[joecool1029]

TBH, the old way of measuring emissions for diesel was to look out the back and see if there was a black cloud forming at idle and with slight throttle applied. Maybe California actually measured more, out east they didn't. It wasn't until model year 2007 that new regulation kicked in that made things a lot more strict.

For this emission issue, there was increased NOX coming out the pipe. The NOX by itself isn't a huge issue... it's when it combined with volatile organic compounds (VOC's) from trees'n shit. Then magic happens under the sun and it combines with carbon to become smog (ozone), which blows into cities and gives the kids asthma.

Some further reading: https://en.wikipedia.org/wiki/Tropospheric_ozone

EDIT: The old test handled particulate emissions... the DPF worked on these cars and no black smoke appeared until they programmed it to fail and crack (like mine!), you can't see NOX and I don't think it has a distinct smell...