I got a 2000 Jetta and I took it to the emissions testing place and they said I’m burning (or whatever) to much NOx and I was wondering if you can help me out with what I should do.
Is all maintenance on this car up-to-date? Is the check-engine light on?
I would think that if the Check Engine light was on, the vehicle would have failed the emission test right then and there, and there would have been no reason to insert the probe up the tail pipe.
High NOx emission is caused from elevated combustion temperatures. The EGR system is supposed introduce a small amount of exhaust gasses in to combustion process to control these temperatures.But if there were a problem with the EGR system the Check Engine would be on.
A lean fuel mixture can cause elevated combustion temperatures. But if there’s a lean condition again the Check Engine light would be on.
If the engine is running hotter than normal this elevates the combustion temperatures. An engine that’s running hotter than normal will not turn on the Check Engine light.
I’m going to agree with Tester, in that you have to check the EGR system and check for leanness. In saying that you should check them I am disagreeing with the idea that there would be codes. Maybe one could say there should be codes. But I have had both EGR system issues and fuel mix issues - that both produced noticeable driveablility problems - without ever getting any codes. Undoubtedly they would have been thrown eventually, but there is a lot of tolerance for error built into those systems. (I do not have to go through emissions testing so I couldn’t tell you a thing about actual NOX levels in my case).
So I’d say a basic round of maintenance on the EGR system and a scan of the fuel trims would be a good idea.
As for fuel trims, codes and check engine lights
The correction has to be very significant for a code to set