OBD emission test question

I took my 1997 Mazda Protege in for its Illinois periodic emission
test last week. Happily, it passed, but I have a question about the
test itself.

Beginning now, Illinois is checking the OBD in all vehicles
manufactured in 1996 and later INSTEAD of the exhaust test for
hydrocarbons and CO2.

That's fine with me, but I couldn't figure out how they do it. Let me
explain.

When the car is being tested, the driver is asked to step into a kind
of waiting room from which he or she can see the car and the test
display, but can't see what the attendant is actually doing.

All I could see was the attendant perched on the end of the driver's
seat. He had in his hand an electrical device of some kind attached to
the end of a thick cable that ran up toward the ceiling and into the
booth where all the testing meters are.

The box didn't seem to be connected to anything in the car, yet
apparently some sort of data was being collected and transmitted to a
computer inside the booth.

How does this thing work? I thought there'd have to be a direct
electrical connection of some kind to a jack or other connector in the
car, but as far as I could see, there wasn't. In fact, in the
instructions on the emission test notice there's a sentence that says
that if your OBD connector is covered, it's the owner's responsibility
to remove the cover before testing. The owner's manual, however, is
virtually silent about the OBD and any cover.

Is there a transponder or transmitter of some kind in the car?

Any comment or explanation will be gratefully received.

-Len

In article >,
LenS > wrote:

> I took my 1997 Mazda Protege in for its Illinois periodic emission
> test last week. Happily, it passed, but I have a question about the
> test itself.
>
> Beginning now, Illinois is checking the OBD in all vehicles
> manufactured in 1996 and later INSTEAD of the exhaust test for
> hydrocarbons and CO2.
>
> That's fine with me, but I couldn't figure out how they do it. Let me
> explain.
>
> When the car is being tested, the driver is asked to step into a kind
> of waiting room from which he or she can see the car and the test
> display, but can't see what the attendant is actually doing.
>
> All I could see was the attendant perched on the end of the driver's
> seat. He had in his hand an electrical device of some kind attached to
> the end of a thick cable that ran up toward the ceiling and into the
> booth where all the testing meters are.
>
> The box didn't seem to be connected to anything in the car, yet
> apparently some sort of data was being collected and transmitted to a
> computer inside the booth.
>
> How does this thing work? I thought there'd have to be a direct
> electrical connection of some kind to a jack or other connector in the
> car, but as far as I could see, there wasn't. In fact, in the
> instructions on the emission test notice there's a sentence that says
> that if your OBD connector is covered, it's the owner's responsibility
> to remove the cover before testing. The owner's manual, however, is
> virtually silent about the OBD and any cover.
>
> Is there a transponder or transmitter of some kind in the car?
>
> Any comment or explanation will be gratefully received.

They plugged into the OBD2 diagnostic port, you just couldn't see
it from your vantage point.

I doubt that Envirotest would refuse to test a vehicle that had a
factory installed cover on the plug (some do, most don't), the
blurb in their literature is in regards to a non-stock cover,
something like stereo equipment or a trailer brake controller or
something intentionally mounted to circumvent them plugging in
and testing your vehicle (though some people -do- try).

The test scans your vehicles powertrain control module for
trouble codes and failed/un-run emissions monitors. There is no
transponder or transmitter. The reason your owners manual
doesn't go into great depth about the workings of the OBD2 test
port is because it is not there as a user serviceable item.

The lane attendant can not boof the test, that part has already
been anticipated and dealt with, believe me, honestly, they
really -did- plug into your vehicle.

The connector is under the dash beside the steering column...

> The test scans your vehicles powertrain control module for
> trouble codes and failed/un-run emissions monitors. There is no
> transponder or transmitter.
That's coming in OBD-III..

Regards,

Jim