On Fri, 18 Sep 2015 22:45:53 -0400, Ed Pawlowski wrote:

I assume the car's computer
knows an instrument is plugged in so it changes the program.

Very few states use OBD emissions testing, and certainly California
doesn't yet, where California is fining VW along with the EPA.

http://www.arb.ca.gov/msprog/smogche...bd_only_im.pdf

Most use tailpipe testing.

Some, like California, run the car through the Federal Test Procedure
on a dynomometer.

Given thats at least three different procedures (where each state can
easily be different), I don't see *how* the engine computer *knows* it's
being tested for emissions.

Since almost no states use the OBD method, that's why I asked how the car
knows it is being tested.