Quote:
Originally Posted by rick-l
There are three ways stated so far - Diagnostic tool plugged in
- drive cycle pattern
- wheel speed difference between front and back
Which one is it? All three have drawbacks.
From the quoted article... Is the EPA test chamber barometrically controlled? I'd believe the article if that were true |
1. is not the answer, otherwise a Scangauge or OBDII reader would put the car into test mode, which apparently does not happen.
Wheel speed on a dyno is reportedly one component (front wheels turning, rear wheels stationary). But if they used this method Europe it would fail, as they sell AWD diesels there.
There is a steering angle sensor built into the ZF electric power steering box, so the car knows exactly what the steering angle is, and I would guess the car is not occupied for an EPA test.
The speeds use by the EPA are very closely controlled, with 0.1 mph I believe, so a few seconds at either the low or the high speed would be another factor.
http://www3.epa.gov/nvfel/methods/la92dds.txt
And yes, I believe the atmospheric pressure is controlled.