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As we all know, Volkswagen is in the middle of a scandal centered on its use of special software to lower tailpipe emissions during standard emission testing protocols.

What I don't understand is why this software needed to be switched off in other circumstances. Why can't the car always operate in low-emission mode? Is there some negative effect on performance, component life?

Chris Mueller
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Gremlin
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    There is a negative effect on performance. Their most likely fix will be to switch the car to run in that mode all of the time which will reduce performance and outrage many of their customers. – Chris Mueller Sep 29 '15 at 13:28
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    It would be nice to learn what the *specific* effects on performance are, and their root causes. For example: Is the power output reduced? Is redline RPMs reduced? Does fuel economy go down? Etc... – Carlton Sep 29 '15 at 14:33
  • The adjustments that the computer has to make to the engine parameters required to meet emissions standards without resorting to using diesel exhaust fluid the way tracks now do, results in both lower fuel economy and power. – DLS3141 Sep 29 '15 at 15:07
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    @ChrisMueller They already tried a software-only fix; it wasn't good enough. They are probably going to need retrofits on many, if not all of the affected models. – Air Sep 29 '15 at 17:12
  • As I understand it, the whole issue is about the nitrogen compounds in the Diesel emissions. If you control those properly, your engine's efficiency is effected negatively and thus the carbon emissions go up. I heard some arguments that the emission standards are unreasonable and that it practically is impossible to control the N compounds and C compounds while still being economically competitive. This makes one wonder how the other car manufacturers manage ... – SlydeRule Oct 01 '15 at 05:43

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