Thanks for the reply! You're absolutely right about them cracking down, and I dont want to get into the politics of that and I certainly done want to get anyone in trouble, so this is all hypothetical.
My state doesnt do visual inspections, sniff or any actual testing. They just plug into the OBD2 for monitor readiness. My cars are clean and mostly stock, usually the tech is surprised to find its a diesel........unlike my Powerstroke and Cummins trucks.

So my understanding is the tune just has to fool the stock ECU into believing the monitors' parameters are met so they pass.

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2012 BMW 2012 X5 35D
2011 BMW 2011 X5 35D
2002 BMW X5 3.0l Auto (built 10/01)
2002 BMW 325i 5 spd
1989 BMW 535i 5 spd
1989 BMW 328is Auto
1987 BMW 528e Auto
1987 BMW 328iC 5 spd