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Forum > Smog Check Repair > Question

95 Geo Metro failed for high NO. What would cause my Geo Metro to fail the smog test?

The NO at 15 mph failed ... what would cause that? Everything else looks good.
Answer:

Your Geo Metro may have failed the smog test because of a malfunctioning EGR valve. The EGR valve is responsible for re-circulating 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 NO emission. The EGR system is prone to collecting carbon build-up. Since the EGR valve pulls exhaust gasses from your exhaust and introduces them back into your engine's intake air over time it will become clogged or stuck open/closed from the carbon deposits. Have a smog check repair station inspect your Geo's EGR system. If no problem is found there, they should look into the fuel management system and make sure that your Geo Metro is not running lean. Lean fuel conditions cause high NO as well. posted by SmogTips Support

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