What Causes a Car to Fail the Exhaust Emission Test?
2 Answers
Main reasons for a car failing the exhaust emission test are as follows: 1. High sulfur and phosphorus content in gasoline, which can form chemical complexes on the surface of the oxygen sensor and the three-way catalytic converter. 2. Congested city roads with frequent stops, starts, and idling, leading to incomplete combustion products adhering to the surface of the three-way catalytic converter. 3. Carbon deposits and particulate matter in the engine can clog the three-way catalytic converter. Solutions for failing the exhaust emission test: 1. Drive in 4th gear at speeds typical for 5th gear for several dozen kilometers. 2. Keep the engine warm by not turning it off while idling, and rev the engine in neutral for 3-5 minutes before the test. 3. Regularly clean the three-way catalytic converter.
When I drive for long periods, I often encounter issues with failing emission tests, primarily due to problems with the engine's combustion system. For example, poor fuel quality can lead to incomplete combustion, producing carbon monoxide and hydrocarbons; aging spark plugs or faulty ignition coils cause misfires, resulting in increased exhaust emissions; a clogged air filter restricts airflow, leading to poor combustion due to insufficient oxygen; and a malfunctioning catalytic converter in the exhaust system, which is supposed to clean harmful gases, fails to do its job. These issues accumulate over time, and if not addressed promptly, they can worsen engine wear and even cause major failures. I've tried inspecting my car before the annual test—replacing spark plugs and the air filter improved emissions significantly. Regular maintenance, such as changing the oil and checking ignition components every 5,000 kilometers, can reduce the risk of excessive emissions and save time and fines at the inspection station.
