Why Does a China VI Compliant New Vehicle Exceed Exhaust Emission Standards?
3 Answers
Reasons for excessive vehicle exhaust emissions: 1. Abnormal engine operation: The engine may experience cylinder misfiring, spark plug oil leakage, or oil channeling. When accelerating, the engine runs unevenly and lacks power. 2. Contaminated three major vehicle systems: This situation typically occurs in relatively new vehicles where test results show slight exceedances of a few percent or decimal points. It indicates that the vehicle's exhaust treatment system (including the three-way catalytic converter and oxygen sensor) isn't significantly faulty. The emission exceedance may be caused by contamination in the three major systems (intake system, exhaust system, and fuel system). 3. Three-way catalytic converter failure: This represents the primary cause of excessive vehicle exhaust emissions.
I saw a similar situation in the 4S shop workshop a couple of days ago. It sounds unbelievable for a China-6 compliant new car to have excessive exhaust emissions, but it's most likely caused by the fuel nozzle. The owner I encountered back then had refueled with 92-octane gasoline from a small gas station, which directly triggered the three-way catalytic converter alarm. Nowadays, the particulate filters in new cars are extremely sensitive; they immediately light up the warning light when encountering gasoline with excessive sulfur content. Don't rush to blame the car—first, recall where you last refueled. It's best to use Sinopec or PetroChina's 95-octane gasoline to finish this tank and then recheck. If there's still no improvement, check if the oxygen sensor plug has been loosened by a modification shop. Last time, I saw a case where the wiring harness was disturbed during a stereo upgrade. New cars meet emission standards upon leaving the factory, so such anomalies are mostly due to post-purchase usage issues.
As someone who's worked on vehicle inspection lines for over a decade, I'll tell you straight - when new cars fail emission tests, it's often not the vehicle's fault. Some cars come for retests after just 200 kilometers, with exhaust pipes hot enough to burn your hand. Testing emissions by revving a cold engine will definitely show red flags - you need to wait until coolant reaches 90°C for accurate readings. Some models have particulate filter regeneration systems - if interrupted during traffic jams, the dashboard won't show warnings but emissions go haywire. My advice? Take a highway run to let the system self-clean, and maintain 2500 RPM for three minutes before testing. I've even seen three bizarre cases where low tire pressure caused wheel speed discrepancies that messed with emission calculations.
