What to Do If the Vehicle Fails the Exhaust Emission Test?
4 Answers
The solutions for a vehicle failing the exhaust emission test are: 1. Perform a three-way catalytic converter cleaning maintenance on the engine, cleaning the three-way catalytic converter and oxygen sensor; 2. Replace the spark plugs, clean the distributor contacts and distributor rotor contacts, and adjust the ignition timing; 3. Clean the air filter, and replace it if it is too dirty; 4. Switch to 97-octane gasoline or 97-octane ethanol gasoline and take a high-speed drive; 5. Near the testing station, use a high-pressure pump at a car wash to add some water into the exhaust pipe, insert a filter screen into the muffler, or use a vehicle exhaust purifier by adding it to the fuel tank and idling for 20 minutes or driving 5 to 10 kilometers.
I just dealt with this issue last month, failing the emissions test can indeed be frustrating. Simply put, don’t panic—common problems are usually limited to a few culprits: A faulty catalytic converter is the most frequent offender; think of it as the car’s purifier—if it’s clogged or malfunctioning, emissions will definitely exceed limits. Oxygen sensor failures can also disrupt the air-fuel ratio, causing black smoke to puff from the exhaust. Checking the spark plugs is a must, as worn-out ones lead to incomplete combustion, which emissions tests easily flag. Also, inspect the air filter—if it’s dirty, the engine struggles to breathe, like trying to jog while wearing a mask. I recommend starting with an engine diagnostic, focusing on these areas. Don’t hesitate to replace faulty parts, and always use genuine components—post-repair retests usually pass. If all else fails, visit a specialized emissions repair shop—their expertise is invaluable.
Oh, my old car from the year before last failed the annual inspection due to exhaust emissions, which kept me busy for over half a month. Here’s a step-by-step summary: Start with the simple and inexpensive fixes, like replacing the air filter—it only costs a few dozen bucks, and if it’s clogged, it directly affects combustion. Then check the spark plugs; if the gap is too wide or there’s severe carbon buildup, replace them immediately. If that doesn’t work, focus on the catalytic converter—use a diagnostic tool to check the data stream from the front and rear oxygen sensors. Abnormal readings are likely due to the converter. The repair cost isn’t cheap; I spent over 2,000 yuan replacing mine. Finally, remember to use high-grade gasoline from reputable gas stations, as low-quality fuel can easily clog the fuel injectors and cause poor combustion. Make sure to retest when the engine is warm, as cold engines are most prone to exceeding emissions limits.
Excessive exhaust emissions may seem like a minor issue, but it's actually significant. The key is to check the fault codes - using an OBD scanner can save you a lot of trouble. For the engine, focus on the catalytic converter efficiency and air-fuel ratio values. For the aftertreatment system, pay attention to the EGR valve and crankcase ventilation device. Gasoline vehicles also need the carbon canister purge valve checked, while diesel vehicles require DPF particulate filter inspection. Maintenance recommendation: First clean the throttle body and fuel injectors, then consider replacing the oxygen sensor. If the catalyst conversion rate is below 70%, the catalytic converter must be replaced. Maintenance tip: Use fuel system cleaner every 20,000 km, and regular highway driving can effectively reduce carbon buildup. Following these steps should bring emissions within standards.
