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What to Do If Vehicle Fails Emission Test During Annual Inspection?

1 Answers
VanZoe
07/29/25 9:56pm
If a vehicle fails the emission test during annual inspection, the following three methods can be employed: 1. Clean or replace the catalytic converter: The catalytic converter's function is to oxidize CH and CO into CO2 and H2O and reduce NOx into N2, making it crucial for passing emission tests. The catalytic converter is prone to carbon buildup, clogging, poisoning, or failure. Carbon buildup and clogging are reversible and can be restored by cleaning, while poisoning, failure, or damage require replacement. 2. Clean or replace the spark plugs: Faults in the ignition system, such as spark plugs or ignition coils, can also lead to excessive vehicle emissions. Poor spark plug conditions can worsen emission pollution. Spark plugs are also susceptible to carbon buildup, which can be cleaned with sandpaper or cleaning agents to restore their function, and the ignition gap can be adjusted. However, if the spark plugs are found to be eroded or have reached the end of their service life, they should be replaced immediately. 3. Check the oxygen sensor: Oxygen sensors are divided into upstream (front) and downstream (rear) sensors. The upstream sensor monitors the post-combustion gases, and any carbon buildup or malfunction can prevent the ECU from correctly adjusting the air-fuel mixture. The downstream sensor assesses the purification efficiency of the catalytic converter, and if damaged, it cannot determine whether the catalytic converter is functioning properly. Therefore, the oxygen sensor plays a vital role in emission testing, and it is recommended to inspect and clean it along with the catalytic converter.
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