The number one cause of high Nox failures is the 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. Keeping the
chamber cool reduces NOx 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. It is possible
to clean the EGR valve if you remove it from your vehicle and either spray
it out or let it sit in regular gasoline.
We would recommend having this component inspected before all other
diagnosis.
posted by SmogTips Support
