Ewald Böhm wrote:
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.


How do you figure that "almost no states use OBD" testing. In fact most
of the states do not use a dyno any longer.

Alaska, Arizona, California (in areas that require "enhanced" emissions
testing), Colorado, Connecticut, Georgia, Illinois, Indiana, Kentucky,
Maine, Massachusetts, Missouri (St. Louis), Nevada, New Hampshire, North
Carolina, Oregon, Texas (Houston and Dallas/Ft. Worth), Utah (Salt Lake
City), Vermont, Washington and Wisconsin, New Jersey, New York (in areas
that require emissions testing), Pennsylvania (Pittsburgh and
Philadelphia) and Virginia ALL use some type of OBD II testing, some use
both OBD II and tailpipe.

As to how it knows it's being tested. Simple, as soon as the OBD test
link gets plugged into the port it starts asking the ECM which protocol
it communicates with. Emissions testing uses a specific test protocol,
that doesn't query ALL of the systems on the vehicle. Easy enough to
tell the ECM - When this protocol is queried activate this programming.

No different than the way software is set up in some cars to change the
driving parameters based on different "modes" or valet keys or key fob type.


--
Steve W.