail emissions testing?

A common reason vehicles fail emissions testing is due to faulty or malfunctioning emissions control systems. Emissions control systems are designed to reduce the pollutants that vehicles emit into the atmosphere, and if any part of this system is not working correctly, it can result in excessive emissions of harmful substances. Components such as the catalytic converter, oxygen sensors, and exhaust gas recirculation systems play critical roles in ensuring a vehicle runs cleanly and efficiently. If any of these components fail or malfunction, a vehicle is likely to exceed the allowable emissions limits, leading to a failed emissions test.

While outdated technology in older car models can contribute to higher emissions, it is the specific failure of the emissions control systems that is a direct and frequent cause of test failures. Accumulation of dirt on the vehicle's exterior and incorrect tire pressure are generally not associated with emissions test failures. These factors can affect vehicle safety and performance, but they do not directly impact the emissions levels produced by the vehicle.