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Failed Smog Test - 2001 Chevy Venture.

Just moved to CA from MI and need to register car in California. We had our 2001 Chevy Venture smog tested and it failed. The only failure was NO (PPM). At 15 mph the max is 508 and ours read 1513 and at 25 mph the max is 761 and ours read 838. We just had the oxygen sensor changed which was bad, so that shouldn't be the problem. The car has 163,000 miles on it. Any ideas?
Answer:

Since you already replaced your Chevy Venture's oxygen sensor/s I'm going to assume the "fuel feedback" system is operating properly and fuel delivery to the combustion chambers is adequate. If your Venture was not sending enough fuel to the engine you'd have a lean fuel condition and this would cause high NO. So that aside, you want to inspect the EGR (exhaust gas recirculation) system, specifically the EGR valve. The EGR valve is responsible for recirculating a small amount of exhaust gas back into the combustion chamber. This is done to cool down the chamber temperature by producing an inert gas along with the regular fuel mixture. Nitrous Oxides emissions are formed when engine chamber temperatures rise above 2500* F. Keeping the chamber cool reduces NOx emission. Your Chevy's EGR valve should be inspected to ensure its working properly. The EGR valve should be able to open and close without sticking and have its passage unrestricted to allow ample exhaust flow to the combustion chambers as needed. Other reasons your Chevy Venture may have a high NO problem are bad engine cooling, lean fuel condition (which we covered through the oxygen sensor; though the entire fuel feedback system should be diagnosed) and carbon buildup on the piston heads and interior of the combustion chambers due high mileage. These faults will cause your Chevy Venture to fail for high NO also. posted by SmogTips Support

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